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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.

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.

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.

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.

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

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.

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”.

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!

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.

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.

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.

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.

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.

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!

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’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.

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.

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.

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!

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.

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.

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

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.

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.

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

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.

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.

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.

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

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.

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.

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.

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.

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.

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

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.