About a month ago, I found to my utter surprise an original ST-70 box inside of which sat an un-built ST-70 kit complete except for one of the output transformers that was missing. I then vaguely remembered that, on testing a unit that I had just finished building, one of its output transformers had shorted and I had replaced it by taking one from an un-built kit box. Obviously, this was the kit I had taken the transformer from. What a strange experience to see again the transformers in padded paper material, the cardboard-wrapped output tubes, the chassis! I was back in the sixties! A bit like a time warp indeed!
So, I decided to built the kit and I started looking around on the Web World to find resources and information. I was somewhat shocked to witness the legend that has been built around this amplifier and the sheer availability of parts and modification kits.
So much so that after a while, I became confused about what to do.
- • Should I try to get an original output transformer to complement the one I have or go for the new ones being offered ? I have just found an old ST70 in horrible shape (very dirty, tubes missing and driver board broken) but the owner offers to sell me one of its output transformers. Will it match the one I have? I suppose that throughout the life of the ST-70 there were different output transformers; how can I recognize if the one being offered is the same?
• Can I use the electrolytic capacitors after all those years ?
• The PC board is the original phenolic type; is it better to buy an identical but modern one or to acquire the new board their different drivers? Opinions here seem widely divergent.
• I notice that the output tubes (the four of them) have the number "3" written on top of each one. Anybody knows what it is for?
• Apart from the electrolytics, should any other discrete components, such as resistors, tube sockets, etc. be replaced?
I am relieved to have found this forum! I would very much appreciate receiving some guidance as to how to proceed to put together this piece of equipment and have it sound even better than the original.