• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Modded ST70 Done

Here's my take on a ST70:



And some quick guts shots:



DIYTube Driver Board
Edcor 4.2k Outputs
PA-060S Power Tranny
SDS Cap Board
Dual Hammond 159v Chokes (Run in Series - needed the current rating)
Winged 'C' KT88's
RCA 12BH7s
Phillips 5751
Triode Mode Switch
Tiger Maple Base finished with water based dye and button shellac

Just a note on the Edcor's - They are 180' out of phase of the old Dynacos, you will oscillate if hooked up like the old dynaco's were :nono:
I just have it breaking in right now; so I won't comment on sound. It really does sound sweeeeeet though :D

Are you sure your problem wasn't because your red and yellow wires need to be swapped? If hooked up correctly you wouldn't have had to be 180 off on the transformers.

Your using a switch to switch to triode mode? I thought that was a big no no because that switch is only rated to 250 volts.

What are the output transformers rated for in output? Looks like the big replacement power transformer too.

In all a nice job!!! Love the wood chassis too.:)
The board itself is out of phase; so 'usually' you need to criss-cross like that. I in fact needed to go back and uncross them.
Triode mode switches rated for 330vac will be fine - just ALWAYS only do it once the amp is off.
The OPT's are rated for 60w, and the PT is the Triode electronics replacement (good for 300mA I believe).
On the driver board - I did go back and shrink wrap the leads on the caps. They didn't look that bad until I took that photo :bigeyes:

Thanks for the kind words !