04-12-2014, 09:43 AM
I made a checklist for all of the previous suggestions. But first I removed a capacitor which I put in because I thought had been added in a later run--but it was not in Service Bulletin 234. The volume of the hum dropped at least 50 percent.
I went through each item on my checklist except for verifying the polarity of C58 and C59. I didn't want to open the rebuilt cans, so I disconnected those capacitors and temporarily wired in new ones of the same values, being certain that the polarity was correct. This made no change in the hum, so I assumed that the C58/59 cans had been wired correctly.
Then I wired in new capacitors which were twice the values of the original C58/59, and there was no discernable any hum at all.
I think it's ready to go back in the cabinet, but while it's still on the bench, I'd like to ask about one more issue which I bypassed when I was first checked chassis voltages several months ago. These were my readings with 124VAC line voltage.
[Image: https://lh5.googleusercontent.com/-D9Z_y...520645.JPG]
I asked about this briefly on another forum, didn't resolve the issue, but proceeded with the restoration because the radio seemed to be working well. I just rechecked the 85 plate, and it's still 44V. This shows the voltage peripheral to the plate, but it's beyond my understanding why the 267V drops to 44V instead of the expected 82V.
[Image: https://lh5.googleusercontent.com/-qBwpK...520645.jpg]
So, is there any reason I shouldn't put higher-value caps in C58 and C59?
Should I be concerned with the low 85 plate voltage, or should I leave it alone?
I went through each item on my checklist except for verifying the polarity of C58 and C59. I didn't want to open the rebuilt cans, so I disconnected those capacitors and temporarily wired in new ones of the same values, being certain that the polarity was correct. This made no change in the hum, so I assumed that the C58/59 cans had been wired correctly.
Then I wired in new capacitors which were twice the values of the original C58/59, and there was no discernable any hum at all.
I think it's ready to go back in the cabinet, but while it's still on the bench, I'd like to ask about one more issue which I bypassed when I was first checked chassis voltages several months ago. These were my readings with 124VAC line voltage.
[Image: https://lh5.googleusercontent.com/-D9Z_y...520645.JPG]
I asked about this briefly on another forum, didn't resolve the issue, but proceeded with the restoration because the radio seemed to be working well. I just rechecked the 85 plate, and it's still 44V. This shows the voltage peripheral to the plate, but it's beyond my understanding why the 267V drops to 44V instead of the expected 82V.
[Image: https://lh5.googleusercontent.com/-qBwpK...520645.jpg]
So, is there any reason I shouldn't put higher-value caps in C58 and C59?
Should I be concerned with the low 85 plate voltage, or should I leave it alone?