Hammond b-3-,c-3-, rt-3 hum?!?

[Guest]

Hi</p>

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Im a guitar/amp tech in Europe , but i try to
repair anything that gets in my way :) So recently i stumbled upon an
rt-3 (its bassically the same as a b3 or c3 right?) that has a lot of
hum.All the tubes on the ao-28 preamp have been replaced.Bassicaly the
hum increases when i turn on the percussion from soft to normal or
increase the volume with the expression pedal.Anybody have any advice
where to start looking?When i pulled out the v4 (12ax7) the hum was
still there .I checked the resistors around v3 and there all within 10%
of the value.Has anybody had any similar problems?</p>

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Thanks in advance
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[Guest]

Re: Hammond b-3-,c-3-, rt-3 hum?!?



check the tubes metal shields
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[Guest]

Re: Hammond b-3-,c-3-, rt-3 hum?!?



Tube shields?There on the tubes ,what else about them should i check?</p>

I have measured the dc voltages and they are kinda low. The voltage after the V8 6x4 ( measured on C56) is 295 volts, the diagram says it should be 375 volts.
Subsequently all other voltages are lower ,about 23 % lower,Could the voltage difference cause the hum?
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[Guest]

Re: Hammond b-3-,c-3-, rt-3 hum?!?



Replace electrolytic capacitors in power supply.
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