Lookin for an ST-70-like project

[taj]

Hi, I've been searching through here looking for a suitable project, but it's a difficult thing to search for, as I discovered. I've been reading random threads here that looked promising only to emerge hours later empty handed. But I've enjoyed what I've read so far, so it wasn't wasted time, and I'm in no hurry...

So I need your help and advice: I would like to build a tube amp that is pretty much everything an ST-70 is I suppose. Push pull, stereo, 30-50 WPC, commonly available (and reasonably priced) parts, well respected sound, lots of expertise and experience floating around, etc., etc. Definitely nothing exotic. And I'd build an actual ST-70 if only I could find a well-documented project that tells me which parts (and vendors) to avoid, what to watch out for, how to lay it out, yada yada. (Someone to hold my virtual hand).

I've been building SS amps for years and am beginning to understand their operation, so I want to learn the same way with at least one tube amp, and see how it goes from there. I'd like to build it from scratch, I'm not a kit buyer/builder -- no fun there. But I know very little about tube amp specific parts like the transformers, tubes, chassis, hole punches, etc., and must rely completely on a well documented project. Otherwise I'll screw it up by buying crappy parts for too much money, or laying it out so that it hums, burns and attracts mosquitoes.

Any advice, directions, referrals?

Alternatively, I could just "go for it" and ask a zillion questions here. Does that sound like a more reasonable approach?

..Todd

[planet10]

For the last month i've been listening to Gregg-the-Geek's DynaMutt.

I gave him 2 ST70 donors and got DynaMutt back. A step up from what i had before.

Gregg has circiut boards

dave

[taj]

Yeah I saw that. Gregg has some nice stuff there. Looks well done. And a convenient drivable location to boot.

But it's easy to stuff and mount a board (famous last words). Gregg's done all the hard work there. It's the other stuff that has me more stymied; transformers in particular. What are (in anyone's opinion) the best bang for the buck in power and output transformer options? ...Kind of a good/better/best ranking. I only know of the Hammond and Edcor brands. How do they compare? What other brands should I know about for an ST-70?


er... where'd you find all the surplus ST-70's, Dave? Is there a pawn shop nearby that specializes in them? Got 2 more to give me? I'll give you something back in return. (glancing around... really old cell phone, box of obsolete computer parts, ornery spouse...) Well, I can always hope.

..Todd

[Geek]

Hi,

You can get iron equivalents from Triode Electronics or Dynakit Parts.

Edcor's closest combo is XPWR002 (the 6.3V windings would **just** make the grade) and 2 x CXPP60-MS-4.2K

If I were building an ST-70 from scratch, I would use the Triode Electronics power transformer and the Edcor CXPP60-MS-4.2K OPT's.

er... where'd you find all the surplus ST-70's? Is there a pawn shop nearby that specializes in them? Got 2 more to give me? I'll give you something back in return. (glancing around... old cell phone, box of computer parts, ornery spouse...) Well, I can always hope.

Well, I had to beg one from Dave to work on... they still go for $$$ even completely kaput

Cheers!

[planet10]

A step up from the Edcor iron would be some of Bud's (O'Netics) entry level. He also has some power transformers that might be suitable.

dave

[SY]

I'm very curious to try the O-Netics myself. I've also been happy with the Dynaclone iron from Triode and ecstatic with transformers from James. The latter will take a bit of work to procure, but they're worth it- performance is excellent, pricing (including shipping and duty- DON'T use the air freight option!) is not outrageous, and they're beautiful.

[boywonder]

There is loads of ST-70 info over here, including boards, kits, etc:

diytube.com :: View Forum - st70

[taj]

The Triode ones are easy to buy. That's a positive compared to the others.

The James transformers (and chassis) look interesting. I have family in Taipei, so I'll to check further into those. Maybe I'll go visit this year, with an ulterior motive.

I cannot find any official information about O'Netics. Just lots of kudos and whatnot. Does he do strictly OEM sales, or does he have dealers, or sell privately, or is he just a very vivid figment of everyone's imagination?

..Todd

[SY]

Very vivid figment. BudP on this forum. Drop him a PM and I'm sure he'd be delighted to help.

[Evenharmonics]

Originally Posted by taj

I would like to build a tube amp that is pretty much everything an ST-70 is I suppose.

Is it the sound quality (via ultra linear P-P) of original ST-70 that interests you or is it the looks, price or is it something else?

If it's the sound, I can't think of a better option than to build the exact thing. Dynakit has the original design with newer parts. What I've done was to get a used ST-70 (mine was beat up) cheap, take it apart, then restore it with replacement parts here and there. I've learned a lot about this amp during that process. Dynaco Doctor was a big help.