[dtvmcdonald]

While running through a test of all my old tubized gear I
tested this thing. It was not working as well as last year
(i.e previous post). I never was able to get it working well with adjustments, even
in the brief periods of sunshine. It did work.

I spent four days trying to diagnose the problem with no success.
It made pictures but the shading was bad, and the horizontal
scan was too wide, i.e. the actual picture area was too narrow on the monitor.

I'm was never able to find what had gone wrong. All voltages and waveforms looked OK per the schematic.
I never got a reply to my query in the post a year ago for a real military manual. So I have no reference for most voltages.

Then the cathode resistor in thge 6L6 horizontal output stage started
smoking. I quickly measured the voltage across it and it was as normal, 17
volts AC ... there is no known correct DC value, but it was rather high.
A NOS 6L6 changed nothing. The resistor and its bypass measured as per the schematic. A new resistor didn't get hot
and nothing changed ... so I have no idea the cause, and must attribute it to a loose flake of
solder shorting something, that fell out while doing the checks.

The HV was only -700 volts, rather low (iconosocpe rating is 1250V), and
the waveform of the horizontal drive at the yoke was wrong at the first part of the scan. I fixed this somewhat by
tweeking the resistor-capacitor series pair across the yoke ( 470 ohm, .02uF) ( it was a small tweek)
and removing the 1 Meg resistor I had installed in series with the
HV rectifier diode. I tried adjusting the width control, but the best setting was at the low inductance end. So I
gave up and added a 2.56 mH "RF choke" across the width coil. This fixed those problems and got 800 volts HV-,
a passable value. It still took a LOT of tweeking to get the values of the two signal
few-pF ceramic trimmer caps set right.

Another problem is that the sync pulses are a larger fraction of the
period than NTSC specifies (its actually 262@60p), because it was designed for 40 Hz, not 60. The overall shape of the
vertical scan was a bit wrong. Adding .22 uF to the horizontal output cathode fixed that and got 900V HV-.

Once done, the picture was a teensy bit better than last year
(not enough better for a new picture here), and it runs on almost all monitors.

I'm still looking for the military repair manual (though, of course, in intended use repairs were, ah, the opposite of what was desired).