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.
When I first started working on the 6336 SET I was looking for an answer to the very low sensitivity of the big power triodes. My solution for that amp was the cascaded driver documented here and here. Well, that solution worked out so well in the 6336 SET that I decided to use it in my new amp as well. And this is where the trouble started.
I settled on the 6AS7/6080 as the power tube for the new amp. This is a dual triode pass tube like the 6336 but it is a much simpler tube with which to work. The power levels in the filament and plate dissipations are not nearly so extreme so it runs significantly cooler. It also doesn’t require the kind of warmup time that the 6336 does. And best of all, it has the same pinout as the 6336.
So at first I decided to simply use the same basic layout for the amplifier top plate as the 6336 amp. I took the same 12 1/2″ by 9 1/2″ layout used for the 6336 and modified it for different transformers and choke. And at first I was happy with my design. But there were a few issues with the wiring layout that I had not worked out. So I put it aside for a while.
When I came back to it after a couple of weeks, I had a mental shift and decided that what I really needed was a more simple layout like the Marblewood. So I spent yesterday coming up with an entirely new layout based on the more open Marblewood design with the primary filter choke below the plate. And when I finished the internal layout and worked out all the problems, I didn’t like it.
And now I’m at an impasse. I have two separate layouts for this new amp, with neither am I particularly happy, and I need to decide how to get myself out of this particular dilemma. I have an idea on which way to go based on the iron I already have on hand, but I’m not completely sure yet.
So what do other people do when they run into this kind of design impasse? I had to order a couple of 2.5kΩ output transformers from Edcor for the new design, so I have about six weeks to come up with a layout solution and choose some hardwood for a chassis.
I’m interested in what other people have to say. Any suggestions on what path I should take? And why?
Not knowing how to set out a tube amp for my first attempt I had a look around the various forums for ideas. This site was interesting for different layouts but not that different to some of your designs. http://single-ended.com/
In the end I went with a commercial pcb initially and later converted to point to point. How to get a pleasing top and underneath layout is certainly difficult. I have all the small parts to build this 6as7 amp based on the preamp and driver stage of the Beast amp which had the two small chokes so I will be following with interest for changes to the circuit I should consider.
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Personally I don’t like the look of your 6336 SET, it looks heavy/congested. However tube amps have a lot of iron and there’s no escaping it. I like the look of the Marblewood better, it looks cleaner, lighter. But even the Lacewood with all the Iron on top looks better to me than the 6336. So IMHO if you put most of the iron on top spread it out, I think that looks better than all scrunched together; and, I personally don’t have a problem making the chassis bigger no matter which way you go. Also I’ve often wondered why the chassis on an amp needs to be rectangular, nostalgia? Certainly it simplifies construction, but thinking outside the box might give you some ideas. Perhaps look at what others have done and see if anything strikes your fancy. I’m very interested in what you come up with.
Hmmm… I hadn’t thought about a spread out design more like the Lacewood. The Lacewood top plate is 11″ by 14″. This is significantly larger than the 9-1/2″ by 12-1/2″ I was working with; about 30% larger. Maybe I’ll think bigger.
Some sketches of the proposed layouts for review would be helpful.
My personal designs (mostly solid state stuff) usually follow the most logical signal path, while keeping as far away from 120V wiring, power transformers, etc. All of my completed designs are housed in enclosures, so aesthetics are not important like they would be in an open chassis tube design. I would think the layout that produces the most symmetrical topside layout might be best for what you are building. Over the years I have repaired many tube type radios and audio equipment, and commercial producers have no regard for the fact that under the chassis is a veritable rat’s nest of wiring and components.
So, I would say, produce the most pleasing topside layout, and make the under chassis stuff as best you can for the layout.
In reality this is mostly about esthetics and ease of assembly. Looking back on other projects, it just seems that every time I put the main filter choke under the hood, the final wiring is more difficult. I may stick with my original thought of using the layout from the 6336. It has the same top plate size and all the transformers and chokes are smaller so it shouldn’t feel as visually “heavy” as the 6336 amp. And it will definitely be much cooler running.
I wonder what people think is about the biggest physically a stereo tube amp should reasonably be.
If the main filter choke has end bells and a nice paint job, it can live topside. An open frame choke probably needs to live “downstairs”.
As far as size, it needs to fit where it will “live”, and not be so large and heavy thar it needs special support or is difficult to pick up and carry around. How big is a tough question to answer off the cuff.
One other possible aesthetic “improvement” might be to lose the “Edcor blue” and maybe paint the iron gloss black. Looks more “stately”.