IMO: Some of the ST70's I have seen here are beautiful. But... They still have the same circuit as the original amp. I would prefer a new input board with all new tubes that are different from the vintage 7199. The 7199 was a good tube 40 years ago but beter circuits are available out there that simply sound better. The 6G8H add a whole new world of resolution as well as 12AX7's, EL86?, 6SN7's and more. Making the B+ stiffer, and improving the power supply and tube bias removing the old power transformers and putting in a new one that can handle the extra voltage, removing the quad capacitors and strengthening
My ST70 has been with me for over 10 years and I have had it tweaked many times to get it where it is today. I have a $2500 amp here also (VTL ST85) that is still not superior to the ST 70 in my system on my Spica TC60's. I bought the VTL amp to drive a larger pair of fullrange speakers. But I have not found a pair yet so the VTL may find itself on the market soon. I don't think the ST70 mods go far enough with the improvements that warranty spending $700 plus. Trust me the circuits have not changed in the past 50 years so don't believe the hoopla!
I would have to go with the Primaluna Prologue amp because it has built in all the improvements like adaptive bias, a very good circuit for the input and of course your choice of output tubeslike EL34's or 6550's, and more. You will have more versatility and you will be able to hear the different flavors of each tube it can work with. You can't do that with the ST 70. And trust me I love mine and I haven't heard many amps up even up to that $5000 mark that blows it away. But if I were to look for a new amp today I would be looking at the Primaluna for sure.
My ST70 has been with me for over 10 years and I have had it tweaked many times to get it where it is today. I have a $2500 amp here also (VTL ST85) that is still not superior to the ST 70 in my system on my Spica TC60's. I bought the VTL amp to drive a larger pair of fullrange speakers. But I have not found a pair yet so the VTL may find itself on the market soon. I don't think the ST70 mods go far enough with the improvements that warranty spending $700 plus. Trust me the circuits have not changed in the past 50 years so don't believe the hoopla!
I would have to go with the Primaluna Prologue amp because it has built in all the improvements like adaptive bias, a very good circuit for the input and of course your choice of output tubeslike EL34's or 6550's, and more. You will have more versatility and you will be able to hear the different flavors of each tube it can work with. You can't do that with the ST 70. And trust me I love mine and I haven't heard many amps up even up to that $5000 mark that blows it away. But if I were to look for a new amp today I would be looking at the Primaluna for sure.