I have a Vox AC 30 that I built from an old Baldwin organ amp that hums even without tubes. I suspected heater wiring since this is the only amp I have with no CT for the heater winding but chopsticks revealed nothing. It does have an artificial CT via 2 47 ohm resistors to ground. Could this cause the hum?
Moving the OT has cured the hum. Mostly.
Moving the OT has cured the hum. Mostly.
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Moving the OT away from the PT should help, and it also is important that the iron laminations of the two transformers be in different orientation. It may look neater to have them all facing the same way, but that is the worst situation, you want them 90 degrees different. That is why in an amp like an old Fender, the power transformer is mounted in a hole in the chassis with horizontal laminations, while the output transformer is mounted vertically.
With no tubes in it, the 6v wiring shouldn;t matter. I suspect your hum is the field of the PT coupling into the OT windings.
With no tubes in it, the 6v wiring shouldn;t matter. I suspect your hum is the field of the PT coupling into the OT windings.
It hums either way. I am using shorting jacks. The chassis just is too small and the transformers are too close together.
I have had the same issue with small chassis. I tried a different power transformer and the hum went away.
If the transformer your using is old it could have shorted turns creating a large electromagnetic field.
Also if laminatations are loose you will get noise.
If the transformer your using is old it could have shorted turns creating a large electromagnetic field.
Also if laminatations are loose you will get noise.
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