Hey. I have a dynakit stereo 70 and just got a matched set of 4 tubes and am learning to bias them. I can't seem to get the channels biased at over about .765 on the 2v setting.
What do you mean by ".765 on the 2V setting"? Setting of what, your voltmeter? Is .765 the voltage, or percentage of scale? Is it the same on both sides? If it is a fraction of the total scale, that's about 1.53V, which is low but not terribly unusual for a tired bias supply. It's also possible that your sockets are not well-connected to the chassis, and if so, you may not be grounded well enough.
If it is truly .765 volts, as assuming your amplifier is stock, and still has the 15.6 ohm bias resistors, then I would suspect a misreading, very tired or wrong output tubes. Assuming the amp is stock AND the reading is the same on both channels, then I would suggest that the selenium rectifier and/or the bias supply filter caps need to be replaced, because those are now 50+ years old. Selenium rectifiers tend to degenerate in such a way to increased forward voltage drop, which can and frequently does prevent you from getting enough current.
Overall, anything that is stock of this age is likely to need a complete refurbish to work reliably. But I would at least refurbish the bias supply circuit.
Brett
