Will Vincent. 208-746-9650
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It depends on what you're looking for from the amp. If you want to preserve its original circuitry and tone, I'd say Will Vincent does a nice restoration of the original with a few small upgrades; for a bit more modification of the circuit the Curcio has had many nice things said about it. If you want to radically overhaul the amp, get Kevin Carter's ST-70 upgrade kit from K&K Audio. It utilizes the chassis and the output transformers from the original, but upgrades the entire circuit board, power supply and power transformer, and gives you a lot of flexibility in output tube choices right up to a KT120.
Ever thought about doing it yourself? I had a stock ST-70 that I completely rebuilt using Curcio boards. I had a blast and it turned out great.....basically replaced everything but transformers. New caps, new driver board, new RCA jacks. If you were interested I would rebuild yours for next to nothing but the parts.
Andy, great thread. Don't intend to hijack, however feel another thread on this would just confuse.
Stuart, What was the cost of your project? I have a ST-70 that has been stored since the 60s. In great shape but needs new capacitors etc due to age. I am considering doing this myself however have not looked into it at depth.
Mesch, if you just want to get the amp up and running, you have to fix the power supplies. The 525V main filter can is available from Antique Radio Supply in Arizona. You will also want to replace the bias power supply caps and the attendant rectifier (the original is a selenium; selenium rectifiers should be replaced when and wherever they are encountered).
If you do those things correctly its likely that the amp will run fine if the tubes are OK and it was otherwise operational when stored.