• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Hum / oscillactions in EL84 push-pull amp

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Since both channels are equally affected, something like this seems most plausible to me. I'm pretty sure it's not external interference, as the measurements at another location were exactly the same. The amplitude of the oscillations is indeed very small and does not influence the sound reproduction noticeably. I am simply tempted to find or explain the cause of such problems/phenomena.


This is a worthy goal, and if I have inadvertently expressed myself poorly please forgive and accept an alternative description:


By "external", I only meant external to the intentional signal path. Noise sources in the power supplies are a possible example. You've ruled out distant noise sources, so your task is easily manageable. You see these pulses at twice AC line frequency? That's a good clue. What can you safely see with that software scope?


It looks like it might be a powerful tool to look at this issue, but you need to maintain a safety protocol looking into high Voltage power supplies.


All good fortune,
Chris
 
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