How good is Dynaco ST70 pwramp?

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

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!

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.

The Dynaco ST-70 is a classic amp from way back.It was a Stereophile rated class B in 1966.The first ones are as old as 40 or more years.The pre 1969 ST-70's are considered the best as the transformers were made by Dynaco and are considered very good even by todays standards.In 1969 Dynaco started using Japanese made transformers that many feel degraded the sound quality.There are many mods. for the Dynas and good NOS tubes really make these amps sound sweet.David Hafler designed the ST-70 which is rated at 35wpc.It is said 35wpc is not the true specs.for this amp and its more like 25-30 wpc.I had a Jolida 502A (60wpc) which I sold d/t personal reasons.The 502A sold for approx.$1000 new.After I sold the 502A I found a ST-70 for sale in the local paper for $150.It came with Sylvania EL-34's and Sylvania 7199's.My first impression was, although not as powerful as the Jolida,the ST-70 sounded as good in many ways.I have since sold the ST-70 ($450) and replaced it with a Pass Aleph-3 The Pass is better sounding in all areas and throws a much larger sound stage.Even though,many nights listening to music I still think of my old beloved Dyna.There was a real magic to her.