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well I decided to take one more stab at the HV regulation..
I have the "early" production version of the 20C1x38 chassis, my service notes showed the changes from the early to the late, one of which was HV regulation
I rewired the HV pot per the late version. the only diff was the output from the varistor was directed to the unused side of the pot, and the input for the grid bias of the 6HS5 tube was moved to the center wiper. the 1 meg resistor was left in place. This results in the pot as a true voltage divder (+ one side, ground thru the 1 meg on the other) rather than acting like a reostat with only one side and the wiper in the circuit.
I also added a second varistor piggy backed to the replacement (actually I just reused the old one I had taken out) This was done on the top of the chassis after the initial trial did not have good range.
I had tried the piggy back method before the rewire of the pot and it did not help much, some but not much. So I know the rewire was the key.
I am not able to dial in the HV to the exact amount specified and its very near the middle of the pot setting.
My guess is the varistors are not very precise, I know this since I tried a few by just putting them to a mA meter and dialing in up to 450v. They were very different readings for the several SAME rated ones I tried. These were NOS so dont know if they just age poorly or if its just the way it is.
But now I am happy, I get rock solid HV (very little movement regardless of the screen brighness) and I am able to lock it in right at 24.5kv.
I just have to work that speaker issue out and I can button it up for good.
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