Stereo Audio Amp building resources?

[FiddlinJim]

Hey amp-building buddies,

Let's say you've built a few cool tube amps for guitars you're looking at your crappy stereo system and thinking: "Hmmm, wonder if I can build a stereo tube amp with a few selectable inputs for my iPod, a CD, etc...".

Where would such a fool start looking for schematics for stereo amplifiers that might be similar to 50's Fenders in terms of complexity and component availability? Anybody know of a decent starting place on the Web to start researching existing designs?

[celeste]

For just schematics, try http://www.freeinfosociety.com/elect...page.php?cat=1

[muchxs]

Why not just buy one on FleaBay? There are a ton of cool old integrated amps out there just waiting for you to bring them home. Look for H.H. Scott, Fischer, Stromberg-Carlson... even old Magnavox amps are pretty cool.

Old tube hi-fi amps are like guitar amps with better transformers. You're going to want a big power transformer because stereo means twice as much of everything. You could go single ended 6BQ5 on the low end or 6V6 and 7408 Williamson circuits in the medium price range.

High powered hi-fi usually means monoblocks, each side of the stereo pair has its own power supply. Look at old Heathkit, Dynaco, maybe McIntosh if you can afford them. Heathkit A-7s are great amps for reasonable money.

The RCA RC30 tube manual (available as a reprint) has some hi-fi amp circuits in the back. There's a 15 watt 6973 amp, a 30 watt 7868 amp and a 50 watt 7027 amp. If you really want to go crazy there's a tube AM tuner circuit, a tube FM tuner circuit, a superhet convertor and a Baxendal stack tone control circuit in there. All cool stuff!

You could Google tube hi-fi and start sorting through the nearly 7 million links...

[mojo2001]

I would say scratch build and use recycled transformers....although I have also had real good results with cheap Hammonds and the like.

The problem with using commercial designs is that many of them are more complex than they have to be which can get you into trouble as a novice.

I'd suggest looking over some old 1950s EICO power amp schematics. Relatively simple, solidly engineered designs. Give you an idea what you're looking at.

The major thrust in DIY audio is building simple, low powered amplifiers, which is great if you have speakers that can run off of a few watts. It is almost worth getting the right speakers if you're looking to get into building.

[markw51]

Look at a couple of the projects under the How To Section at:

www.angela.com.

These are for SE amps - single ended vacuum tube amps - kinda like a Champ 600 but for hifi.

They are simple to build since there is a low parts count and sound fabulous. But they are not high power so you'll need to pay attention to the sensitivity of your speakers.

[eugenedunn]

Hey, you might try to buy a used Dynaco Stereo 70 (ST-70), then recap and possibly mod it some of the cool mods out there.... like those from Wellborne Labs, etc.....

Those run EL34's, 5AR4's and a couple of hard to find driver preamp tubes, but many of the mods out there do conversions to easier to find preamp tubes.

The Dynaco Stereo 70 was one of the most abundantly produced kit form Hi-Fi tube amps back in the 60's. Check them out, you might find one cheap.

I have one myself that I've been planning to recap and service..... too many irons in the fire at the moment though.

[FiddlinJim]

Thanks folks... That's a great start for me. I'm more interested in a build from scratch than a buy; the goal is to DIY and learn, learn, learn. Low power is what I'm looking for, for sure.

I do have an old Silvertone stereo a friend gave me that I can restore.

Thanks for all of the suggestions!

Jim