How good is Dynaco ST70 pwramp?

Great description David. The only thing I might add is that Sound Valves produced the Dyna 70 when it made it's comeback a few years ago (short lived).

The current Sound Valves (brand) are almost the same amp and was originally very reasonably priced. There were both mono and stereo versions, and available as a kit or fully factory assembled. I bought two of the factory assembled Stereo 70 versions for my surround system about six years ago and have had zero problems.

Thank you Albert.I might add,these amps are easy and fun to work on.I hard wired a heavy gauge power cord on mine which I swear made it play louder and improved the bass quite a bit.I believe they sold for around $600 back in the 60's and hold their value fairly well.As I said,mine cost $150 but usually they go higher depending on condition,mods,tubes etc.A sweet and fun amp!

There are several mod's out there that increase the performance of the amplifier. Van Alstine has one that basically includes an entire new circuit design and board. Only the tubes, power transformer, and chassis are kept. The Soundvalves one mentioned in the second post is another. I don't know if it isn't so much a mod as it is just replacing the older parts with modern, presumably better, ones, but leaving the original design largely untouched. They do address some of the weaknesses of the earlier design. If I recall there may be one or two more companies out there that offer some type of improvement to the original design. The Van Alstine improvements are more of a major overhaul to the amplifier. I would add that I'm usually not to fond of modifications, but with this amp, any of the ones available are probably ok, especially given some of the older ones may need part replacement anyhow. $350 seems to be the price I've seen most often on the net. avahifi.com and soundvalves.com