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I'm getting about 2.75v from the filament transformer for the tube and an additional 5v from the end of the winding going to the grid (7.75v all together). So, it's probably a 7.5v transformer with a tap coming out about 1/3 of the way.
With respect to the center tap, the voltage at the grid of the thyratron is 3.75vac, that's after going through the 9K impedance.
Also, how can you have negative voltage from a transformer??? It's AC.
Update: I just tried hooking up a 9v battery to the grid (in series with the 51K ohm resistor). It worked!! The battery measured 8v, and it was just enough to turn the tube off and work with the mystery control. Sometimes, it would activate momentarily, but increasing the battery voltage would probably correct that. The control does seem to be missing a pulse here and there, but it's actually working! Now for the hard part, I have to fix it correctly to work without the battery.
Last edited by ghjkl67; 06-10-2015 at 07:00 PM.
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