6l6

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.

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.

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

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

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.

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.

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

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.

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 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.

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.

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

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.

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.