Re: unit hums loudly regardless of volume

Thanks for your reply.

Sorry, here's some more info:

There is a power transformer.
Only 1 diode that I could see.
Measured voltages at cap in question was ~150v.
Only 2 tubes - 12AX7 and can't remember the power tube offhand.

There was also some small device which I assume was a transformer that hadd
100mA marked on it. It looked like a trasformer with cooling fins.


"CJT" <abujlehc@xxxxxxxxxxx> wrote in message
news:436100B7.1090008@xxxxxxxxxxxxxx
> 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).
>
> --
> The e-mail address in our reply-to line is reversed in an attempt to
> minimize spam. Our true address is of the form che...@xxxxxxxxxxxx


.

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