It really is all about the glass! on Cascade Tubes (Test Site)

I Love It when a Plan Comes Together!

Thu, 23 Jul 2026 00:00:00 +0000

So yesterday I posted that the top plate was complete. Today I can say that the new spud amplifier is totally complete and ready for testing.

Bloodwood Spud Progress

Wed, 22 Jul 2026 00:00:00 +0000

The wiring on the top plate for the 6EM7 “Bloodwood” Amplifier is essentially complete.

Now for the Fun Stuff

Sat, 18 Jul 2026 00:00:00 +0000

After several false starts, and a couple of minor reshufflings, The power supply side of the new amp is complete. Now it’s time to finish up the actual amp stages and get the top plate on the chassis.

But, I Don't Have That Component!

Mon, 13 Jul 2026 00:00:00 +0000

There are a thousand small decisions we make when building a project. Some matter more than others. But anyone who’s built several projects knows that sinking feeling one gets when either you don’t have, or can’t get, a specific component called for by a design.

Another Edcor Change

Wed, 08 Jul 2026 00:00:00 +0000

I was looking at the new power transformer from Edcor for the latest project today. This is the one I talked about in my posts Failings of Memory and Weirdness with Edcor Order. I noticed a change in the new transformer. However this change I consider an upgrade.

Patience Pays Off

Wed, 08 Jul 2026 00:00:00 +0000

I took my time and was very patient. And it paid off in a finish that while not exceptional, is acceptable. I am talking about the top plate for the new amplifier, of course.

Up For Grabs

Mon, 06 Jul 2026 00:00:00 +0000

I’ve been doing some straightening and rearranging in my office and I’ve decided to thin the heard a little. I have a Superior Instruments TV-11 emission type tube tester that I haven’t looked at in over a decade. Anybody interested?

A Little More Complete

Fri, 03 Jul 2026 00:00:00 +0000

I took the time to finish the chassis wiring on the spud so that I could focus on the top plate. Now comes the tough part.

Progress on the Spud

Sun, 28 Jun 2026 00:00:00 +0000

I managed to get some time to perform the bulk of the chassis work on the new amp.

Well Worth the Trouble

Thu, 18 Jun 2026 00:00:00 +0000

Just a quick note on the new project. Ten days ago I posted about how much trouble the wood gave me because of warps and twists in my plank of Bloodwood. Well, today I can say that it was well worth the effort.

"Volume" vs "Level" Controls

Wed, 17 Jun 2026 00:00:00 +0000

Would you be surprised to learn that there is a real difference between volume controls and level controls? Unfortunately today, controls which are really “level” controls routinely get tagged with the label “Volume”. But what’s the difference?

That Was A Pain in the Backside!

Mon, 08 Jun 2026 00:00:00 +0000

I know that I said I wasn’t going to do a lot of posting about my new project, but this morning’s session is worthy of a quick note.

Revising the Dual Spud

Wed, 03 Jun 2026 00:00:00 +0000

Those paying attention to my post from May 9th already know I have a new project coming. This one is nothing new or Earth shaking. Just a slight performance upgrade to the 6EM7 Vertical Amp in a more traditional chassis.

Old Man Yells at Internet

Tue, 26 May 2026 00:00:00 +0000

Or… maybe not.

The "Curly Maple" Amplifier

Thu, 14 May 2026 00:00:00 +0000

The project page for the 6V6 Curly Maple Amplifier is now up and viewable. Take a look and let me know what you think.

As always, questions and comments are welcome.

The 6V6 "Curly Maple" Amplifier

Thu, 14 May 2026 00:00:00 +0000

Beginner Plus

This amplifier started out from a slightly different line of thinking than most of my other amplifiers. This design was to be based on an entry level build difficulty, like the Marblewood Amp, but I wanted to target some slightly different characteristics than that amplifier. The first of these is long term maintainability by someone not a typical vacuum tube enthusiast. I am planning on gifting this particular amplifier and I want the recipient to feel confident maintaining it long after I’m gone. The second is that I wanted to improve on the already excellent characteristics of the Marblewood design. I was targeting the low frequency response and the channel separation/imaging response.

Weirdness with Edcor Order

Sun, 10 May 2026 00:00:00 +0000

There was one thing about my Edcor delivery today which surprised me a bit.

Failings of Memory

Sat, 09 May 2026 00:00:00 +0000

Do you ever do a bunch of work on something and then completely forget about it? And it’s only when something else happens that you then remember what you were doing? Well, that’s what happened to me today.

The Folly of Going to 11

Mon, 23 Mar 2026 00:00:00 +0000

In my last post I discussed what it means to make an amplifier go to 11. But in spite of the issues involved, many amp builders simply can’t help themselves. Even before the first connection is made they start craving more power. However, the truth of the mater is that increasing amplifier power is almost always a fool’s errand. And even the rated power outputs of most commercial amplifiers have nothing to do with listening, and everything to do with marketing.

These Go To "11"

Thu, 05 Mar 2026 00:00:00 +0000

The year was 1984. The spoof “rockumentary” titled “This Is Spinal Tap” was just released to theaters and it was then that this immortal phrase entered the modern lexicon. I’m referring, of course, to that classic line “These go to 11”.

In the intervening 40 plus years, a million and one jokes have been made about things that go to 11; including amplifiers. As amp builders we would like to know what it takes to make our amp projects go to 11. Unfortunately, the answer is more complicated than you might think.

New Tubes in the Curly Maple

Mon, 08 Sep 2025 00:00:00 +0000

The TAD 6V6GT-STR “Redbase” Premium tubes showed up and I got them installed in the 6V6 Curly Maple amplifier. I took new voltages and have been listening to the tubes with a variety of music. These tubes are very detailed and musical. They produce a stronger bass than the 6V6Gs and a very even tonality in the ultra linear topology. I would consider these a nice upgrade for any 6V6 amplifier.

Words With New Meanings

Mon, 01 Sep 2025 00:00:00 +0000

Today marks five weeks since I hurt my ankle. And this morning I managed to do my full mile plus morning walk without any issues. My dog was happy about this as well. At 18 years old the definition of “walking it off” after such an injury meant maybe a day. I guess now over 40 years later “walking it off” means five weeks. Who knew?

But I’ve also made a slight deviation with the 6V6 Curly Maple amp.

Sometimes Life Gets Complicated

Fri, 22 Aug 2025 00:00:00 +0000

So I’ve been laying low for the last couple of months and not entirely by my own volition. I finished up the Curly Maple amp on the first of June and have not yet gotten the project page posted. But rest assured, the entire write up on the new amplifier is coming soon.

Some New Tubes

Fri, 13 Jun 2025 00:00:00 +0000

I haven’t gotten the time to complete the testing on the Curly Maple yet, but I did receive a couple of tubes for which I’ve been waiting so I can try them in the new amp.

Another JJ Bites the Dust

Mon, 02 Jun 2025 00:00:00 +0000

While working in my office today I suddenly realized that the music had stopped. Looking at the Source Selector Preamp showed that the output levels were not moving. A little investigating revealed the culprit.

The 6V6 Curly Maple Amplifier is Complete

Mon, 02 Jun 2025 00:00:00 +0000

The resistors for which I’ve been waiting to finish the amp showed up in the mail yesterday. Today I got the final resistor installed and did a full check on the amplifier.

Assembly Complete... Almost

Tue, 27 May 2025 00:00:00 +0000

I took some time yesterday to finish up the 6V6 Curly Maple assembly. Everything is complete and in place except for the main dropping resistor, Rd.

Top Plate Complete

Sun, 25 May 2025 00:00:00 +0000

I had a good bit of time to work this morning and I completed the top plate wiring. The next step is to get it affixed to the chassis.

Curly Maple Power Supply Progress

Thu, 22 May 2025 00:00:00 +0000

I carved out some more time to work on the amp today. I managed to get the entire power supply section wired in.

6V6 Curly Maple Progress

Tue, 20 May 2025 00:00:00 +0000

In spite of some other things commanding my time, I’ve finally managed to get started on the wiring for the new amplifier.

A Quick Note on Content

Wed, 14 May 2025 00:00:00 +0000

Something has come up a couple of times recently and I’d like to quickly address it once and for all.

6V6 Curly Maple Mechanical Assembly

Tue, 13 May 2025 00:00:00 +0000

I took some time this morning, now that the paint is dry on the top plate, to install the mechanical aspects of the amp. The top plate is now fully populated.

6V6 Curly Maple Amp - On the Launch Pad

Tue, 06 May 2025 00:00:00 +0000

While dealing with my other spring chores, I’ve been working to get the finish applied to the amplifier’s top plate. While not perfect, I believe it is acceptable enough for me to proceed.

Musings on the New Amplifier

Sun, 27 Apr 2025 00:00:00 +0000

I keep referring to the new amplifier as the 6V6 “Curly Maple” Amplifier. But is it really?

6V6 "Curly Maple" First Assembly

Sat, 26 Apr 2025 00:00:00 +0000

The chassis has all its coats of oil finish and things started coming together today.

Getting Closer

Tue, 22 Apr 2025 00:00:00 +0000

I managed to steal a little time over Easter to do a some work in the shop. The chassis for the new 6V6 “Curly Maple” Amplifier is coming along nicely.

Slow Progress

Sat, 19 Apr 2025 00:00:00 +0000

After some delay I have managed to finish all the metal work for the Marblewood Upgrade Amplifier. Hereafter referred to as the 6V6 Curly Maple Amplifier.

More Chaos on the Work Desk

Wed, 09 Apr 2025 00:00:00 +0000

Having performed the investigations I wanted on the gain stage on which I was working, I then moved on to another part of the project. And the chaos from a couple of days ago was nothing compared to yesterday.

Old Dog... Same Old Tricks

Mon, 07 Apr 2025 00:00:00 +0000

It seems I’m nothing if not predictable. I’m just really getting going on the assembly of the Marblewood upgrade amplifier and I’m already doing design work for another project. This is in addition to the two other amplifiers which are already in the queue.

Moving Forward

Fri, 04 Apr 2025 00:00:00 +0000

I had an opportunity to spend some time on the Marblewood upgrade amplifier. The mechanicals for this project are all coming together nicely.

A Quick Question

Mon, 31 Mar 2025 00:00:00 +0000

This site supports RSS feeds, but it’s something that isn’t differentiated in my reader statistics. So, if you regularly see new content on my site via an RSS feed would you please leave a comment to that effect below. I’m curious to see how many are using this technology.

Thanks

Update on the Marblewood Upgrade Amplifier

Mon, 31 Mar 2025 00:00:00 +0000

After getting some chores out of the way this weekend, I got an opportunity to do some chassis work. The project is proceeding well.

"Popcorn" Audio

Fri, 28 Mar 2025 00:00:00 +0000

There are some projects which are not big or flashy. Simple little things which are easy to build and fill a tiny but important niche in our audio setups. I call these “popcorn” projects.

An Update, Update, Update?

Tue, 25 Mar 2025 00:00:00 +0000

We got some unseasonably nice weather here today. Clear blue skies and about 72° outside. This meant I got some time in my shop to move projects forward.

Tone Controls?

Fri, 21 Mar 2025 00:00:00 +0000

For the last couple of days I’ve been revisiting an idea for a “tone control” preamp. I had originally decided to go one way with the design, but then something happened to change my mind. My ears got involved.

An Update on the Update

Wed, 19 Mar 2025 00:00:00 +0000

I haven’t talked about the new amp in a while so I thought I’d share current progress.

Some New 6L6s

Fri, 14 Mar 2025 00:00:00 +0000

Yesterday I auditioned some new reissue Tung-Sol 6L6GC STR tubes in the 6L6 “Spalted Alder” amp. I was quite surprised at the results.

The Other Bits

Tue, 11 Mar 2025 00:00:00 +0000

I seriously despise cheap interconnects. And I don’t mean inexpensive, I mean cheap.

Cathode Bypass and Frequency Range, Part II

Wed, 19 Feb 2025 00:00:00 +0000

In my last post I threw in a comment at the end pointing out that lowering plate load resistance will play a part in how the cathode bypass capacitor behaves. Someone asked, so I thought an example of how this affects things might be in order.

Cathode Bypass and Frequency Range

Tue, 18 Feb 2025 00:00:00 +0000

There seems to be a little confusion concerning the true effects of cathode bypass on low frequency amplifier performance. The truth is, gain benefits from cathode bypass are limited. And not by capacitor size, but by the basic design of the amplifier stage.

Shifting Priorities

Fri, 07 Feb 2025 00:00:00 +0000

Remember when I said that you can’t always get what you want? Well, it turns out you can. At least in this case. Especially if you are willing to shift some priorities.

Here We Go Again

Wed, 05 Feb 2025 00:00:00 +0000

Remember back in the beginning of January when I traced the failure of the Lacewood amplifier to a failed JJ power tube? Well, here we go again.

You Can't Always Get What You Want

Wed, 29 Jan 2025 00:00:00 +0000

Lately I’ve been looking at a revised amplifier design based on the Marblewood project. The intent of the redesign effort is threefold. First, a different and more widely available rectifier tube. Second, an improved, if slightly more complicated, power supply design. And third, some potential improvement in the low frequency response. As it turns out, you can’t always get what you want. But also, two out of three ain’t bad.

Improving Testing with Modern Technology

Thu, 16 Jan 2025 00:00:00 +0000

There are lots of practices in the DIY world that are more than a little out dated. I’m obviously not talking about using vacuum tubes but rather the methods used in building and testing the circuits we build with them. Many of these test methods came about for very good reasons; perfectly applicable at the time. But as technology has advanced the reasons for many of these practices are no longer valid. And there is really no better example of this than the practice of testing audio amplifiers with square wave (or various sawtooth or triangle wave) signals.

A Cautionary Tale

Sat, 04 Jan 2025 00:00:00 +0000

After a busy Christmas season, including a brief trip out of state between Christmas and new year, I have finally managed to get the Lacewood amplifier back up and running. As part of this effort I also identified the root cause of the initial failure. And frankly I’m a little angry about it.

I Spoke Too Soon

Thu, 19 Dec 2024 00:00:00 +0000

Remember a few weeks ago in the post When it Rains, It Pours! I said that the Lacewood V2 reservoir capacitor had likely failed? Well, I was wrong.

That Didn't Go Well!

Sat, 14 Dec 2024 00:00:00 +0000

Have you ever made a mistake? Not a typical everyday little mistake like forgetting to run an errand, but a blunder of such proportions that you’re shocked by your foolishness? One that leaves you thinking you couldn’t have been that naive, that foolish? Well I did. And it left me with significant embarrassment, as well as some smoke coming out of an amplifier.

When it Rains, It Pours!

Sun, 24 Nov 2024 00:00:00 +0000

Would you believe it? Today while listening to the 6V6 Lacewood V2 I heard a funny little popping sound and a short duration whine. It only lasted a few seconds, then it was gone. But when I walked over to the amp there was a distinct smell of “magic smoke”. Once again, the game’s afoot!

Sneaky Capacitor Failure

Fri, 22 Nov 2024 00:00:00 +0000

I have witnessed a lot of electrolytic capacitor failures. Most of these failures have occurred from improper wiring polarity or a significant over voltage condition. They generally involve an explosive emptying of the capacitor shell. These failures usually leave a smoking husk of a component and a spray of foil bits, dielectric insulation, and liquid electrolyte spewed across the circuit, chassis, and sometimes, the test technician. But recently I came across a much different failure. One which seemed to be specially concocted to sneak by without notice.

Amplifier Voltages

Mon, 18 Nov 2024 00:00:00 +0000

When testing an amplifier, the first thing I generally do is to check voltages. This is what I advise others to do as well. However, the real trick is in determining if the measured voltages are acceptable or not. And herein lies the difficulty.

Talking Substitutions

Sat, 12 Oct 2024 00:00:00 +0000

This topic comes up a lot! Someone will email me with, “I want to build {insert project here} from your web site. But…”. Sometimes it’s just that part availability varies. Sometimes people want to use parts on hand which are slightly different. Sometimes people want to substitute tubes, transformers, or whole assemblies. And sometimes people want to actually change the topology! So at what point is the amp being built no longer the design on my website?

A Slight Revision to the 6L6 "Spalted Alder" Amp

Wed, 09 Oct 2024 00:00:00 +0000

Please read the post “That Didn’t Go Well!” before following the power supply change detailed in the later half of this post.

Sometimes a design which seems fine at first can later exhibit some marginal behavior. This exact issue recently reared its head with the design of the 6L6 “Spalted Alder” amplifier.

Can We Talk?

Fri, 23 Aug 2024 00:00:00 +0000

I know it’s been a while since my last post. Things have been a little hectic for my family this summer. Hopefully I’ll be able to get back to more regular posting in a few of weeks.

But that’s not what I want to talk about. I want to talk about the major changes currently taking place in the US economy and our supply chains, and some things we as hobbyists can do to help protect ourselves from problems.

Back to Work

Thu, 30 May 2024 00:00:00 +0000

I guess that some folks have been wondering what I’ve been up to the last month or so. Well, I’ve been trying to take it easy to let a shoulder injury heal. If physical therapy can be considered “taking it easy”. In the last month I’ve learned all about labrum tears. However, today something arrived in the mail and that means it’s time to get back to work.

A Small Delay to the EL84 SE-UL Optimization

Tue, 30 Apr 2024 00:00:00 +0000

As I said the other day, “It is my estimation that the EL84 would greatly benefit from a lower percentage UL tap transformer.” Whereas there is much to be learned from the current data set taken with the Edcor GXSE10-5K transformer, I have decided that a different configuration needs to be tested as well.

More Thoughts on the EL84 SE-UL Optimization

Fri, 26 Apr 2024 00:00:00 +0000

So I’ve spent the last week looking at the data from the initial effort. I’ve retaken some data, analyzed the performance and setup, poured over data sheets and characteristics curves, listened to some music at a lot of different operating points, and I’ve drawn some initial conclusions. And I must confess I’ve gotten some interesting surprises.

EL84 SE-UL Optimization First Impression

Sun, 21 Apr 2024 00:00:00 +0000

Well, all the data for the aforementioned optimization is collected and in the computer. I’ve been chewing on the data and my notes for the last couple of hours and it’s safe to say, there is a lot more here than first meets the eye.

A Quick History Lesson

Sun, 14 Apr 2024 00:00:00 +0000

For anyone who is interested in a little more of the history of feedback development, I have posted an article from the Proceedings of the IEEE from 1999. It’s a relatively quick but informative read about the topic.

A Quick Note on Feedback in Audio Amplifiers

Sat, 13 Apr 2024 00:00:00 +0000

This may seem a non-sequitur to some. After all, I don’t post designs on this website that make use of feedback. This is simply because I don’t like the way feedback affects the sound of an audio amplifier. But that doesn’t mean that I don’t understand feedback and make use of it in other applications.

Minor Work Stoppage

Sun, 07 Apr 2024 00:00:00 +0000

We’ve had a bit of a cold and rainy snap here which has prevented me from getting to the chassis work for the new 807 amp. But that doesn’t mean I’ve been totally idle.

Slowly Contracting Test Equipment

Fri, 29 Mar 2024 00:00:00 +0000

My last post concerning unused and little used test equipment got me thinking. I decided that maybe some of the equipment I’ve accumulated over the years should really be put to better use.

Slowly Expanding Test Equipment

Sun, 24 Mar 2024 00:00:00 +0000

It never ceases to amaze me how much test equipment I have seemed to have accumulated in the last 40 years or so. And some of it has been largely overshadowed by the continuing march of technology. It seems that everything now is so feature packed that lots of the old equipment is (nearly) totally obsolete.

A Quick Note on Amplifiers

Thu, 21 Mar 2024 00:00:00 +0000

I’ve been moving some amplifiers around today, listening to some that have been idle for a while and doing a little side-by-side comparison. And I’ve been reminded of a very important fact about amplifier performance.

About that Other Amp

Mon, 04 Mar 2024 00:00:00 +0000

There is truly nothing like the smell of a freshly wound transformer.

About Transformer Grounding

Sun, 03 Mar 2024 00:00:00 +0000

When looking at schematics and builds of vacuum tube amplifiers employing output transformers some people notice a curious inconsistency. On some amplifiers, the output (i.e. secondary) side of the transformer is grounded, on others, it is not. This can lead to a dilemma for amplifier builders: To ground, or not to ground? Luckily, there are some simple guidelines which will almost always yield the correct answer.

807 Triode Investigations

Tue, 20 Feb 2024 00:00:00 +0000

In my last post, I talked about the changes I’ve made to my 807 prototype jig so that I could investigate the 400v, triode strapped, plate voltage limit. Now I’ve managed to spend some time playing with the high voltage prototype power supply and my newly modified jig. As a result, I’ve learned a surprising amount about the 807 operating as a triode.

Yup. More Testing

Thu, 15 Feb 2024 00:00:00 +0000

A comment by “Dave K” a few days ago got me thinking about how I intend to run my 807 power stage and the limitations listed on the data sheet. So it shouldn’t be a shock to anyone that I’ve decided that a little more testing is required. And that required an update of my 807 test jig.

Prototype Data Lights the Way

Sun, 11 Feb 2024 00:00:00 +0000

I have the initial set of data with the power supply prototype using the Edcor XPWR011 power transformer. It is enlightening and clearly shows which amplifier I need to build next.

Gremlins in the Machine

Sat, 10 Feb 2024 00:00:00 +0000

Be sure to look carefully at the environment where you do your work. Failure to look too closely may result in you sacrificing time and effort to the gremlins in the machine. At least that’s what just happened to me.

High Voltage Prototyping

Thu, 08 Feb 2024 00:00:00 +0000

One of the risks of becoming too familiar with vacuum tube electronics is that it’s easy to become a little careless when working around high voltages. And because of this learned carelessness, sometimes we don’t take as many precautions as we should. Especially when prototyping.

There is No Shelf

Wed, 10 Jan 2024 00:00:00 +0000

In the modern western world there is this pervasive, and slightly bizarre, idea that the advance of all things (e.g. technological, medical, political, personal comfort, success, etc.) is a monotonic increasing trend from awful to awesome. And that just because something was once done or existed, then that thing is now “in the books” and there is no reason to ever revisit that thing, whatever it was. It’s a belief that once it’s been done, it’s easy to do again. But the universe is ruled by entropy. And if you stop fighting to reduce it, it just keeps growing.

However, Sometimes You Can Learn...

Sat, 30 Dec 2023 00:00:00 +0000

I was looking at some web page data this morning and I think I may have given a false impression in my post “You Never Really Know…” back in early November.

Next Optimization Update

Sat, 30 Dec 2023 00:00:00 +0000

I’ve finished modifications to my test jig to allow the testing of the 6BQ5/EL84. It’s really a shame that so few other 9-pin power pentodes use the 9CV pinout. The 6CW5/EL86 is the only other really common one.

Waffling About the Next Amp

Sun, 24 Dec 2023 00:00:00 +0000

So as I said in my post The Next Amp, I kind of settled on the triode strapped KT88 based on the power supply. Now I’m not so sure.

Is This Normal Now?

Mon, 18 Dec 2023 00:00:00 +0000

So I’ve had an experience recently that surprised me a little. And I’m wondering if this is what other people are experiencing.

More About that SNAFU

Wed, 06 Dec 2023 00:00:00 +0000

Just in case anyone was wondering, I have made a decision about my next power tube optimization.

The Next Amp

Tue, 05 Dec 2023 00:00:00 +0000

So I’ve been thinking about my next amplifier project. And I thought I had made up my mind. Then things changed… again.

Minor Optimization SNAFU

Sun, 19 Nov 2023 00:00:00 +0000

So I’ve been reviewing EL34/6CA7 data sheets preparing for an EL34 SE-UL optimization study like the two I’ve done before for the 6V6 and 6L6. However, I’ve run into a little snag.

You Never Really Know...

Thu, 09 Nov 2023 00:00:00 +0000

Whenever I make a decision to start a project for this website, I never really know how that particular project will be received. And sometimes I get surprised. This is definitely the case with the new Source Selection Preamp.

More Work Ahead

Wed, 01 Nov 2023 00:00:00 +0000

Now that the Source Selection Preamp writeup is complete, I took a little time today to prepare for another effort.

Source Selection Preamp

Thu, 26 Oct 2023 00:00:00 +0000

The project page for the Source Selection Preamp (previously known as the Source Selection Unit) is now posted.

As always, comments and questions are more than welcome.

The Source Selection Preamp

Thu, 26 Oct 2023 00:00:00 +0000

A Different Kind of Project

This project started out a little differently from most of my projects. Most of the projects I build are dedicated units; amplifiers, preamps, headphone amps, etc. But this project was designed to fix a specific problem I was having in my office setup. The issue I was having was easily swapping between the various sources in my office system. I had a simple switch for just two sources, but the number of sources was growing and I clearly needed a more robust solution.

Many Delays

Wed, 04 Oct 2023 00:00:00 +0000

I’ve been pretty busy for the last month. But things are starting to move forward again. I’m still working on the project page for the Source Selector Unit and something new as well.

It's Truly Amazing

Fri, 18 Aug 2023 00:00:00 +0000

It really is amazing how much I can accomplish when suddenly I can’t work on all the projects which have been keeping me busy for the last month. The SSU assembly is complete and I’ve done some testing.

An Opportunity

Thu, 17 Aug 2023 00:00:00 +0000

As it turns out, there is a crew working on painting the exterior of my house today. Since I can’t work on many of my outdoor projects around the house, I thought I’d take the opportunity to get a little done on the source selector unit.

Just a Quick Note

Sun, 13 Aug 2023 00:00:00 +0000

No, I haven’t fallen off the face of the Earth. And I realize that people are waiting for the completion of the Source Selector Unit. I just got unexpectedly busy.

SSU DC Checks Complete

Thu, 13 Jul 2023 00:00:00 +0000

It took a while but the DC checkout is complete and I’m finally ready to finish assembly on the Source Selector Unit.

No More Delay on the Source Selector Unit

Wed, 05 Jul 2023 00:00:00 +0000

The resistors for which I’ve been waiting showed up this afternoon. Time to get back to work on the Source Selector Unit.

Don't Do it!

Sun, 02 Jul 2023 00:00:00 +0000

We’ve all done it or at least thought about it. It’s so easy. It’s really no big deal. It feels good. No one will ever know. Well, I’m here to tell you that eventually, you’ll regret it.

The Internet is a Numbers Game

Fri, 30 Jun 2023 00:00:00 +0000

I think that most people understand that the internet is a low engagement medium. The vast majority of those browsing the internet are data consumers not contributors. But I don’t think most people really have any idea of the scale upon which this is true.

Small Delay to the Source Selector Unit

Thu, 29 Jun 2023 00:00:00 +0000

As I said before, I decided perform the DC testing of the tube assembly for the source Selector Unit in the clamping fixture. But just as I started testing, I ran into a little problem.

Completed Tube Assembly

Tue, 27 Jun 2023 00:00:00 +0000

I got some time today to finish out the vacuum tube assembly of the source selector unit.

Fixing a Mistake

Tue, 20 Jun 2023 00:00:00 +0000

So last night I posted about a mistake I made in wiring the latest project. And because of when and where I made that mistake, it took all afternoon to correct it.

I Can't Believe...

Tue, 20 Jun 2023 00:00:00 +0000

I can’t believe I did that! How could I have been so thick headed to make this kind of mistake?

Signal Sections Fully Wired

Sat, 17 Jun 2023 00:00:00 +0000

Yesterday I was bottling mead but today I got a chance to wire up the buffers and tie in the coupling capacitors. This completes installation of all the signal chain components. All that’s left on the assembly is the final power supply wiring.

Tube Wiring Progress

Wed, 14 Jun 2023 00:00:00 +0000

Between regular chores, gardening, and yard work today I managed to steal a little time to make some progress on the latest project. The gain stages for the source selector unit are essentially complete and I’ll begin working on the buffers as soon as I can.

Always Check Your Work

Mon, 12 Jun 2023 00:00:00 +0000

While I was preparing to begin assembly of the vacuum tube circuits for the Source Selector Unit, I was quickly going over the design and pulling components. And this is when I became aware of a little problem with the buffer circuit.

Source Selector Chassis Wiring Complete

Sat, 10 Jun 2023 00:00:00 +0000

I had the opportunity today to sit down and finish up the wiring on the source selector unit chassis. It has been a productive week for this project. Now that the chassis is in good shape, I’m free to move on to the assembly and wiring of the vacuum tube circuits.

Selector Pigtails and Chassis Wiring

Thu, 08 Jun 2023 00:00:00 +0000

I made some progress today on the Source Selector Unit. The twelve twisted pairs are all soldered to the selector switch and I managed some chassis wiring as well.

Source Selector Chassis in One Piece

Thu, 08 Jun 2023 00:00:00 +0000

This morning after installing the selector switch and all its pigtails in the chassis, I decided to install the base plate. The chassis in now all in a single assembly.

Wiring in Technicolor

Tue, 06 Jun 2023 00:00:00 +0000

So what does one do when needing to keep twelve signal paths clearly separated and easily identified in a chassis? Actually the answer is remarkably simple.

Source Selector Unit Chassis Taking Shape

Sat, 03 Jun 2023 00:00:00 +0000

I’ve been waiting for some wire I needed for twisted pairs and a Fender style fuse holder. I really like these fuse holders. I find them sturdy, good looking, and reliable. I have some cheaper ones but I reserve those for brassboards, quick projects, test equipment, and the like. While I’ve been waiting for my deliveries, I’ve been populating the chassis.

New Preamp is Moving Forward

Mon, 29 May 2023 00:00:00 +0000

I’ve finally completed the finishing of the bubinga chassis. It has four coats of hand rubbed oil finish. It really makes the wood grain stand out.

About that Volume Control - Part II

Sun, 28 May 2023 00:00:00 +0000

This topic is just the gift that keeps on giving. I first introduced the 4S preamp with the volume control on the output almost 12 years ago. And yet there still seems to be a tremendous number of misconceptions about the concept and performance ramifications of volume controls on the output instead of the input. This time the misunderstandings surround an output buffer cathode follower.

First Oil on the Chassis

Wed, 24 May 2023 00:00:00 +0000

Today I got the shop cleaned up and applied the first coat of oil to the bubinga chassis for the Source Selector Unit. (Still looking for naming suggestions, by the way.) The oil really brings out the grain. I think it will look even better than I thought it would.

What's in a Name?

Tue, 23 May 2023 00:00:00 +0000

William Shakespeare famously wrote in the play Romeo and Juliet,

What’s in a name? That which we call a rose
By any other name would smell as sweet.

So this is my quandary today. What should I “officially” name my latest project?

Metal Work and Policing Ground Loops

Mon, 22 May 2023 00:00:00 +0000

I took some time this afternoon to get the metal work completed (mostly) for the Source Selector Unit/Preamp. All the drilling is complete and everything is properly fit to the chassis. The only metal work left to do is four holes in the mounting brackets which need to be drilled and tapped. These four screws will hold the top plate in place and make swapping tubes easier.

Back to that Metal Work

Sun, 21 May 2023 00:00:00 +0000

Well, eleven days since my last post and the cedar fence is done, the garden is in, a toilet has been replaced, and a new batch of black cherry cider is in the fermenter. So I decided it was time to get back to the metal for the source selector unit.

Chassis Metal

Wed, 10 May 2023 00:00:00 +0000

I’ve been working on a whole bunch of different projects this last week. But I managed to carve out a little time to get all the chassis metal for the source selector unit cut to size, fit to the chassis, and marked for drilling.

About That Metal Work

Thu, 04 May 2023 00:00:00 +0000

I often get questions about how I design and construct my projects. One of the things I realized this morning, after receiving such a question, was that I really haven’t addressed my basic metal work and how I size all the aluminum parts I use for my chassis. So I thought I’d give a little insight into how I make these cuts and how I got to where I am today.

Time for Metal Work

Tue, 02 May 2023 00:00:00 +0000

I’ve been catching up on all my spring chores and managed to steal a couple of hours in the shop this morning. The Source Selector Unit chassis is now all sanded. I also took the time to cut and fit the aluminum for the top and bottom plates. Now my attention will turn to getting all the holes laid out and drilled on the aluminum.

Other Projects and Updates

Sun, 30 Apr 2023 00:00:00 +0000

Since my last post on the Source Selector Unit chassis I’ve been busy. Spring has finally started here with a vengeance so I’ve been tackling a few different projects. But rest assured, the chassis work will be back to the forefront soon.

Chassis Decision Made

Sun, 23 Apr 2023 00:00:00 +0000

I actually spent a fair amount of time thinking about how to dress the chassis edges for the Source Selector Unit. But after much deliberation, a couple of scrap tests, and some evolution in thought as it progressed, I believe I’ve found a solution I really like.

How to Proceed

Mon, 17 Apr 2023 00:00:00 +0000

A good friend of mine, who’s opinion I value, has made a suggestion concerning the Source Selection Unit chassis. And I’m looking for some input.

Patience Pays Off

Sun, 16 Apr 2023 00:00:00 +0000

The chassis for the Source Selector Unit / Preamp is out of the clamps. I removed the clamps, cleaned up the little bit of glue squeeze out at the joints, and gave it a light sanding. It looks fantastic.

Sometimes Waiting is the Hardest Part

Fri, 14 Apr 2023 00:00:00 +0000

Today, I did a little drilling and then got the chassis into glue up.

Some Metal Work

Thu, 13 Apr 2023 00:00:00 +0000

Before I perform the chassis glue up, I decided I wanted to get the two pieces of metal for the back drilled. This means I can make the pilot holes for the mounting screws in the inside of the back without having to work with a drill inside the glued up chassis. It’s a little thing but it makes the first assembly go that much smoother.

When It Rains, It Pours!

Wed, 12 Apr 2023 00:00:00 +0000

So I had another productive day working on the Source Selector Unit / Preamp chassis. The chassis has all the major woodworking complete and is ready for glue up.

SSU Chassis Progress

Mon, 10 Apr 2023 00:00:00 +0000

I got some time today to make grain decisions and cut some basic joinery. It finally feels like I’m making progress.

Things Are Finally Moving Forward

Sat, 08 Apr 2023 00:00:00 +0000

After a difficult and focused three months or so, I am finally getting back to my normal routines. And that means I’m returning to work on my Source Selector Unit/Preamp project. Thank you to everyone who has had patience with my absence from the website.

Wood Decision Time

Sat, 08 Apr 2023 00:00:00 +0000

Since I picked the wood for the Source Selector Unit/Preamp project yesterday, I decided to spent some time in the shop today getting the chassis pieces milled to thickness and cut to size.

Small Steps

Fri, 20 Jan 2023 00:00:00 +0000

This is just a quick post to let everyone know that I haven’t fallen off the face of the Earth. These last few weeks I have been dealing with some emergent health issues which have prevented me from getting out to my shop. But I have at least selected the wood for my Source Selector Unit/Preamp.

Time to Get Back to Work

Sat, 24 Dec 2022 00:00:00 +0000

I’ve been taking it easy the last week and a half in the run up to Christmas. But today Front Panel Express came through with the front plate for the new project. Time to get back to work.

Another Indulgence

Tue, 13 Dec 2022 00:00:00 +0000

The design of Source Selector Unit/Preamp is coming along and I think I’m going to spring for a professionally made front panel. Today I spent some time with the design software from Front Panel Express and I think the ability to provide custom engravings will be worth it.

Progress on the Source Selector

Sun, 04 Dec 2022 00:00:00 +0000

Over the last several days I’ve made some progress on the layout of the new project. This is about the point where it’s time to start looking at wood.

Meters and Transformers

Fri, 02 Dec 2022 00:00:00 +0000

A couple of quick topics today. The first is about meters and the features we (well “I”) seem to over look. The second is a quick bit of news about transformers.

Something a Little Different

Fri, 25 Nov 2022 00:00:00 +0000

About a month ago I had an exchange with a reader talking about The Purpleheart Signal Meters and modifying the project to provide multiple inputs and some gain balancing. I’ve been giving this a lot of thought in the last couple of weeks because I have the same needs. So I think this is going to be my next major project.

Happy Thanksgiving

Thu, 24 Nov 2022 00:00:00 +0000

To all those in the US, Happy Thanksgiving.

It’s a good day to reflect on all we have and spend some time with family and friends. And that’s not a bad thing to do wherever you reside.

The 6L6 "Spalted Alder" Amp

Sat, 19 Nov 2022 00:00:00 +0000

An Outgrowth of Optimization

This amplifier was a direct outgrowth of the 6L6 Optimization Study. Having performed the study of the 6L6 tubes in an SE-UL configuration, and seeing the excellent performance which could be achieved, I decided to put the data into a practical application. This amplifier is the result.

Those with sharp eyes may notice that this amplifier shares a marked external similarity with 6V6 Marblewood Amplifier. This similarity flows mostly from the layout of the top plate and the similarities in the tone and pattern of the two wooden chassis. However there are some major differences which make this a far different design overall. Also, whereas I tend to prefer to run 6L6 tubes in the Marblewood amp these days, this amplifier makes much better use of the bigger 6L6GC tubes.

The 6L6 SE-UL Amplifier Project Description

Sat, 19 Nov 2022 00:00:00 +0000

The complete project description page for the 6L6 SE-UL amplifier is now live and can be found at the following link: The 6L6 “Spalted Alder” Amp.

6L6 SE-UL Performance Numbers

Tue, 15 Nov 2022 00:00:00 +0000

I spent some time this afternoon taking technical performance data on the new amp. Unsurprisingly, the technical data is in agreement with my impressions from the excellent listening session yesterday. This amp is a solid performer and just what I wanted from the design.

The 6L6 SE-UL is Operational

Mon, 14 Nov 2022 00:00:00 +0000

The voltage checks all came out as expected, so the amplifier was put into use for an extended listening session. The most succinct description I can give is that the amplifier is clean, very fast, neutral in color, and musically powerful.

6L6 SE-UL Initial Power Up

Sat, 12 Nov 2022 00:00:00 +0000

Here’s the salient point about putting your entire amplifier design and build process on the internet for all to see. Invariably, regardless of how well everything is going, things always arise which manage to keep you humble. And today it happened again.

6L6 SE-UL Top plate installed

Thu, 10 Nov 2022 00:00:00 +0000

I got a chance to do a little work on the amp today. I managed to install the top plate on the spalted alder chassis, install the filter inductors for the power stages, connect the output transformer secondaries to the speaker terminals, and wire in the power transformer primary and indicator light.

6L6 SE-UL Wiring Is Complete - Almost

Thu, 10 Nov 2022 00:00:00 +0000

This morning I took a little time to complete the major wiring of the amplifier. Everything is in place except the B+ dropping resistor.

6L6 SE-UL Top Plate Wiring Complete

Mon, 07 Nov 2022 00:00:00 +0000

In the last few days I’ve managed to get most of the wiring on the 6L6 SE-UL top plate complete. This includes all the preposterously large power supply filter capacitors.

6L6 SE-UL Driver

Thu, 03 Nov 2022 00:00:00 +0000

I’ve managed to make a little progress on the driver stage of the amplifier. And another project is coming along well.

6L6 SE-UL Power Stage Wiring

Thu, 03 Nov 2022 00:00:00 +0000

I got a little more done on the amp this afternoon. The grid and cathode circuits on both power stages are now wired and tied into the driver.

6L6 SE-UL Wiring Progress

Thu, 27 Oct 2022 00:00:00 +0000

This is just a quick post to let everyone know that I have made some progress on the subject amp’s wiring. Unfortunately, there is a complicating factor which is slowing me down.

6L6 SE-UL Transformer Wiring

Sun, 16 Oct 2022 00:00:00 +0000

Today I took some time to install the signal ground bus and wire the transformers. But I also wanted to discuss a specific aspect of transformer wiring for the B+. I often get questions on this topic from people looking at the 6336 SET Amplifier. Let’s take a look.

6L6 SE-UL Mechanical Assembly

Sat, 15 Oct 2022 00:00:00 +0000

The paint seemed to be good and hard this afternoon. So when I got a little free time, I decided to start assembly.

6L6 SE-UL Gets Its First Wires

Fri, 14 Oct 2022 00:00:00 +0000

I’m still waiting for the top plate paint to harden. But that didn’t keep me from getting some wiring done on the chassis today.

Jumping the Gun

Wed, 12 Oct 2022 00:00:00 +0000

I know that I told myself I was going to give the paint on the 6L6 SE-UL top plate a week to harden before I started assembly. But then I thought “Hey there’s other assembly I could perform”. So that’s what I did.

A Note on Aluminum Finish

Tue, 11 Oct 2022 00:00:00 +0000

A while back in this post, “6L6 SE-UL Primed for Progress”, I mentioned that I would no longer be painting the exposed bottom plates of projects which won’t be seen. What that statement actually meant was that I would be leaving the aluminum in a bare “as delivered” finish. Or maybe with just a little steel wool polishing. But I’m now modifying that stance slightly.

6L6 SE-UL Chassis Is Ready

Mon, 10 Oct 2022 00:00:00 +0000

After many delays I have finally finished the 6L6 SE-UL chassis. The paint is still soft but I should get started mounting parts in a week or so, as soon and the paint hardens appropriately.

Spray Painting and Charge Transfer

Mon, 10 Oct 2022 00:00:00 +0000

While spray painting some metal this week a funny thing happened. During the painting session, the hair on my arms began to stand on end to the extent that it was readily apparent that something strange was happening. This led me to perform some investigations.

I Made A Change Today

Sat, 08 Oct 2022 00:00:00 +0000

On July 1st, 2018 I announced a small change to my website in this post: “A Little Change”. That change has now been reversed. As of today I have terminated this website’s association with PayPal.

Some day...

Thu, 08 Sep 2022 00:00:00 +0000

I suppose by now everyone is wondering what has happened to the 6L6 SE-UL amp project. Well, so am I. Kind of.

August Starts Off Busy

Fri, 05 Aug 2022 00:00:00 +0000

Sorry for the lack of progress on the 6L6 SE-UL. I really wanted to get the chassis finished off this week but several factors have conspired to keep me from working on it.

Back to Bare Metal

Sat, 30 Jul 2022 00:00:00 +0000

After my mistake with the finish, the top and front plates for the 6L6 SE-UL are now back to bare metal. Now begins the “Great Paint Hunt”.

That was a Mistake!

Fri, 29 Jul 2022 00:00:00 +0000

Remember yesterday when I said “There were a couple of finish blemishes which needed to be corrected. I accomplished that shortly after the above pictures were taken”? It looks like I messed up!

6L6 SE-UL In the Black

Thu, 28 Jul 2022 00:00:00 +0000

So the black finish has set up and I think it looks far better than the grey. So, again, as long as there’s no uproarious outcry, I’ll be going with the black. I think this finish ties the whole project together much better than the grey would have done.

6L6 SE-UL Grey and Black

Tue, 26 Jul 2022 00:00:00 +0000

As promised, after the primer was fully dry I took the power transformer down to my shop and put it together with the grey top on the chassis. Whereas the grey would make for an interesting look, I think I’ll like the black better. So unless there’s an uproarious outcry from the amp builders of the world, that’s the way I’ll be going.

6L6 SE-UL Primed for Progress

Mon, 25 Jul 2022 00:00:00 +0000

Sorry about the title; I couldn’t resist. I got some time today so I applied the primer to the metal for the 6L6 SE-UL amp. The primer takes 24 hours to fully dry so tomorrow I’ll place it in the amp with an Edcor transformer on top and show everyone what the grey looks like with the spalted alder.

In the Background

Sat, 23 Jul 2022 00:00:00 +0000

The fact that it’s been two and a half weeks since my last post should be an indication of just how busy I’ve been. However, I have been making progress on the 6L6 SE-UL in the background whenever I could. And now I’m happy to report that the chassis is complete and all the metal has been drilled and fitted to the finished chassis.

6L6 SE-UL Chassis Finish Update

Wed, 06 Jul 2022 00:00:00 +0000

I now have five coats of oil on the amp chassis and the color is incredible. But this finish isn’t going to be like the last couple of projects. The wood is just too different.

Spalted Alder - Notes on the Oil Finish

Sun, 03 Jul 2022 00:00:00 +0000

The second coat of oil went on the 6L6 SE-UL chassis this morning. The oil is bringing out something in the wood which was totally unexpected; color!

Finally, A little 6L6 SE-UL Progress

Sat, 02 Jul 2022 00:00:00 +0000

Yesterday I did the final metal fitting and drilled the mounting holes in the metal pieces. This allowed me to finish up all the marking and drilling on the wood chassis. This morning I applied the first coat of oil to the spalted alder. It looks very good.

I'm back!

Thu, 16 Jun 2022 00:00:00 +0000

I’ve been on vacation for the last couple of weeks but I’m back now and ready to get moving on the 6L6 SE-UL amplifier.

6L6 SE-UL Moving Forward

Thu, 26 May 2022 00:00:00 +0000

I have finally finished cutting and marking all the metal for the new amp. Now comes the long process of getting all the pieces drilled and finished.

6L6 SE-UL Raw Chassis is Complete

Sun, 22 May 2022 00:00:00 +0000

Today I finished putting the final shaping details on the 6L6 SE-UL spalted alder chassis. All it needs now is a final sanding and the oil finish.

6L6 SE-UL Chassis Wood

Wed, 18 May 2022 00:00:00 +0000

Today I made my final decisions about which piece of wood would go in each position and orientation. This amp chassis is going to be a work of art!

6L6 SE-UL Design Progress

Mon, 16 May 2022 00:00:00 +0000

This morning the power transformer for the 6L6 SE-UL arrived from Edcor. And even more importantly, I’ve got the spalted alder converted to dimensional boards. Now I just need to select what goes where and I can begin milling the chassis.

It Happened Again!

Wed, 11 May 2022 00:00:00 +0000

I just got a notification from Edcor. The power transformer I ordered for the 6L6/KT88 SE-UL Amplifier on the 2nd of May (just 9 days ago) shipped today! I thought I was going to have a lot more time to get the spalted alder chassis into shape.

A quick Note on the Purpleheart SET and 6AS7 Tubes

Mon, 09 May 2022 00:00:00 +0000

I added a note to the end of the 6AS7 “Purpleheart” SET amplifier page concerning power tube variability and their use in this amp.

Laughing At the 6L6 SE-UL Layout

Sat, 07 May 2022 00:00:00 +0000

I’ve been making an effort this morning to get my head around the internal layout of the 6L6 SE-UL amplifier. Unfortunately, I keep being stymied by the sheer physical size of many of the components.

6L6 SE-UL Chassis Decisions

Fri, 06 May 2022 00:00:00 +0000

Even though I’m waiting on a power transformer and some oversized components for the 6L6 SE-UL amp that doesn’t mean that all progress has come to a standstill. The new amp needs a chassis. And a new chassis means it’s lumber selection time.

Moving things Around and De-Cluttering

Thu, 05 May 2022 00:00:00 +0000

You may have noticed a change to the CascadeTubes home page this morning. Things have moved around a little bit.

Older Pages

Thu, 05 May 2022 00:00:00 +0000

This page contains links to the older and less frequented pages from CascadeTubes history.

Dummy Speaker Load

This is a simple piece of test equipment to help facilitate the testing of power amplifiers. Although simple, I use this piece of equipment with every amplifier I build.

Volume Control

This is a page discussing the building and use of a simple standalone volume control from a stepped attenuator.

Brassboard Prototypes

This is an article on the types of prototyping and the good things which can be learned from “near final configuration” or brassboard prototypes.

The "Purpleheart" Signal Meters

Thu, 05 May 2022 00:00:00 +0000

Something A Little Different

When I posted The 6AS7 Purpleheart" SET amplifier page, I could not have anticipated the interest in the companion unit to this amplifier. So great has been the interest in this little unit that I decided to provide this signal meter component it’s own project page.

This is my first foray into using these ubiquitous little Vu meters. In the past I had always hesitated because of the meters’ unique driving requirements. The issue really lies in the standard for Vu meters in general. Mechanical meters have to be time averaging and this is usually accomplished with a very specific spring/mass balance. To properly drive this balance takes a little power. As such, these meters have an input impedance of approximately 7500Ω. They also assume a certain amount of drive capacity on the signal line.

Switching Gears is Hard on the Clutch

Tue, 03 May 2022 00:00:00 +0000

The gear switching I’ve been doing on this rainy afternoon has been putting the 6AS7 “Purpleheart” SET in the “finished” column of the ledger and getting to work on the upcoming 6L6 SE-UL amp. And I’ve already run into a delay.

The 6AS7 "Purpleheart" SET

Sat, 30 Apr 2022 00:00:00 +0000

A Long Time in the Making

Ever since completing the 6336 SET back in 2017 this amp has been bouncing around in my head. The big SET has a lot going for it, however there is a high price to be paid in both amplifier infrastructure and operational heat. And that price is basically for a handful of dBs (≈4.4dB in the end) difference in peak power performance. I had developed a design for a 6AS7 SET driven by a 12AX7 several years before but was never happy with that design. However, once I developed the high voltage swing driver for the 6336 SET, it opened up all kinds of new possibilities.

6AS7 SET "It's Alive!"

Thu, 28 Apr 2022 00:00:00 +0000

Yesterday, after setting the B+ and installing the power supply dropping resistor, I tried out the 6AS7 SET. To say that I am pleased would be an understatement.

6AS7 SET is Completely Wired!

Wed, 27 Apr 2022 00:00:00 +0000

I first announced this SET on September 18th, 2020. It’s only taken me about 19 months to get to this point. To be fair, that 19 months was fairly eventful, including both my retirement and much of the COVID madness. But tomorrow, the slow methodical process of testing can finally begin.

Old Dog, New Tricks

Tue, 26 Apr 2022 00:00:00 +0000

Although sometimes it may take a little disturbance to the system, as it turns out, you can teach an old dog new tricks.

More SET Progress

Sat, 23 Apr 2022 00:00:00 +0000

With all the distractions this week, I’m not quite as far along as I would have hoped. But all the top plate wiring is done, the power supply sections are complete, and the 6AS7 power stage is complete.

New Content

Fri, 22 Apr 2022 00:00:00 +0000

I just posted the project page for the 12AU7 “Color” Preamp which I completed a couple of months ago. Why don’t you go check it out.

The 12AU7 "Color" Preamp

Fri, 22 Apr 2022 00:00:00 +0000

A Simple Preamp with a Specific Goal

The idea for this preamp has been floating around in my head for almost ten years. Ever since I built and posted about the “Universal” Preamp there has been a lot of discussion about a buffered preamp for adding tube color to lower input impedance solid state amplifiers. This discussion arose because the “Universal” Preamp, with its higher output impedance, is really not well suited for driving solid state amplifiers. So this winter I finally decided to tackle this project.

SET Wiring Coming Into Focus

Wed, 20 Apr 2022 00:00:00 +0000

I really haven’t had as much free time this week as I thought I would. But, in spite of other tasks taking priority, I’ve managed to get the iron for the SET all wired into the top plate.

Good Progress in 6AS7 SET Assembly

Tue, 19 Apr 2022 00:00:00 +0000

I managed to make good progress on the assembly of the 6AS7 SET today. In addition to getting all the hardware and iron mounted in the chassis and on the top plate, I’ve actually started wiring.

A Little Progress

Thu, 14 Apr 2022 00:00:00 +0000

I managed to eke out a little time to work on the 6AS7 SET top plate this afternoon. I didn’t get a lot done but at least I’ve finally started.

6AS7 SET Assembly Begins

Tue, 12 Apr 2022 00:00:00 +0000

After many delays and distractions I have finally finished the 6AS7 SET chassis and have begun assembly.

Getting Organized and About Those Jigs

Tue, 05 Apr 2022 00:00:00 +0000

I currently have a couple of major projects on the workbench and a few other minor tube circuit investigations underway. When this happens I find myself pulling things off of shelves, moving other things around, and generally creating quite the mess until I’m having problems finding just about anything. When this happens I generally step back and take some time to get everything organized again. But this time, I wasn’t quite prepared for what I found.

Progress on Several Fronts

Sat, 02 Apr 2022 00:00:00 +0000

It’s been a productive few days. Two different amp projects are coming along nicely and today I’ve reached a milestone.

Volume Controls and High Frequency Response

Thu, 31 Mar 2022 00:00:00 +0000

These last few days I’ve been working on the driver stage and overall schematic for the new 6L6 SE-UL amplifier. While drawing up the schematic yesterday, I inserted a 250kΩ volume control at the input without much thought. While performing some preliminary analysis, I realized my mistake.

6AS7 SET Chassis Is Almost Complete

Mon, 28 Mar 2022 00:00:00 +0000

For the last few days I’ve been applying oil to the SET chassis. It now has four coats of oil, cured and buffed out. There’s only one decision left for the chassis.

Everyone Makes Mistakes

Mon, 28 Mar 2022 00:00:00 +0000

Today I was once again reminded of the perilous state of human fallibility and the risks of personal hubris. The cost of today’s lesson? One ruined KT-88. And a little smoke in the office.

Overlapping Projects and Getting Things Done

Sat, 26 Mar 2022 00:00:00 +0000

This afternoon I’ve been working on another amplifier project. This particular one is the 6L6 SE-UL for which some readers have been looking since I published my Optimization of the 6L6 SE-UL page back in March of 2019. I recently realized that it had been three years since I published that data set and that it was probably time for me to get the project started. So this afternoon I’ve been investigating driver stages for the amp.

The Morning SET Swap

Sat, 26 Mar 2022 00:00:00 +0000

This morning as I sat down in my office to check email and the like, I looked over at the amp in the corner of the room and made a snap decision. It was time to perform a SET swap.

6AS7 SET Finally Starts to Move Forward

Thu, 24 Mar 2022 00:00:00 +0000

It looks like the weather has finally broken here at CascadeTubes and spring has arrived. Yesterday, the 6AS7 SET chassis got its first coat of oil. The purple heart used for this chassis is definitely much deeper in tone than that used on the The 6DJ8 Headphone Amp.

Line Level Isolation Transformers - A Lesson Learned

Sat, 19 Mar 2022 00:00:00 +0000

About a year ago my television display died and I was forced to buy a new TV. I had been using the Lacewood V2.0 amplifier for the sound system and, when I plugged in this new TV, it formed a bad ground loop with the amplifier, introducing a nasty hum. This was not an insurmountable problem. I simply dug through my parts closet until I found a little line isolator I had built about a decade previous for some project I was working at the time. I installed this isolator and the problem went away. But that’s not the end of this story.

The Dual Triode Test Station is Complete

Fri, 18 Mar 2022 00:00:00 +0000

I took some time this week to get several coats of oil on the chassis for the Dual Triode Test Station. Even though I’ve already used it for the mystery tube investigation and to compare some 12AU7s, it’s good to have it finally complete.

Mundane Tasks for the Vacuum Tube Enthusiast

Mon, 14 Mar 2022 00:00:00 +0000

I spend a lot of time experimenting with various vacuum tubes circuits. It is a past time which I really enjoy. It also gives me an outlet for my creative tendencies when the workshop is too cold to make custom furniture (and amplifier chassis). As a consequence I have amassed a fair amount of test equipment and miscellaneous cables, adaptors, probes, and other odds and ends over the last decade or so. And regardless of the fact that I want to concentrate my attention on my vacuum tubes, sometimes it’s the other things that demand my attention.

A Tale of Two Tubes - New vs. Old

Sun, 13 Mar 2022 00:00:00 +0000

Back in November, in my post concerning Tubes and Tube Testers, I talked about how I was not really a fan of generic tube testers. In that post I sited a statement from the RCA “Receiving Tube Manual”, RC-30, about testing tubes.

The tube tester cannot be looked upon as a final authority in determining whether or not a tube is satisfactory. An actual operating test in the application will give the best possible indication of a tube’s worth.

So I thought that as a simple demonstration I would collect some data from a couple of tubes; one new and one rather ‘used’. The results are really kind of surprising.

Identifying a Mystery Tube

Thu, 10 Mar 2022 00:00:00 +0000

This has happened to most of us at some point or another. You come upon a tube with no markings whatsoever mixed in with a bunch of miscellaneous tubes. Or, like I just did, you get a “lot” of tubes from a reseller and most are marked but a few are wiped clean. But how does one go about positively identifying the mystery tube? Especially with the numerous types of 7 and 9 pin miniature tubes in existence this can seem to be a rather daunting task. However, just like a game of “20 Questions”, it is actually simpler than one might think.

Why Not to Use 6V6s As Preamps

Wed, 09 Mar 2022 00:00:00 +0000

This is a topic that rears its head periodically on vacuum tube forums and discussions. Just a couple of days ago I was reading a forum thread on preamps and someone threw out the suggestion of using a triode strapped 6V6 as a preamp tube. Now this is nothing new. I’ve been hearing this suggestion, on and off, for at least ten years. But using a triode strapped 6v6 (or any beam power tube) as a voltage amplifier is a poor idea which simply doesn’t hold up to technical scrutiny.

Switching Amps and Getting My Brain to Pay Attention

Mon, 28 Feb 2022 00:00:00 +0000

Now that the color preamp is done (knock wood), I’ve been trying it out on different amplifier and speaker combinations. But there is a little issue. Unknown to most people is that your brain can really only hold onto an unadulterated memory for a minute or so at the very longest. Most of the time you’ve got less than about 30 seconds. After this interval your brain starts throwing out what it considers to be extraneous information leaving only impressions. And this is a big issue when attempting to make subjective comparisons.

Not Quite Done

Sat, 26 Feb 2022 00:00:00 +0000

There are a variety of sayings, axioms, proverbs, or quips which could apply to me this afternoon. A few which come to mind include:

“How wayward the decrees of fate are” - Vanitas Vanitatum - William Makepeace Thackeray

or this one:

“Pride goeth before destruction, and an haughty spirit before a fall” - Proverbs 16:18

or just the simple axiom:

“It ain’t over till it’s over” - Yogi Berra

In any event, it would seem that “Final Chapter” or no, I have one more post concerning the Color Preamp.

The 12AU7 "Color" Preamp - The Final Chapter

Fri, 25 Feb 2022 00:00:00 +0000

So I decided today that I really needed to close the book on the color preamp. This means that I couldn’t just prototype a new buffer and leave it at that. The preamp needed an end-to-end test in it’s final design configuration. So that’s what I did. The results were even better than before.

The 12AU7 "Color" Preamp with Improved Buffer

Tue, 22 Feb 2022 00:00:00 +0000

Lots of work has been going on the last couple of days working on an alternate buffer design for the 12AU7 “Color” preamp. As readers should know, I was not particularly pleased with the performance of the previous buffer circuit. It was bottoming out at too low a voltage. Now however, I have a simple change which yields much better results.

The 12AU7 "Color" Preamp is Complete

Mon, 21 Feb 2022 00:00:00 +0000

This afternoon I completed the “color” preamp and tried it out. I am very happy with the results.

Circuit Reuse and Latent Design Issues

Sun, 20 Feb 2022 00:00:00 +0000

The “Color” preamp has been checked out on the test bench and everything is working per design. Bias points are good and the gain stage is operating exactly as designed. However, the buffer design I used was from a different project, and it operates differently in this project than the last one.

The Color Preamp is Fully Assembled

Fri, 18 Feb 2022 00:00:00 +0000

I had thought that the coupling capacitors I ordered on Tuesday would not arrive until this Saturday. However, the gods of DIY decided to smile down upon me and the capacitors showed up in today’s mail delivery. In my opinion, two days from order to delivery is exceptional. I spent some time this afternoon with a soldering iron in hand and the Color Preamp is now fully assembled.

The Color Preamp Tales of Woe

Tue, 15 Feb 2022 00:00:00 +0000

As you may know I’ve been waiting on components to finish my “Color Preamp”. I thought that I’d have my output coupling capacitors by now, but I was mistaken. It seems that my parts supplier, after promising to get the parts right out to me, spent three days trying to find the parts in their warehouse, then sent me a refund. But I thought I’d outsmarted them.

Component Tolerances & Modern Manufacturing

Sun, 13 Feb 2022 00:00:00 +0000

Since I’ve been at a standstill waiting for parts, I’ve been going over my parts supply and getting things organized again. It seems we’re all constantly working against entropy. While doing this, my bagged and sorted capacitors reminded me of a short article I wrote back in 2013 about component tolerances. I’ve decided to reprint it here for reference.

More Progress and a Work Stoppage

Thu, 10 Feb 2022 00:00:00 +0000

I made significant progress today. Most of the signal stage wiring is done. I could finish it up in about half an hour, but there are two little blockages in my path; one due to a supplier problem, one due to me.

Progress on the "Color" Preamp

Tue, 08 Feb 2022 00:00:00 +0000

I’ve been working on the color preamp over the last few days as I’ve had time. My volume control and output capacitors are supposed to arrive today so it shouldn’t take too much longer to finish it up. However working inside the small chassis is a challenge.

Quick Project for the Preformed Chassis

Sun, 06 Feb 2022 00:00:00 +0000

Since I’m still waiting for appropriate weather to finish the 6AS7 SET chassis, I’ve been making progress on a small project for the aluminum chassis from the last post. I decided to put together the “Color” preamp from the post a few days ago. This project will make use of one of the Hammond discount power transformers about which I posted a couple of weeks ago. It’s coming along well, but VERY slowly.

Amp Chassis Options

Fri, 04 Feb 2022 00:00:00 +0000

While waiting for appropriate temperatures to paint and apply oil finishes, I’ve been working on a simple preamp project. It’s only a handful of parts and to avoid complications with finishing a handmade chassis, I decided to use a preformed aluminum project box I had sitting on my shelf. I quickly regretted that decision.

Tube "Color" Preamp for Solid State Amplifiers

Mon, 31 Jan 2022 00:00:00 +0000

For a while now, ever since the “Universal Preamp” was posted on the site, I’ve been getting steady requests for a good tube preamp to provide some color to solid state amplifiers. My initial answer to this problem was to design a good quality cathode follower for the Universal Preamp. There was one problem, the volume control.

Progress on the Test Jig

Sat, 29 Jan 2022 00:00:00 +0000

Ignoring the wood chassis for the time being, I made significant progress on the triode test jig today. I just thought I’d post a quick update. Parts are now mounted and some wiring is underway.

At the Assembly Crossroads

Tue, 25 Jan 2022 00:00:00 +0000

I’m working on two projects simultaneously right now; the 6AS7 SET and the Triode Test Jig. In the last couple of days I’ve made progress on both. However now I appear to be at an impasse.

Much Better Patina This Time

Sun, 23 Jan 2022 00:00:00 +0000

It’s been a tense couple of days waiting for the patina to set on the 6AS7 SET top plate. But I just placed the copper on the chassis and it looks great!

That Didn't Go as Planned

Sat, 22 Jan 2022 00:00:00 +0000

Regardless of how much planning you do and how many test runs you accomplish, sometimes things simply don’t go as planned.

Preamp Transformer

Fri, 21 Jan 2022 00:00:00 +0000

As everyone who’s tried to buy one knows, power transformers for tube projects can be expensive. Even small transformers for small projects. But today I stumbled on a great deal for a small preamp power transformer made by Hammond.

The SET Moves Forward

Thu, 20 Jan 2022 00:00:00 +0000

With the return of some more normal weather here I got the chance to work on the SET chassis today. Specifically I got the bare copper plates chemically treated for the patina for which I was looking. They look good. Or, more accurately, they look just the way I imagined when I first thought of doing this. I’m very happy with the results.

About that Volume Control

Mon, 17 Jan 2022 00:00:00 +0000

Since I first introduced the concept for the “Universal Preamp” over ten years ago on the DIYAudioProjects forum, there has been almost constant discussion of my decision to place the volume control on the output of the preamp. I have been asked questions about it numerous times over the years. I have also had some “spirited discussions” with some who vehemently disagree with that design decision. Well, I thought it was high time to explain that decision once and for all, and to discuss exactly what this configuration means for preamp performance and output impedance.

Toroids and "Shorted Turns"

Fri, 14 Jan 2022 00:00:00 +0000

As I was going through some things today I stumbled upon an email discussion I had recently on the topic of toroids (i.e. toroidally wound transformers and inductors) and shorted turns. Given the popularity of toroids, and amount of misinformation floating around on the internet on the topic of shorted turns, I thought that a short discussion of the phenomenon was in order.

Triode Test Jig Progress

Thu, 13 Jan 2022 00:00:00 +0000

The weather has finally returned to normal here and I got to spend a little time in my shop today. I decided that I wanted to be able to finish the base of the SET and my new triode test jig at the same time. So I needed to get going on the test jig base.

Quick Note on Contents

Sat, 01 Jan 2022 00:00:00 +0000

I have added a side bar widget on the Blog page labeled “ARTICLES OF NOTE”. I decided that rather than having links floating all over the posts and comments, when I found something of interest I’d post the link in this block.

The first item is a web page from the Lampizator site discussing Audio Heresy. I found it fairly humorous.

Talking about SETs

Thu, 30 Dec 2021 00:00:00 +0000

With my shop temperature hovering around 38°F (≈3°C) and with the outside temperature hovering around 20°F (≈-7°C) I though that today might be a good time for a little “inside” amplifier discussion. And today’s discussion is about SETs; BIG ONEs.

A 6AS7 SET Option

Tue, 21 Dec 2021 00:00:00 +0000

One more thing concerning Front Panel Express; with a tie in to the SET project. Just as an experiment, last night I opened Front Panel Designer and duplicated my 6AS7 SET top plate design. Now that I’m familiar with the software it took less than an hour to complete.

The "Indulgence"

Sun, 19 Dec 2021 00:00:00 +0000

When I talked about designing the Dual Triode Test Jig in the “More on Tube Testing” post I mentioned an indulgence. Well the results are in.

Expanding Horizons

Mon, 13 Dec 2021 00:00:00 +0000

We’ve had a chilly rain/snow mix today at CascadeTubes so it’s a little too cold to work on the SET chassis in my unheated shop. Instead I’ve been thinking about my new triode test jig and have been going over the tube list that it covers. There are lots of tubes on the list with which I am not intimately familiar so I’ve been pulling data sheets and doing some investigations. And I’ve received some pleasant surprises!

More on Tube Testing

Thu, 09 Dec 2021 00:00:00 +0000

The discussion on tube testers and their usefulness (or not) got me thinking about my own tube testing needs and how I go about it. I already have a solution for octal power tubes with the 7S base pinout which I’ve mentioned before. But what about those ubiquitous signal triodes I seem to use in almost every project? What should I do about them?

Update on the SET Chassis

Sun, 05 Dec 2021 00:00:00 +0000

So I’ve been playing with the copper tarnish/patina process and I think I’ve got it figured out. After doing lots of small parts with various approaches I’ve learned enough to start the amp pieces. Among the things I’ve learned is that the washing process both before immersion in the chemical bath and after tarnishing while washing off the chemicals is very important. I’ve also learned that an even buff with a steel wool is better than taking the copper to a high gloss shine. And finally, the initial tarnish is very fragile. After doing the bath and letting the piece dry, it really should be left sitting in the open air for between three and five days. After this, the oxide layer toughens up and it can be handled and clear coated.

Copper Patina for the 6AS7 SET

Wed, 24 Nov 2021 00:00:00 +0000

As I mentioned back in June, I have been looking at different finishes for the copper portions of my 6AS7 SET amp. At that time I had mentioned that I was interested in a “patina” type finish for the copper. I learned that to many people copper patina means green tones, blue corrosion, and wild colors. I was looking for something more like a tarnished penny look. Something that would make the unit look more like an older piece of equipment. Unfortunately this was to be more involved than I first imagined.

Tubes and Tube Testers

Sat, 20 Nov 2021 00:00:00 +0000

I get a lot of questions from people looking at my website. Most questions are about the posted projects or requests for recommendations for test equipment. However a topic which comes up regularly is about vacuum tube testers. The questions range from simple a “Should I buy one?” to complex requests for information on types, operation, “accuracy” and the ever present question “Are they worth it?”. Unfortunately, the topic is actually much more complex that most people realize.

One Last SET Driver Check

Mon, 15 Nov 2021 00:00:00 +0000

I took some time yesterday to perform a performance check on the driver for the 6AS7 SET. As some may recall, this driver was developed and prototyped back in 2015, and brass boarded in 2016, as a driver for the 6336 SET Amplifier. In the 6336 design it uses a 300v B+ to produce a swing of 82V peak to fully drive the big triode. However, in the unique power supply topology of the 6AS7 SET, there are some additional considerations.

A Couple of Bad Months

Thu, 04 Nov 2021 00:00:00 +0000

To anyone trying to get in touch with me for the last couple of months, I apologize if I didn’t get back to you. It’s been a couple of bad months.

About That Bias Point

Thu, 05 Aug 2021 00:00:00 +0000

Back in June, in the Competing Priorities post when talking about the 6AS7 SET, I made the following statement:

I also had another idea this morning which may lead to a little more prototyping work to check out a theory I have (another potential delay). But if the experiment turns out well, I may move bias points around a little on the 6AS7.

Well, I spent this morning with some prototype circuits and a stack of tubes investigating the bias points for the 6AS7 SET power stage. And I learned a couple of important lessons.

Another Option

Sat, 24 Jul 2021 00:00:00 +0000

This last week I was thumbing through my very dogeared copy the RCA RC-30 Receiving Tube Manual. I was not looking for anything in particular but just browsing and a data sheet for a particular tube caught my eye; the 6DQ5 Beam Power Tube. The only description was “Glass octal type used as horizontal-deflection amplifier in color and black-and-white television receivers”. As I began looking through the specifications I began to wonder how I had missed this tube up to now.

Sometimes Life Gets In The Way

Wed, 14 Jul 2021 00:00:00 +0000

It’s been a month since I posted about the new SET and I just thought I’d let everyone know that I haven’t forgotten about the project. The truth is, as the title says, life has gotten in the way. Most specifically, this month I started on a major project; I’m helping my daughter build a house.

"Pecking" at the SET

Tue, 15 Jun 2021 00:00:00 +0000

“Peck”. This is a term with which I don’t expect most tube amp builders to be highly familiar. However, it is a term that is exceedingly important to my work this morning on the 6AS7 SET amplifier. Let me explain.

Competing Priorities

Wed, 09 Jun 2021 00:00:00 +0000

I’m now just shy of ten weeks into my new routine and there are a lot of projects vying for my time and attention. This situation has made it difficult to make serious progress on my 6AS7 SET project.

About that SET...

Tue, 27 Apr 2021 00:00:00 +0000

It’s been several months since I’ve talked about my new 6AS7 SET and my guess is that some folks are wondering what’s happening. Don’t worry, it’s still in process. However there are some extenuating circumstances associated with the amp’s delay. Let me explain.

In Praise of the "Album"

Sun, 31 Jan 2021 00:00:00 +0000

For me, it really started about six years ago. I had been using an iPod for a while before that, but the real transition took place sometime in 2015. I had been notified that I was moving cross country for work and things were getting boxed up and ready. All my CDs and vinyl were carefully packaged up for the move. I was left with an iPod and my computer for playing music. That was when I started my slide into bad musical habits.

A Different Twist

Mon, 18 Jan 2021 00:00:00 +0000

I often get emails and pictures from builders that have built some of the projects I’ve posted here at CascadeTubes. I like seeing all the different ways that people have taken what I provided and modified it to put their own spin on the project.

Back to Work

Sat, 09 Jan 2021 00:00:00 +0000

The Christmas break saw me very busy with tasks other than amp building. So the new SET is a little behind schedule. In spite of it supposedly being a “quiet” Christmas with just immediate family, I ended up tackling several small projects which I had been putting off and I helped my daughter move. And of course I was back at work this week as well. Now that doesn’t mean that I got nothing accomplished, it just means that things are progressing slower than anticipated. This is where I’m at:

Amps, Kits, PCBs, and DIY

Sun, 20 Dec 2020 00:00:00 +0000

I just wanted to touch on the subject topic this afternoon. I have recently been helping out an individual who is assembling an amplifier with a purchased PCB. And he’s having a few issues.

The New SET is Finally Set

Thu, 17 Dec 2020 00:00:00 +0000

No, really, it is. I swear. This time I’m sure!

Bump In The Road

Sat, 12 Dec 2020 00:00:00 +0000

So I took some time the other day and got all the purple heart planed to thickness and ready to go for the new SET amp. Then, when I was checking all the layouts, I discovered a problem.

About Tube Books

Tue, 24 Nov 2020 00:00:00 +0000

I often receive some variation of the question “Are you going to write a book?”. While the answer to this query is almost universally “no”, I thought I’d take the time to highlight what I think are some of the best books available on tube amplifier design and why I think so.

Finally, A Decision

Sat, 14 Nov 2020 00:00:00 +0000

Well, it took a while but I’ve finally settled on the wood for the new amp chassis. I had narrowed the decision down to either the Purple Heart as I used in The 6DJ8 Headphone Amp or the Wenge that I used in the Dummy Speaker Load. So I took a careful look at both previous projects.

Design Details

Wed, 04 Nov 2020 00:00:00 +0000

I have been doing internal layout work and making some design decisions concerning the new SET amplifier. I have also been looking at different materials and I decided that I wanted to make the top plate holding the transformers and tubes of brushed copper. While this is an simple decision to make at this point, it raises the issue of what wood to choose for the chassis frame.

That "Other" Project

Sat, 24 Oct 2020 00:00:00 +0000

I have been working on the new SET chassis design but that’s not all I’ve been doing. This morning I got a little surprise when I checked on my sump pump under the house. It’s starting the rainy season here and I wanted to make sure everything was ready to go. Unfortunately, I found myself replacing a GFCI outlet and the sump pump that had failed and taken the outlet with it. Since the morning was shot, I decided to finish up a couple of other little projects this afternoon. Last week I mentioned another project, the portable class D amp. We’ll, I took a little time this afternoon to finish off that one.

SET - Step One

Sun, 18 Oct 2020 00:00:00 +0000

The arrival of the output transformers today gave me the impetus to finalize a few things in the 6AS7 SET design. So now I have a complete schematic with all the important information noted on it.

No More Excuses

Sat, 17 Oct 2020 00:00:00 +0000

One simple sight that really gets me excited is to see that very heavy box sitting on the front porch. Today, the output transformers for the 6AS7 SET amp arrived from Edcor.

Other Projects

Sat, 17 Oct 2020 00:00:00 +0000

There is one thing about vacuum tube amplifiers that sometimes gets in the way. They are not exactly what one might call portable.

New SET Coming

Sat, 19 Sep 2020 00:00:00 +0000

As I discussed in my last post, there is a new SET amplifier on the horizon. This SET will sit midway in power and performance between the little SETs (6CY7, 6CY7 V2, and the 6EM7) and the big 6336 SET Amplifier.

Design Decisions

Sun, 13 Sep 2020 00:00:00 +0000

So with the 6CY7 V2.0 Zebrawood amp finished and my 6L6UL project on the back burner, I’ve been working on a new SET amplifier. I have been thinking about an amp somewhere between my small SETs and the big 6336 SET amp. But I’ve run into a hiccough.

A/B Testing

Mon, 07 Sep 2020 00:00:00 +0000

I was arranging some things today in preparation for an event this evening and happened to have a little Class-D amp in my office that I normally use in my wood shop. So I decided to try a little A/B testing.

The 6CY7 V2.0 "Zebrawood" Amp

Sat, 05 Sep 2020 00:00:00 +0000

A Long Lineage

This amplifier has a long design evolution history. This first prototype iteration of this design first played music on April 17th, 2011. I designed it as an outgrowth of a tube forum discussion on “spud” amplifiers (i.e. single tube amplifiers). I had stumbled across this tube in the RCA Receiving Tube Manual RC-30 and it looked like a promising candidate for a low powered spud amplifier. Here is the first prototype complete, with power transformer and tube rectification.

"Experts"

Wed, 02 Sep 2020 00:00:00 +0000

So I was reading one of the tube forums recently and I saw an amp builder who, when talking about his latest build, said “To my ears sounds nice but I am not an expert”. Now I read or hear variations on this theme all the time. And frankly, it upsets me greatly.

Introducing the 6CY7 Zebrawood

Tue, 18 Aug 2020 00:00:00 +0000

So it’s been a while since I first grabbed the plank of Zebrawood in my shop and envisioned it wrapped around an amplifier. That was June 13th. Here it is a little over two months later and I now actually have a functioning amplifier. I have to say I’m pretty happy with how it turned out.

Slow Progress

Sun, 09 Aug 2020 00:00:00 +0000

As some may already know, I’ve been working on a new version of the 6CY7 amplifier. There is a new chassis specifically designed for this amp and some circuit changes to improve performance. But here’s the issue, I can’t seem to get much done. Let me explain.

A Small Change

Sun, 19 Jul 2020 00:00:00 +0000

I have made a small change to the website which I hope will be helpful.

Waiting for Paint

Fri, 17 Jul 2020 00:00:00 +0000

So I’ve had the chassis and metal done for the 6CY7 V2 amp since the 4th of July. It has now been a full 13 days and… the paint is not yet fully cured. It is hard for me to remember it ever taking this long for a semi-gloss enamel on metal to cure hard enough to begin assembly work. Obviously the manufacturer has changed the solvent makeup of the paint I use. Time to find another manufacturer. In the mean time, I’ve been working on other things.

Tube Tools

Fri, 10 Jul 2020 00:00:00 +0000

Like everyone else all over the world, for the last four months I’ve been working from home and limiting my trips out out of the house. But the situation these last four months has not been entirely unwelcome (except of course for people getting sick). For one thing, the view from my home office of trees and mountains is immensely better than the windowless building in which I was working. And for another thing with no commutes and flexible schedules, I have gained several additional hours in my day for doing things I want to do. With all I new found time, I did what any responsible technical person would do in such uncertain times. I’ve been teaching myself some new skills.

Wood and Metal

Thu, 02 Jul 2020 00:00:00 +0000

Well, the new version of the 6CY7 amp is coming together. The wood for the amp has gone from a raw 11″ x 58″ plank of Zebra Wood {Microberlinia brazzavillensis} into a finished amplifier chassis complete with four coats of Tru-Oil finish. I think it looks pretty good.

Change is Good

Sat, 27 Jun 2020 00:00:00 +0000

I want to start by rolling the clock all the way back to March 6th of this year. It was Friday and I had just returned from a business trip the night before. That afternoon (Thursday) my employer had decided that everyone was to start working from home immediately. Not wanting to try performing complex engineering tasks with only a laptop screen, I immediately ordered two nice high definition 24" monitors. But the question was where to put them. The “answer” was, on my office desk where I usually do tube work, including prototyping and assembly. This gave me a good spot to do my job, but with two large monitors and their ample stands, it left little space for power supplies, oscilloscopes, signal generators, and other such trappings of my vacuum tube amplifier work.

A Productive Day

Sun, 14 Jun 2020 00:00:00 +0000

So I usually have multiple amp projects going on at any one time. There is a rather large project that I’ve been working on but it’s going rather slowly and I was hungry to make some progress on something. As such, I decided to tackle a smaller project I first prototyped in 2011 and that has been on hold since 2015. I spent the better part of today turning an 11" x 58" plank of Zebra Wood {Microberlinia brazzavillensis} into an amp chassis.

Revisiting Past Endeavors

Sun, 17 May 2020 00:00:00 +0000

So, I was sitting here on this rainy Sunday morning going through some amplifier designs and looking through my stash of tubes and various amplifier building supplies. While standing there looking at the shelves of vacuum tubes, transformers, and various piece-parts, my eyes drifted up to an amplifier sitting on the top shelf. It was my 6AS5 µ-power UL amplifier documented here. But why was the little amp sitting on a shelf collecting dust? Then I remembered.

Single Purpose Jigs

Sat, 02 May 2020 00:00:00 +0000

For those that are paying particular attention to my amp builds it will come as no surprise that I think the #44 and #47 (0.9 and 0.5 candela respectively) indicator lamps are a little bright to be used on tube amps. I just think that they tend to overpower the look of the amplifier when the room gets dim. However, as these lamps are ubiquitous, it pays to use them in our builds. So, on the 6DJ8 Headphone amp and the 6EM7 vertical amp I included a small adjustment potentiometer to tame these power indicators. And on the Marblewood amp, I chose a fixed 25Ω 1W resistor to dim the indicator.

Grounding Philosophy

Mon, 13 Jan 2020 00:00:00 +0000

I keep getting questions about amp grounding so I thought I would consolidate some of my previous notes on the subject. The first is a reprint of a forum post I made back in 2013 on the DIYAudioProjects Forum.

Warning: It has been brought to my attention that some people reading this post mistakenly believe that I am advocating the override, disconnection, or elimination of the safety ground (or bonding) connection in some pieces of equipment. This is not correct! The safety ground or bonding requirement for every piece of equipment is a firm requirement. At no time should any signal cable or independent wire be expected to fulfill the safety ground requirement for any piece of equipment. The process of “ground lift” is simply to provide a different signal ground reference in a piece of equipment.

Optimization of the 6L6 SE-UL

Wed, 20 Mar 2019 00:00:00 +0000

Introduction

So this is the second of my ultra linear bias optimization studies. This one is for the 6L6 power pentode and, like the last one for the 6V6, is done for the 5kΩ plate load case. Since doing the 6V6 assessment almost three years ago, I decided that I needed a more robust way to perform the task. So I built out this simple jig.

This jig is basically the same, electrically, with the setup I used for the 6V6 investigation. The real difference is that this makes the process simpler and safer. Here is the schematic showing what’s included in the jig.

Singleton Power Tubes

Sun, 03 Mar 2019 00:00:00 +0000

Being a proponent of single ended topologies, I am constantly on the lookout for singleton power tubes. Since I’m working on designs with all single ended signal chains, things like matching and bias points as less important to me than tubes which test strong and are reliable. One source containing lots of singleton “New Old Stock” and “Used” power tubes is Ebay. Often I can get a single power tube for far less than buying from one of the more established vacuum tube business on the web. But I have begun to wonder about whether these are really such a great deal after all.

UL Optimization Revisited

Sun, 24 Feb 2019 00:00:00 +0000

Ever since I completed the Optimization of the 6V6 SE-UL I have been saying that I was going to do the SE-UL optimization process for more tubes. So yesterday I finally started to make plans.

That Was Surprising

Sat, 26 Jan 2019 00:00:00 +0000

I just got a serious lesson in room acoustics. Please let me explain.

Distortion Misunderstood

Tue, 22 Jan 2019 00:00:00 +0000

I just had a little tussle with with the local blatherskites over at one of the less hospitable internet audio forums. The actual subject of the exchange is unimportant. However it got me to thinking about distortion and how today the concept of distortion has become seriously misunderstood.

Loudness?

Thu, 08 Nov 2018 00:00:00 +0000

Anyone who has taken a look around this site should soon realize that I really like my low power amplifiers. What this means is that most of my listening is at lower volume levels. Now the only problem with this is that the sensitivity of the human ear to different frequencies is dependent on volume level. So at low volume levels, the ear has relatively poor sensitivity to both low and high frequencies. And the quieter the music gets, the worse the mismatch becomes. Traditionally the answer to this conundrum was the humble “loudness” control.

Interesting Discovery

Mon, 02 Jul 2018 00:00:00 +0000

So I was sitting down today to prototype a new 6SN7 preamp with a buffered output. As I was getting equipment arranged and pulling components I looked over at my dedicated prototyping station and something didn’t look right. As I looked more closely something jumped out at me that was unexpected and frankly, more than a little surprising.

A Little Change

Sun, 01 Jul 2018 00:00:00 +0000

If you look over to at the top of my blog page you’ll notice a little change. At the top of the sidebar is a little yellow PayPal button readers can use to donate to CascadeTubes. There is also one at the base of the home page. And I thought that after all these years, a little explanation was in order.

Tube Sound - Power Stage Topology

Sun, 18 Mar 2018 00:00:00 +0000

In one of the page comment sections, Dave K asked this particular question:

You have both SET and UL pentode amps, from the listener’s standpoint, what are the audible differences in sound between the two types?

From a tech standpoint, I know that triode = even harmonic distortion, pentode = odd harmonic distortion UL pentode = ??

And this was the simple answer I provided:

Amp Layout Tools and Ideas

Sun, 11 Mar 2018 00:00:00 +0000

A big part of building custom vacuum tube amplifiers is layout. Even when the schematics are finalized and parts are ordered (and even delivered) the preparatory work is not over. With this phase comes the arranging and rearranging of transformers, tube sockets, potentiometers, switches, jacks, terminal strips, and all the other miscellaneous parts that make up the final amplifier. And this is where some simple quality tools can make all the difference.

The 6V6 Marblewood Amp

Thu, 08 Mar 2018 00:00:00 +0000

A Different Approach to “Universal”

This amplifier started out with a stroll through a woodworking store in Oklahoma City, OK. What caught my eye was a single plank of a species of wood with which I’d never worked, “Marblewood” or zygia racemosum. The wood was expensive so I bought a single piece six inches wide and four feet long. Thus was the “Marblewood” amp born.

Now that I had the wood, I needed an amp to wrap it around. At his time I had just finished the rewire of the Lacewood amp using the information I had from the 6V6 bias optimization study. While doing that project, I thought that I should really design an entirely new 6V6 SE design specifically targeted at someone doing their first major tube amp build. This seemed like the proper opportunity to give it a try.

What is Wrong With Tech Companies Today?

Thu, 08 Mar 2018 00:00:00 +0000

A little background. I am a thirty year Electrical Engineer. I have spent those thirty years woking on some of the most amazing pieces of technology ever built. I have worked with cutting edge technologies before most people knew they even existed. I have had a phenomenal career. And I’ve spent that entire career with one company. That company has treated me very well, and I am grateful. But times are changing.

Something New

Mon, 05 Feb 2018 00:00:00 +0000

So, CascadeTubes now has a Twitter feed. The link is “CaliSuncalc”. The link is also on the left side of the Blog page.

If you ask me what that means for the site, I can’t really say. There are a few tweets there already. This is going to be a journey of discovery. So I guess we’ll see how it goes.

Feel free to take a look or even follow my tweets.

Projects Coming Together

Sun, 04 Feb 2018 00:00:00 +0000

There is something very satisfying about seeing a project really start coming together. I finally got some time today to start working on my 6V6 Marblewood amplifier project. It now looks like an amplifier instead of just a pile of boxes and parts.

The 6336 SET Amp

Mon, 27 Nov 2017 00:00:00 +0000

Just An Idea

So for quite some time, actually since first designing a 300B amplifier back in 2010, I have been playing with the idea of designing a nice intermediate power (5 to 10 watt per channel) SET amplifier. But I didn’t want to revisit the 300B or 2A3 DHT power triodes, I wanted something different and something that didn’t have the obvious drawbacks of the DHT tubes.

Early Morning Lightning Storm

Tue, 21 Nov 2017 00:00:00 +0000

So, this morning, I got a little reminder about the nature of the technology we all use. I currently have the 6EM7 Vertical Amp in my office at home connected to my computer sound card. When I reached over and turned it on this morning I got an interesting surprise.

One Busy Summer

Mon, 04 Sep 2017 00:00:00 +0000

I imagine that some folks have been wondering where I’ve been since the end of May. The truth is it’s been a very busy summer. Shortly after my last blog post, I learned that I was being transferred for the second time in less than two years. So far this summer I’ve bought a new house, moved ≈1500 miles (≈2400 km), totally packed and unpacked an entire house, a complete workshop, and an electronics lab, started a new job, and basically just tried to keep my head above water. However, in the process of unpacking things at my new house, I found something interesting.

Something Different

Sun, 21 May 2017 00:00:00 +0000

A while back, I was at my local hardwood supplier and found a plank of wood of a species with which I was unfamiliar; marblewood (zygia racemosum). This is a South American hardwood with a golden yellow to orange color and large dark streaks of deep brown throughout. This, I thought, would make a very interesting chassis.

The 6V6 Lacewood Amp V2.0

Fri, 19 May 2017 00:00:00 +0000

Same Skin, Different Muscles

The 6V6 Lacewood amp was designed and built in the first half of 2011. At that time there were two important aspects to this build. The first was that it was partially an experiment to see if an alternating current filter supply would cause 60Hz hum in the output if the B+ supply was very clean. The second important aspect was that the UL power stage design was based on a pentode mode bias point pulled directly off the 6V6 data sheet. The amp turned out very well at it was my main listening amplifier in my office for several years.

One Little Transposition

Thu, 18 May 2017 00:00:00 +0000

Well, my blog seems to be quickly becoming a list of things to avoid doing. I’ll get back to the more technical stuff soon but in the mean time I have one more blooper to share. I hope there aren’t too many objections.

So I have a new amplifier I just finished which will soon be added to the ever growing list of amplifiers on the web page. But when I was putting it together I managed to destroy a couple of expensive tubes due to a very simple error early on in the design process. Let me explain.

The 6DJ8 Headphone Amp

Sun, 09 Apr 2017 00:00:00 +0000

Something A Little Different

I have never been fully satisfied with the designs of most vacuum tube headphone amplifiers. The reason for this is because so many of the typical designs have some serious shortcomings.

The typical cathode follower designs tend to be high distortion and sensitive to headphone impedance. The more exotic types, including the White cathode follower and the popular but misnamed SRPP, tend to be highly sensitive to component and tube variation. And both types of designs require large output capacitors that distort the sound and suffer high leakage currents; resulting in DC offsets which stress, and can even destroy, headphones. Most designs that use output transformers tend to be noisy and are required to be closely matched to the intended headphones. Hence, these designs tend to be only medium fidelity and lack versatility.

It's Supposed to be Fun!

Sat, 01 Apr 2017 00:00:00 +0000

Sometimes I feel like an idiot!

A Note on Feedback

Thu, 16 Mar 2017 00:00:00 +0000

This is a copy of a comment I made during a forum discussion on “improving” the response of an amplifier.

So lets talk feedback for a minute. There are lots of ways to apply feedback and all feedback performs the same function. Any differences in feedback response are usually due to the different impedance functions applied to the feedback loop. Contrary to popular opinion, there is no magic in any feedback function. The effects of feedback are to reduce gain, increase bandwidth, reduce circuit induced distortion and noise, and decrease gain function sensitivity to circuit parameter variation. And it works. We’ve been using feedback amplifiers widely since Harold Black introduced the concept back in 1934.

I'm Making a Request

Thu, 02 Feb 2017 00:00:00 +0000

When writing for a webpage or a blog it is sometimes very difficult to get a feel for your audience. You never really know if you’re talking to a few friends over coffee, standing in front of a classroom of twenty, or lecturing to an auditorium of two hundred. I know there are a few people with whom I regularly converse, but my web traffic suggests that there may be more. So in order to help me get a feel for all of you, I am proposing a CascadeTubes version of Groundhog Day. Allow me to explain.

A Lesson in Chassis Building

Fri, 20 Jan 2017 00:00:00 +0000

Everyone knows that you need to be careful when working with metal. Corners are sharp, shavings get everywhere, power tools can spin and throw pieces of metal; so it’s kind of obvious you need to be careful. But how about handling the other materials?

A Lesson in Power Stage Distortion

Sat, 14 Jan 2017 00:00:00 +0000

Lately I’ve been looking at a project that’s been sitting on the back burner for quite a while. It’s a stereo power amp for which the 6EM7 Vertical amp chassis was a proof of concept. This amp uses an 807 tetrode in a triode strapped configuration. Now the one thing that I didn’t care for in the load line design was the level of distortion. From the load line paper design, distortion peaked at around 8% at 4.31W output, yielding a Ds of 1.8%/W. This is larger than I generally like in my amps. Then I had an idea.

Low Frequency Output Transformer Performance

Sun, 01 Jan 2017 00:00:00 +0000

There are a lot of opinions out there considering what’s acceptable for low frequency amplifier performance. It seems like everyone has their own very strong opinion about how low the frequency response must go for an amp to be “acceptable”. And it seems that usually these opinions range from somewhere between 40Hz and 20Hz as the minimum acceptable “roll off” frequency with definitions of “roll off” ranging from “no loss”, to “-1dB”, to the Engineering standard of -3dB. And strangely enough, virtually no one ever addresses the technical performance of amplifiers at their low end rolloff frequency. Amplifier distortion is usually only measured (when mentioned at all) at 1kHz and not across the frequency band.

Why Cascaded Drivers?

Thu, 22 Dec 2016 00:00:00 +0000

Lately I’ve been looking into drive topologies for Single Ended Triode (SET) power stages. The major benefit of power triodes is of course how great they sound. The major down side, from the perspective of the amplifier designer, is the fact that their power sensitivity is very low. What this means is that it requires a large voltage swing to drive these tubes. Some examples from my recent designs: a 6AS7 SET design that requires ±75v, a 6336 SET that requires ±81v, and a triode strapped 807 “SET” that requires ±72v. All from a line level inputs of between 1v and 2v peak.

SET Driver Revisited

Mon, 19 Dec 2016 00:00:00 +0000

So I was looking over the prototype work I’d done for a 6336 Dual Triode SET amp driver stage. This is the unit that I discussed on the “Brassboard Prototypes” page. However, when examining the pictures and performance, I noticed that something wasn’t quite right. So I took apart the brassboard and took a look. Sure enough, I had built the unit slightly differently than what was in the written schematic on that page.

A Tale of Two Chokes

Sun, 01 May 2016 00:00:00 +0000

As part of my fascination with vacuum tubes I am almost constantly laying out different amplifier chassis designs. I usually have between two and four different designs in process at any given time. This generally follows a very predictable pattern: design the amplifier schematic, choose a size and layout which is pleasing to the eye, then try to cram everything into the resulting (usually too small) chassis. It seems I am nothing if not predictable.

Because of this personal failing I am usually looking for component choices which are as small as possible. Which brings me to the point of this post; power filter chokes. I have gotten to the point where I simply will not build a tube amp power supply without one. There is too much benefit to performance to not have a good choke in the main filter. There is only one problem, chokes tend to be big.

Triode Sound. As Good As It Gets!

Thu, 21 Apr 2016 00:00:00 +0000

Sometimes when you’ve been working on technical stuff and just listening to music in the background you can kind of forget why we do what we do. Then there are times like right now. I just reached deep down in my music collection and put on the original 1984 mix of Stevie Ray Vaughan’s “Couldn’t Stand the Weather”. Now I’m listening to 8 minutes of Stevie doing the Hendrix classic “Voodoo Chile (Slight Return)” through an all triode signal chain and I’ve got goose bumps it sounds so good.

Optimization of the 6V6 SE-UL

Wed, 20 Apr 2016 00:00:00 +0000

Introduction

One of the main problems encountered in modern vacuum tube design is a great lack of available information. A good example of this is the data available for power amplifier tubes. Often times all that is available is a data sheet, some simple design point information, and maybe some plate circuit characteristic curves if we’re lucky. If someone wants answers about using the tube at a different operating point than that referenced in the data sheet they’re pretty much out of luck. And it’s not like today, we can simply pick up the phone and call RCA or GE and start asking questions about vacuum tubes. We modern tube circuit designers are on our own.

Producing Our Own Designs

Wed, 20 Apr 2016 00:00:00 +0000

Recently I have been doing some experimentation with 6V6 power tubes. As I was looking over some old designs I realized that I really wasn’t designing the 6V6 power stages so much as picking values and hoping for the best. This led me to develop an entire set of operation data on operating the 6V6 in Single Ended Ultra Linear (SE-UL) mode. You can read the results here (/optimization-of-the-6v6-se-ul-amp/) or over on the DIYAudioProjects site (http://diyaudioprojects.com/Technical/6V6-SE-UL-Bias-Optimization/). But it also got me thinking more generally about a common problem we all share, a general lack of resources to support the vacuum tube circuit design process.

Sizing Up a New Power Triode

Sun, 03 Jan 2016 00:00:00 +0000

I’ve been working on a new SET amplifier design. It’s a modern (well at least more modern) approach to an all triode signal chain with a relatively high power output (about 7.5w into the output transformer). But there’s a catch, I’ve never personally used this power tube before and there really isn’t much information about it floating around the internet. You see, instead of going with some huge transmitter output tube like the 211 or an over hyped DHT like the 2A3 or the 300B, I took a different approach. I decided on a very linear, high power, pass triode; the 6336A.

Brassboard Prototypes

Tue, 22 Dec 2015 00:00:00 +0000

I would like to take a moment to talk a little about “brassboards”. Everyone in the DIY community knows about prototyping. This is the “tryout” phase where we wire things up to see if they’ll work before we start a build. Sometimes it’s just part of a circuit, sometimes the whole thing, but there is one thing that all these prototypes have in common. They are in no way representative of the final project. But what do we do if we need to take our “tryout” one step farther before we build our project? What if there is something different in our circuit we haven’t built before. What if something in this design doesn’t look “right”? What if the circuit looks ok but the physical wiring looks like it will be a challenge? This is where brassboards come into play.

The 6CY7 Amp

Sun, 14 Jun 2015 00:00:00 +0000

An Exercise in Reuse

This amplifier came about due to an unexpected turn of events. Those with sharp eyes will recognize that the chassis for this amp is actually from the “Recovery” headphone amplifier. This is what happened. Shortly after I finished the Recovery amp, I started work on my 6V6 Lacewood amplifier. I used the Recovery amp for a while, however when the 6V6 Lacewood amp was completed, it quickly became my default amplifier for most of my music listening. By this time I already had the “Rebuild” headphone amplifier for my desk at work and I had largely stopped listening with headphones at home. This meant that the Recovery amp was put aside.

The 6EM7 Vertical Amp

Mon, 08 Jun 2015 00:00:00 +0000

A Historic Turn of Events

A very interesting thing happened in the electronics industry during the middle of the 1970s. This was a time of great turmoil of which few people were aware. The mighty vacuum tube had been the mainstay of the electronics industry for over 65 years. It was the technology that had helped win World War II. It was the technology that had put men on the moon. It was the key technology which had brought ease, connivence, and comfort to millions of people. Virtually every element of industrialization and modernization had been built on the vacuum tube. It was also a doomed technology.

Dummy Speaker Load

Sun, 08 Feb 2015 00:00:00 +0000

A Proposition

Just because something is a piece of test equipment doesn’t necessarily mean that it has to look like a piece of test equipment. This proposition is where I started with this particular project. I have a couple of amp projects in progress and was thinking forward to testing as I was putting the chassis together. In the past I’ve just wired some power resistors across the output terminals for testing and called it good. But, as I looked at a piece of heavy aluminum plate stock sitting on my workbench, I decided that I could do better; and make it look better at the same time. Thus was this project born.

How Amp Technology Affects Volume and Power

Mon, 14 Apr 2014 00:00:00 +0000

I’d like to take a few minutes to talk about about required amplifier output power. People who advocate low power single ended (SE) amplifier designs often get a bad time about the low output power of their amps. Due to the nonstop marketing forces of the consumer audio equipment industry over the last 40 years, most people think that 25W to 50W per channel is the absolute minimum acceptable power for any “decent” audio amplifier. They have been told repeatedly that this type of power is required to get any volume out of your system. But is this really true? Most of the are SE tube amps are from one to four watts peak output power. This seems totally inadequate to the “well marketed” masses but in reality, it’s much more power than you’d think. Matched to appropriate speakers, in a normally sized room, these amps can put out a surprising volume level and very dynamic sound. So let’s investigate how this could be.

A Consequence of The Quest for 20Hz Roll Off

Sun, 09 Feb 2014 00:00:00 +0000

In my post on how much audio bandwidth was really required, I posited that there was not sufficient benefit to justify the impacts of pushing the low end frequency response of our tube amps down to 20Hz. As part of that post I included the following statement.

“In order to pass really low frequencies the primary inductance of the output transformer must be rather large. Now the difference in frequency between 20Hz and 40Hz is a full octave. This means that a transformer designed to pass 20Hz at the same level as one designed to pass 40Hz must have a primary inductance which is twice as large. This equates to a much larger and more expensive coil and also introduces complexities at the upper end due to interwinding capacitances. This drives one to rather expensive solutions.”

Functionality is Where You Find It

Tue, 28 Jan 2014 00:00:00 +0000

After you’ve been building audio gear for a while you begin to acquire all sorts of miscellaneous test equipment and I am no exception. So today I was looking at a couple of audio function generators that I use to test amps and preamps. One is a relatively modern Tenma 72-455 and the other an older vacuum tube unit; a Precision model E-310. Neither of these units have been calibrated in all the time that I’ve owned them except for some rough checks involving a speaker and a tuning fork. So today I began thinking about calibration.

How Much Audio Bandwidth?

Fri, 27 Dec 2013 00:00:00 +0000

There is an ongoing debate in audio circles about just how much frequency response is really required from an audio system. Different systems for different uses may have vastly different requirements. The audio response required for a media room amplifier where various sound effects, explosions, noises, as such must be accurately reproduced may be far different that that required for orchestral music or jazz listening in a study or living room. So the pertinent question becomes, “For what conditions do we design?”.

Why Tubes?

Sat, 14 Dec 2013 00:00:00 +0000

So I get the question all the time “Why tubes?”. I usually answer something along the lines of “I just like them” but that really doesn’t sum it up that well. So I have been thinking about that very question; “Why tubes?”. After much contemplation, I think I have come up with one simple answer that sums up my feelings on the topic quite succinctly:

Why tubes?

Because vacuum tubes are like MOSFETs, but with class!

The "Universal" Preamp

Tue, 17 Sep 2013 00:00:00 +0000

Humble Beginnings

The basis for this amp started out as a post in a thread on the DIY Audio Projects Forum site. One of the members had suggested building a Super Simple Single Stage Preamp (“4S” Preamp for short) and there was much discussion concerning various tubes, gain, noise, etc. and several designs were presented using various dual triode tubes. Then the proverbial gauntlet was thrown down with the phrase “switch from 12AU7 to 12AX7”. My answer was to design a universal stage that would work well with an entire range of tubes. Thus was the 4S “Universal” preamp born.

Carbon Vs. Metal

Tue, 03 Sep 2013 00:00:00 +0000

So whenever you go out to an audio equipment forum on the web, inevitability the topic of discussion will turn to resistors. This is especially true on vacuum tube audio forums. And the discussion always seems to come down to two entrenched camps; the Carbon Composition guys and the Metal Film guys. The Carbon Composition guys always claim that metal film resistors make equipment sound “sterile”, “dry”, or “cold”. The Metal Film guys counter with the fact that carbon composition resistors are noisy producing “hiss”, “pops”, “ticks”, or just “white noise”. And then the fight is on.

Volume Control

Sat, 24 Aug 2013 00:00:00 +0000

The Problem

Here’s the thing… When you are building different amps and preamps, you want to listen to different ones all the time. You end up switching different units in and out, reconnecting things, basically reconfiguring all the time. Invaraibly, at some point you are going to want a nice simple volume control to adjust a level. This is not necessarly as simple as it may sound. You need to consider impedances, grounding, type of attenuation, method of connection, ease of use, etc. So I decided that I needed to tackle this problem.

The 6AS5 µ-Power UL

Fri, 23 Aug 2013 00:00:00 +0000

A Micro-Power Powerhouse!

Here is a nice little amp that started out as an exercise in the inexpensive. The basis for this amp was a stack of 6AS5 power pentodes that I got for $2 each. This is a little power tube initially developed for automobile radios. As such, it’s not very powerful and runs off of fairly low B+ (150v max). Typical operation, at least on the data sheet, is 2.2w into the output transformer with 10% THD. I was determined to improve on this distortion performance even though I knew it would cost me some power. When ever possible I selected surplus components (or at least those I already had on hand).

On Prototyping