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Old 10th September 2009, 06:44 AM   #11
rknize is offline rknize  United States
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For what it's worth, here is my Thomas Amp (originally pulled from a Thomas organ). It sounds decent for what it is and the design is quite simple. It was my first real tube project, so I went a little overboard when rebuilding it. Its main shortcoming is probably the output iron, or lack thereof. It also uses the "dreaded" 12AU7 in the phase splitter, which frankly doesn't matter much given that it has no gain. I've been meaning play around with the operating points a bit, but never got around to it.

http://www.knizefamily.net/russ/elec...-audio/thomas/
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Old 10th September 2009, 01:40 PM   #12
Cassiel is offline Cassiel  Libya
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Thanks Palustris, i had thought about that but never seen it so i was in doubt.
Anyway i still don't understand the 100 uF cap, bypassing all that loop.
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Old 25th September 2009, 08:51 PM   #13
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That's your cathode bypass cap.
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Old 26th September 2009, 02:52 AM   #14
athos56 is offline athos56  United States
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Quote:
Originally Posted by ChrisA View Post
I'm looking too. Here is random rambling about what I've found.......

I'm looking for a simple 6L6 based amp. I've not yet decided exactly what I want to build yet. But the outline is like what you want: 6L6 PP power section switchable between a couple modes, ultra linear and triode. It will have a "long tailed" phase splitter made with a 12AU6 (like the paraphase in the post above) some adjustable NFB and likely a gain stage ahead of that of that with 1/2 of an 12a?7. I prefer to build on a "turret board" (see here for an example: http://www.turretboards.com/images/P...ing_loaded.jpg) and here for more info: http://en.wikipedia.org/wiki/Turret_board. I think this style of construction allows for the best reliability, serviceability and allows for future "tweeks". PCBs are very hard to service or repair and point to point amps are hard to figure out as they tend to look a bit like a rats nest of parts.

I figure there must be some classic designs that "everyone" knows about. No I'm not trying to hijack the thread, 6V6 and 6L6 are so close. In fact if you think you want an 6V6 amp, find a 6L6 amp and build that but set the bias down for the lower powered 6v6 tubes, then you have to option at a later date to re-tube the amp for more power (assumming the transformers are sized for the task.)

If you want an easy to build modern design look at Tubelab. Find the thread on this site for the "simple PP" (simple push-pull) that will be available "real soon". Or you can build is "Simple Single Ended" design that is currently available and well tested. These amps use printed circuit boards so they should go together quickly. The simple PP and SE are flexible enough to use any of several difference power tubes from "big" down to 6v6. The site is here
http://www.tubelab.com/ But it is not yet updated for the Simple PP

I'd prefer not to build on a PCB. and I'm still looking for "clasic" 6L6 designs that I can study. I'm familiar with several 6L6 based guitar amps. So far I'm not seeing a lot of difference between 1950's guitar and 50's hifi designs except that the guitar amps will have a high gain preamp section. I'm looking for hifi designs from the same era.
A good place to find guitar amp schematics, many of which use 6l6 or 6v6 is here:
http://www.schematicheaven.com/index_HTML.htm
(hint, start with the Fender "bassman" if you want PP or a "champ" for SE. Both are very simple, to simple really for hifi. but educational.)

Look at Peter Millet's site. He has many scans of 50 year old books, several of them aimed at 1950's DIY HiFiers More than a few "how to build a xxx" books and articles there, all published 50+ years ago (so that the copyrights have expired)
http://www.pmillett.com/technical_books_online.htm
Thanks for the links, I remember seeing those books on Peter's site but had since forgotten they existed.
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