6l6-Se-Ul

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.

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.

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.

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.

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”.

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’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.

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

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.