thanks

I still need a manual for this gizmo. Web searches are futile.

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).

One astounding tidbit. Looking at the severe noise (the S/N of a sunlit scene
is like 2:1) I noticed something and measured the frequency response. That's the frequency response looking at the width and shape of a full dark-to-light sharp edge or light-to-dark or stripe test patterns. The 3dB down point.

Its 8 MHz. That's eight megahertz. Eight, 8, e i g h t. And it shows on the high end
Ikegami monitor I'm using. Why would they make such a thing when it was supposed
to feed a transmitter that surely not that wide, nor displays that wide either.

It does demonstrate how sharp iconoscopes can be, such as the talking one in Japan :-)

Given it's a WWII guidance camera and that the military had a lot of leeway on how it used RF during the war it's possible the engineers foresaw the possibility of having a channel wider than 6MHz and higher scan rates for increased resolution for some special application and gave the video circuits enough bandwidth that one could swap the transmitter and tweak the scan to achieve that easily.

Is the horizontal scan rate 15750? If it's slower, the bandwidth will be less by the same ratio even though the horizontal resolution is high.

"

Yes, its ~15750 Hz and ~60Hz, locked together, not locked to line.
Put another way, its 262+-1 @ 60p, the latter not locked to power line (since
all the power lines are DC).

But that's immaterial for my main measurement, which actually measured
the rise and fall times of sharp edges in an image. The ringing frequency of the noise agrees.

The lower the horizontal scan rate the higher, not lower , the resolution in pixels. In any case, I found a statement of 4.5 Mhz bandwidth for that system, and double sideband AM, black at 100% up modulation, but it didn't say whether the 4.5 Mhz was the baseband or the DB channel width. Somebody with a transmitter .... or the manuals ... should know. But nobody has manuals.

I've found that trying to run at NTSC rates rather than 14kHz and 40Hz
(progressive) was what was causing big problems with the shading corrections.

Adjusting some cap values and the width coil value, plus adding a small vertical linear correction directly to the output stage fixed that. It now makes a fairly good picture,
still with sone shading problems even if direct sunlight scenes.

It was not drifted component values.

Nice!

Pictures???

The quality in photos has not changed much. Its more visible direct, because you can see the high frequency noise better.
Photos need more than one field exposure, which averages it out.

Got it. Was wondering if a shading improvement was visible.

Not for that scene in broad saylight.
I'm still working on the white stripe near the left edge. This is caused by
ringing in the horizontal deflection pulse used for shading. I was never able to get completely rid of it at 15750 Hz.