I am a new member here. My name is Mike. I recently acquired a 1967 ST-70, with both the DIYTube driver board, and the SDS Labs cap board with solid state rectification. The unit seems to work fine, but I can not get it to bias properly. I am a EE who recently retired after 30 years at Collins Radio, but never worked on tubes until now. When I first got the unit, both 10K bias pots were full counterclockwise. The bias all four Svetlana EL34's was above 60ma. rotating clockwise only increased the bias voltage, so I stopped, and shut the unit down. Resistance checks at J6 and J21 read 10K-14K as I rotate the bias pots. The bias pots are both dated 1967. All four bias resistors measured 10.5 ohms. I am a little lost on where to look next. Any help would be appreciated. BTW, I tried to use the search function, with no luck.
Mike