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Old 06-19-2016, 06:03 PM
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dtvmcdonald dtvmcdonald is offline
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Join Date: Nov 2012
Posts: 1,191
I have a very complete set of "before" pictures. I'm rather tired out this evening, so its
unsafe to do more work. I'll try to take the "after" pictures and ones of the power supply,
which still lacks the sync modifier suggested bu McVoy.

Today was devoted to troubleshooting (electronic tests only ... the first
iconoscope test will be tomorrow).

The power to the iconoscope filament was inadequate. It took quite a while to
prove this, as I have no AC voltmeter that works at 16 kHz. I had to
use an analog scope or compare filament brightness between two identical tubes,
one on the camera and one on 6.3vac. Tomorrow I'll bring a digital scope that can
do true RMS AC. The problem was that the screen resistor, supposed to be 82K,
was 106K. This caused the screen voltage to drop to zero at high power, thus
limiting. Even 82K did not work, I eventually used 60K.

Then I worked more on the video amplifier chain. It was horrendously microphonic,
as if there were a broken lead connection. There was., onC154, a 1000pF mica in series
with a 0.05 uF film cap (??? WHY ... its not a high voltage area.?) It had a lead
that was broken off about 1/2 millimeter inside its case. This was not easy to find,
though tapping and poking eventually found it.

Another source of problem was found in a noisy gain pot. This is wirewound 10K.
At least for the moment is was fixed with DeOxit ... you have to take the
case off and flood it, as the noise seems to come not from the wiper on the
resistor element but on the connection of the wiper to the outside.

The shading pots are similar, but are not so bad.
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