I appreciate this discussion of flyback and HV circuits, it is good to learn from others with more knowledge than I have with these early sets.
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Originally Posted by Electronic M
Chris, one thing that now comes to mind is that you are calibrating the horizontal and HV system with that set on a test jig (right?)
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Yes, I am using a jig, and you made some good points, thanks. I will indeed re-check everything once I move the chassis to the cabinet.
Since I had the overheating/meltdown/arcing with the set powered on for a relatively short time (20 minutes or so perhaps) compared to having it run an hour or more several times previously without a problem, I suspect that I caused the overheating by running the horizontal circuits off-frequency too long or too far, as I did the waveshaping adjustments.
I did a new set of tests today, including running the chassis longer and at 110-115 volts, with no problems seen. After being powered on for over 20 minutes, the flyback was just low to moderately warm, certainly not warm enough to cause wax to melt off if it was present, and no warmer at the arcing point than elsewhere, so it seems to have survived.
Bob, I am not sure why I was seeing that 120mA H output cathode current reading, and in fact today's reading was 80mA for a few minutes before going up to closer to 200mA while I was looking elsewhere during testing. I have to suspect my Simpson meter (maybe dirty contacts; I have never used its current function since restoring and testing it a year or more ago), since there was no change at all in the appearance of the picture before and after the displayed current change. I checked the current with and without a 0.1uF/630V capacitor across the meter connections, and I also tried my Fluke DMM with and without the capacitor. Neither meter showed any difference without the capacitor, so I will say it is not needed here as some of you already said was likely. The meter readings (all of this was after the Simpson readings "jumped", and they stayed consistent once they did that) were: Simpson ~195mA at ~108V line voltage (from the Variac) and ~205mA at ~115V, Fluke 188mA at ~108V and 198mA at ~115V. I did verify that the H linearity coil was set for lowest current (well, as soon as it went even a couple of mA higher, I stopped and went back, in both directions; I had already adjusted it for a bit lower current yesterday).
I will plan to do current readings again after I put the chassis in the cabinet, too.