Re: unit hums loudly regardless of volume

tempus fugit wrote:

Hey all;

I'm trying to repair an old tube portable record player. When it is on, it
hums really loud, regardless of the volume. I assumed that this must be a
problem with filter caps, but they test OK for ESR and shorts. 1 of the
problems is that there are 3 or 4 in a can, so I don't know what the values
are supposed to be.

Is there anything else that may cause this symptom? I suppose I could
parallel some caps across the existing ones, but I don't even know what the
values are supposed to be.

Thanks



One or more diodes in the power supply (assuming it uses them) is
shorted.  If it has a rectifier tube instead of semiconductor diodes,
then either the tube is shorted or, if it has its own filament supply
(e.g. 5U4), then that supply could be shorted inside or outside of the
power transformer (assuming it has a transformer), although there's a
pretty good chance the tube would be glowing bright red if that were
the case.  If it's all tube and has no power transformer, then you've
got a potentially lethal hot chassis and you'd better be d*mned careful.
Check for shorted line bypass capacitors if it's this last case.

Or it could be one or more capacitors, as earlier suggested, or a break
in some shielding.

As you can surmise, additional information about the circuit involved
could narrow the possibilities (and possibly suggest others).

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