Quote:
Originally Posted by Kamakiri
Just to clarify, I did a soft start on a variac, but not too slowly....I took about 20 seconds to bring it up to voltage. Initially, the reading was 305 volts, and dropped to 235 on the first try, with the one resistor in place. The voltage reading was tested at the B+ point that was on the schematic on the previous page in this thread.
I then shut it down, put in a second resistor in place, then again with a quick variac power up, the reading briefly stabilized at around 253 volts. I noticed that I had a full raster, snow, and static in the audio....exactly the way it should be. Observed it only for a few seconds, then went back to the meter and noticed that it started jumping all over the board, ranging from 240-260 volts. When I caught a light odor of something, I shut the set down immediately.
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I'm still trying to understand this sequence... it appears that with one 39 ohm resistor in series with the diodes to the B+ test point, there was no problem other than the B+ voltage being slightly too low? The resistor did not overheat ... correct?
Then you put a second 39 ohm resistor in parallel with the first to increase the B+, which it did, but then the voltage started jumping around and one resistor started smoking? Was the first resistor still ok? Putting the two identical resistors in parallel would have reduced the voltage drop across the resistor(s) and, therefore reduced the power dissipated by the resistors(s) as well as splitting that power between the two. Neither should have overheated. Perhaps the second resistor was defective?
If it were mine, I would try again with a fresh resistor and monitor the current in series with the resistor pair.
jr