CRV59-AAE Military Iconoscope Camera restoration

[dtvmcdonald]

Originally Posted by old_tv_nut

Just on general principles of poking around, have you checked R114 and R126?

Yes, and they are new. I've checked all bias resistors. I've studied all the
bias voltages as it heats up. They do drift, but the key grid-cathode bias
voltage does not, and all drift in sync and in small amounts. The bias
in any case need far more adjustment than the drift.

I tried checking drift of filament voltage while running by comparing
the brightness and color of the tube in the camera to that of my dead
1846 running on 60 Hz and they are rock stable. I measured
the heater voltage both by comparing the brightness to the other tube
both on 60 Hz and the other one on 60 HZ and the camera one on
15750Hz, and also by measuring the camera tube voltage with a digital
scope across the filament with the HV disabled, then calculating the
RMS voltage from the scope trace (its sort of a square wave). I can't
get the voltage up to 6.3 but is very close and does not drift enough
to cause the problem.

Of course, both tubes could be equally bad by chance. But its
odd that of three tubes that have look-alike getters one does not
work at all and two work sort-of, and the same.

I've tried swapping 6AC7s around to no effect.