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"What is odd is the fact that the CRT looses focus whenever a waveform is displayed. I do notice that the HV to the CRT does drop by about 100 Vdc when the intensity is full CW. Don't know if it is normal or not."
I believe that I am seeing evidence of an oval spot in both pictures... note how the sweep line seems to "taper" off at each end.
I suspect that some drop of HV at full beam current (perhaps 100uA or so?) would be fairly normal.
"I am wondering if it may be leakage from the focus and intensity controls to the chassis given the originals were mounted using an insulator to isolate the variable resistor case from the chassis and the knobs were mounted to a plastic shaft."
I was about to ask about something like this... I have seen it before, a pot with HV on it may well develop leakage to ground, throwing the voltages in the divider string off considerably. Since the spot is quite oval in the Horizontal direction, perhaps the voltage on the astigmatism electrode is way off as well.
"Now I can connect another 5ADP* series CRT in parallel with the one in the scope and I get proper focus. "
Huh ? So if you connect two tubes at the same time to the scope they both look ok?
jr
Last edited by jr_tech; 01-23-2011 at 02:55 PM.
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