Refurbish a Dynaco St70

To rebuild a Dyna ST-70 is not that nuts! We do it all the time. The filter caps are readily available as the amp is so popular and the tubes are easy to find too, although the 7199s have been going up in price recently.

A properly-working ST-70 is actually a respectable amplifier. They have distortion figures that gave their competition conniptions back in the day (Hafler was an excellent designer) and so rival much more revered amps like the Marantz 7B.

There is an excellent thread about the ST-70 on audiokarma: [ur]http://www.audiokarma.org/forums/showthread.php?t=578485[/url]

Depending on how in-depth you'd like to go; Joe Curcio may be the best person to contact. He has decades of experience, in rebuilding/modding the ST-70. These amps have some excellent transformers, which are(arguably) the most important components, of a tube amp. The only major problem, with owning a completely stock ST-70, is finding a source of NOS or high grade 7199 tubes(my favorite was the Sylvania). They're almost extinct(Unobtainium) and there is no direct/plug-in replacement. It's not too hard to rewire the tube socket, to receive the pin configuration of the 6GH8A tube and adapters are also available. NOTE: When I say, "completely stock," I'm not saying one with the original caps and resistors, which absolutely should be replaced, to obtain the best sound and any kind of reliability. The only part that can be hard to find(for a stock rebuild), is the quad-cap. There's a seller on eBay(http://www.ebay.com/itm/NEW-30-20-20-20-550V-ELECTROLYTIC-CAPACITOR-DYNACO-DYNAKIT-MKIII-MKII-ST-70-/331196180628) and Curcio Audio also offers a kit/upgrade for it: (http://curcioaudio.com/dynadr_3.htm) I used to buy mine from Antique Electronics Supply, in Tempe, AR. Replacing the inputs, outputs and power cord, without chopping up the chassis, is pretty much a cakewalk. Have fun!

Personally- if I were going to rebuild an ST-70 now days and retaining a MOSTLY stock(tube rectifier/greater filter cap capacity) power supply(like I used to), I'd use this board: (http://www.curcioaudio.com/st7upg_3.htm), stuffed with higher quality components. I just happen to love the Siemens CCa and this board would make it's use possible.

Definitely waste your time on refurbishing. As point of comparison look at the Van Alstine update.

Thanks much! The responses are exactly in the form I was hoping for.

Atmosphere, am I correct in thinking that you (your company) rebuilds them for others that supply the amp?