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I have a BD on the bench that came with a somewhat loud hum. After initial inspection, I changed two leaking filter caps - C34 (first series filter) and C45 (pi node). Also R82 (220K stabilizing voltage resistor from first node, which was open).
Fired it up to find hum was there yet.
Now the odd stuff: hum lessen from few minutes of warm up, to completely disappear (to normal levels of background noise) in about 15 minutes. Turning off/on immediately don't bring the hum back, amp needs to cool down a bit to show it again.
Hum only appears in the clean channel, but it's not affected by volume settings; pulling out the pi tube kills it though (yep, already changed the pi tube). Power tubes are a pretty good match also.
Ripple from filter caps seems usual: about 2VAC before choke, to next to nothing over the preamp node. I piggybacked a new cap to make sure. No 120Hz appears on the output either.
Honestly, I'm running out of ideas. Anyone ?
Fired it up to find hum was there yet.
Now the odd stuff: hum lessen from few minutes of warm up, to completely disappear (to normal levels of background noise) in about 15 minutes. Turning off/on immediately don't bring the hum back, amp needs to cool down a bit to show it again.
Hum only appears in the clean channel, but it's not affected by volume settings; pulling out the pi tube kills it though (yep, already changed the pi tube). Power tubes are a pretty good match also.
Ripple from filter caps seems usual: about 2VAC before choke, to next to nothing over the preamp node. I piggybacked a new cap to make sure. No 120Hz appears on the output either.
Honestly, I'm running out of ideas. Anyone ?
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