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Power Supply Woes on AH! Tjoeb '99

Posted by Dan Kinzelman (A) on February 1, 2021 at 03:04:49

Hi everyone,

not sure where this should be posted since I think CD players have fallen far out of favor, but I figure this is where I'll find the most expertise ;-).
I have an old AH! Tjoeb 99 CD player based on a Marantz CD-38 with a tube output stage. A few months ago it started making a nasty ground hum, and I've used my oscilloscope to trace it back to the power supply of the add-on output amp, specifically a fairly symmetrical triangle wave on pins 2 and 8 of each 6922 (respectively, the grid of each tube's first triode and the cathode of its second triode).
I can see no visibly failing filter caps (they are Elnas, which I understand are quality units), and probing under the board is pretty difficult because all the signal and transformer leads are really short, so I'm wondering if anyone has an idea of how to figure out which parts are failing.
There are 4 transistors in the power supply section. My understanding of circuits is pretty basic and doesn't include the function of transistors in linear power supplies. Are these likely culprits, or is it more likely a diode? Or should I just replace all the filter caps and call it a day?
Thanks
Dan

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