Howdy folks,
Got a friends Dual rec on the bench. Noticeable hum on both channels But i feel like im on a goose chase with this thing.it seems to be moving around when looking for it on the scope.Hum disappears when first tube is pulled. Did mesa use V1b for something? i cant find anything on the schematic.
Checked all grounds and replaced all the tubes. Heater winding centertapped.
Scoping the switching legs of LDR1/2/3/4/5/6, it seems 1/2/4 seem to be leaking a couple mv of signal when closed, strumming a guitar. the rest show nothing. Would it be better to test the LDRs on their LED side? (voltage drop etc etc)
Do optocouplers even leak or would that be a switching supply issue?
Lastly V3a's Plate is quite noisey compared to other plates. the resistor measures ok, BUT i just read on this forum that mesa laid resistors over other traces and caused problems. This amp is from 1996. Goona go look into that now.
Schematic link:
https://goo.gl/images/EZuu6O
Got a friends Dual rec on the bench. Noticeable hum on both channels But i feel like im on a goose chase with this thing.it seems to be moving around when looking for it on the scope.Hum disappears when first tube is pulled. Did mesa use V1b for something? i cant find anything on the schematic.
Checked all grounds and replaced all the tubes. Heater winding centertapped.
Scoping the switching legs of LDR1/2/3/4/5/6, it seems 1/2/4 seem to be leaking a couple mv of signal when closed, strumming a guitar. the rest show nothing. Would it be better to test the LDRs on their LED side? (voltage drop etc etc)
Do optocouplers even leak or would that be a switching supply issue?
Lastly V3a's Plate is quite noisey compared to other plates. the resistor measures ok, BUT i just read on this forum that mesa laid resistors over other traces and caused problems. This amp is from 1996. Goona go look into that now.
Schematic link:
https://goo.gl/images/EZuu6O
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