With my solid state replacement for the 83 rectifier tube in place, I found that the tester delivered no plate voltage to the circuits - one of the two potentials that are handled by this tube. Time to carefully probe all the voltages present at the tube socket, to determine if I have something burned out in the main power transformer.
The rectifier tube (type 83) is actually a dual diode. Each of the two plates is connected to an opposite polarity AC winding on the power transformer delivering +170V. There is a filament winding where the rectified DC output is the center tap and each side delivers 2.5V AC at opposite phase to light the tube filament.
|83 rectifier circuit|
|Solid state replacement for 83 tube - large pins are the filament|
The only thing that didn't check out was the plate voltage on the tube socket when I pushed the gm test button P4 - it should jump to 150V but it did not do that. Having verified the voltage is produced by the rectifier tube, it is just a matter of tracing and checking each step in the circuit from there to the plate pin of the tube socket.
I could have bad contacts on the push buttons or rotary switches that connect the plate voltage to the appropriate socket pin, or it could be a problem with some components in the path. I am overjoyed that this is working so well already, particularly that I don't have a bad power transformer.
Unfortunately, the path from the point where the rectifier delivers 150+ DC is where one of the deviations exists between the TV-3/U and my TV-3A/U unit. As well, there is no "large/small" signal switch on my unit, but the predecessor allows selection of 1V or 5V AC signal on the grid when testing transconductance.
I also discovered that P4 is not the gm test button on my unit - there is a row of pushbuttons with only a couple marked. It think it is better that I wait until I know what is what before I decide whether the plate voltage is delivered or not, plus I need an accurate schematic. I will set this aside until I get the manual and new DMM.