06-12-2020, 09:32 AM
You are correct on the 10K resistor, it is part 26 not 20. My diagram is a little fuzzy. So now I see a couple problems. First, the B+ is high, probably due to the increased filter capacitor value and higher modern day line voltage. You can probably tackle that later with 22mfd caps instead of the 33. Second, the plate voltage at pin 3 of the XXD should be around 70 volts given the higher B+ but it still should oscillate. The value of 26 might be too high, use your dmm to measure the resistance.
It looks like the oscillator starts running when you touch pin 4 with the probe. This suggests that a capacitor in the XXD oscillator triode is out of tolerance or the triode is bad. It could also be a bad pin connection so you might want to re-check the pins of the tube. The loctal tubes are noted for pin corrosion. I use steel wool then clean with alcohol. Don't use water on loctal tubes, it removes the lettering on the glass.
It looks like the oscillator starts running when you touch pin 4 with the probe. This suggests that a capacitor in the XXD oscillator triode is out of tolerance or the triode is bad. It could also be a bad pin connection so you might want to re-check the pins of the tube. The loctal tubes are noted for pin corrosion. I use steel wool then clean with alcohol. Don't use water on loctal tubes, it removes the lettering on the glass.
