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Thanks to the awesome people on this forum and others I was able to unravel some of the mystery surrounding my Catskin SET amp. It will be some time before I really understand how it works, if I ever do. In the interim I'm building a system around it and looking into how to support it for the long term.
My question is about the importance of tube matching between left and right channels in SET output applications. Intuitively I can see the importance in a push-pull driver, but L-R? The Catskin amp designer's shop had all of the instruments necessary for matching all important characteristics of tubes, but when I grabbed the spare tubes for the amplifier, there weren't very many. As in, not enough of a sample to easily find a match. I've gone through the exercise of matching transistors and that can take dozens to hundreds to find a pair that is close. I assume that there is similar difficulty with tubes.
The Catskin amp has bias and flux measurement outputs via a DIN connector on the rear of the case. Is this all that is required to balance left and right?
Follow Ups:
Hi What's!
First, I couldn't find one single thing about a Catskin SET amp on the internet! Could you provide a link so I could check it out? Also what speakers are you using or planning on using with it?
Second, I've been using a Mastersound Reference 845, SET amp for 20+ years now. It uses four 845 tubes so it's actually a parallel, SET amp. Now just to be completely honest I'm not technically proficient. That being said, my amp allows for individual/separate bias adjustments for the L/R output tubes, as Rocket suggested, but I still always start with matched pairs for the front and rear --- see the photo of my amp up above --- or better yet a matched quad when I can get them.
I started in audio in 1964 at age 10, after I heard The Beatles on Ed Sullivan. But I didn't hear my first SET amp until 1999 when I was 45! The sound was so alluring and so correct, I sold all my audio gear and purchased that 135 LB, 40W/ch, Italian, Mastersound SET amp in 2000 and I've never once looked back or thought about selling it for a different type of amp! So good luck in your SET adventure.
Thetubeguy1954 (Tom)
Central Florida Audio Society -- SETriodes Group -- Space Coast Audio Society
Full-range/Wide-range Drivers --- Front & Back-Loaded Horns --- High Sensitivity Speakers
Hi Tubeguy,That is one gorgeous amp!
After some research of my own and help from nice people around the interwebz I am now in a position to tell you a little about the Catskin amplifier. You will probably have the same difficulty finding info on it that I did because it is a one-of-a-kind, or was. I'm not sure if anyone else has built one from the schematic and project description provided. The project is documented here. https://audiokarma.org/forums/index.php?threads/catskin-class-a2-set-with-secondary-flux-cancellation.780706/
The design is experimental in that it attempts, successfully I think, to use very inexpensive tubes and transformers to achieve performance comparable to very expensive amplifiers.
On recommendation from a helpful member in the SET forum I bought a pair of used Tekton Lore Reference loudspeakers. I don't have a hi-res audio source nor a good location to place the budding system, so I don't really know it's capabilities yet. So far I have a couple of hours on it and I like it/them. The mids are rich, full, and warm, as I would expect from a tube amp. The highs seem to be limited by the resolution of the source, but are still very crisp and clear. Lows are solid and punchy, but the limited dynamic range of the amp and speaker are noticeable. Over-all, the clarity is as good as I have ever heard from mp3 or CD.
There is something special about listening to an orchestra or small ensemble and being able to place the individual instruments in an imagined studio or concert hall. This system will never be good enough that I could pick out all of the instruments, but I can identify some.
You started in '64? That would be right about the time that the Catskin amp designer got his start; also as a child. His family was too poor to buy him electronic parts of any kind. So they placed ads on the boards of local supermarkets to take broken TVs. As a child, he taught himself the art of electronics with scrounged vacuum tubes. By the time he died his mastery was so complete that it was not a worthwhile challenge to design high-end amplifiers. He added extra requirements like the need to use very low-end, undesirable components.
Edits: 09/29/21
Hello, Again Whats!
First, allow me to thank you for the compliment about my Mastersound amp.
I checked out the link you provided and your CatSkin SET is quite the SET amp, my friend! The person who built it produced one of the nicest and neatest layouts of wires and components I've ever seen in any DIY, point-to-point, hand-wired amp in my life. You should feel proud to own such a well-built SET amp. IMHO just a little bit of wood would really dress that awesome little SET up quite a bit. I take it the red button on the front is the on/off switch? If so I'd place a piece of dark wood on the two sides and a nice piece of lighter wood on the front --- I'd leave the back as-is -- and I'd also use the same dark color of wood on the bottom as well.
Heck, What's, you could make it really simple and have it so your metal, CatSkin, SET, amp slides into a wooden box-like structure that's exactly as I described color-wise -- unless of course there's another color pattern you'd prefer -- it would be so simple because there's no wood on the back of the CatSkin amp anyway, so you could take the amp and slide it front-first by placing it on the bottom wood piece and then slowly pushing it forward until the red on/off switch or power on light, slides through the hole in the front lighter piece of wood.
The wood would not only make for a very nice-looking SET amp, but since the wood is not actually to any of the CatSkin's metal, it would remain easy to make repairs "if" required. In any event, whether you choose to keep the all-metal Spartan look, or should you prefer to make it a little more home-friendly or even give it more wife/girlfriend appeal is a choice you'll have to make for yourself. I'm an earth-tone guy who likes the look of wood, plants, and earth-tone colors in my home! So I'd have to go for the wood look.
Whatever you decide in the end, let me know, ok? Like I said. there are no rights or wrongs, I'm just curious what you'll decide to do. Heck, you can even send me a private message if you so choose. One last thing if I read correctly your amp is only 5W? If so you'll need to be pretty selective in the speakers you'll choose to use! In any event, best of luck in your continued SET journey What's...
Thetubeguy1954 (Tom)
Central Florida Audio Society -- SETriodes Group -- Space Coast Audio Society
Full-range/Wide-range Drivers --- Front & Back-Loaded Horns --- High Sensitivity Speakers
Hi TubeGuy,Thanks for your kindness and suggestions. I do feel quite proud to own that amp. *edit* I made a request to the widow to get the other amps designed by the same guy. I'm hoping... *End edit* I'm not sure what I'll ultimately do with it. At the moment it sounds great, but it gets really hot. I think this is one of the potential issues that the designer was referring to when he said "... but it's more complex than most SET amps in this power class and it lacks refinements that could improve reliability as well as temperature stability. At this juncture, CatSkin is more like an advanced experiment or early prototype than a production-ready design."
So if I want to use it very much I'm going to need to do something to improve cooling. Unless the caps are automotive temp range, and I don't think that hi-fi audio caps typically are, they're going to cook. Fortunately, electronics cooling is a big part of what I do for a living. Time is another matter.
At the moment I'm inclined to leave the amp unmodified. It is finished and complete as-is, even if not perfect. It is representative of a person whom I sorely miss. Any additions would be as you describe, external and removable.
As for a wooden shell, I'm with you on natural materials. The humble character of the Catskin amp has it's own charm, but I do prefer the look of those that incorporate fine woods and polished metals. I like tube back-lighting as well. I suppose aluminum is a natural material in a way, but you'll never see it in a pure form in nature. So to me it feels kinda artificial.
I did get some Tekton Lore Reference loudspeakers for the amp. There is a big disaster of a discussion about that over in the High Efficiency Speakers Asylum. I posted a photo of the budding system there. In it you can clearly discern my preferences for decor.
All the best!
Edits: 10/02/21
What's, you need to check into the ultra-quiet types of cooling fans made for computers. They're wonderful for audio use and I've included a link down below for the type I'd use, two of the 12v, 140mm high-speed units!
Thetubeguy1954 (Tom)
Central Florida Audio Society -- SETriodes Group -- Space Coast Audio Society
Full-range/Wide-range Drivers --- Front & Back-Loaded Horns --- High Sensitivity Speakers
Craftsman style was always into copper ...
Tube matching from one channel to the other is not necessary in a SET amp. But, I would use tubes that test within 10% of one another.
If you amp have individual/separate bias adjustments for the L/R output tubes, having the tubes matched is not needed.
Thanks! I'll have to learn how to perform the adjustments. I just found the original test jig that was used for setting those adjustments in development.
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