Blogs

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 I did that! How could I have been so thick headed to make this kind of mistake?

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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?

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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 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.

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 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.

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.

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.

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

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.

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

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.

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.

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.

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

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.

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.