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Is this one of those Setchel Carlson portables? I am working on one of these and had the same issue. I tested and changed tubes to no effect. I had also tried new power supply diodes. I had the correct new electrolytics in and still had the hum. All resistors in the power supply circuit were the correct values. What I have finally done is add another 100 ufd filter in the main DC supply circuit. This seems to have fixed the problem, but I am somewhat worried about surge current when the set powers up.
The hum was in the power supply area and displayed very well on an oscilliscope.
Another comment about this set is that the CRT mounting is horrible. Only the ring around the front holds the CRT in, there is no support for the back portion of the CRT.
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