[Milsurplus] Capacitor Question

[J Forster]

The technique works fine as long as there are not voltage dividers between B+
and ground or the B- is not designed to float below ground (as in the R.1155).

If there are voltage dividers, you must calculate the expected draw and allow
for that. These can be dicey as the decoupling caps can be overvoltaged if the
tubes are not powered.

Sometimes, internal shunt regulator tubes can be damaged due to overcurrent by
the technique as there is no downstream load.

Bottom line, powering a set with the filaments off is a good idea, but there are
some caveats and a careful look at the circuit before flipping the switch is
advisable.

Best,
-John




Al Klase wrote:

> Guys,
>
> This is an excellent troubleshooting methodology, to root out problem
> caps.  It's especially useful in cases, like ARC-5's, where its really
> inconvenient tp shotgun the capacitors.  Everybody needs a good bench
> supply.
>
> Al
>
> Marty Reynolds wrote:
> > I'd add this tho.  Make sure no filament supply.  Apply more than design
> > B+ to rx thru a current limited supply.  Like 400vdc w. seriesed 25K
> > resistor.
> >
> > Measure drop across resistor & if zip, you & the purported micas are fine.
> > If big drop, look @ ckt. for shunt across B+ line.  If found then lift it
> > & try again.
> >
> > If drop still there, start rattling thru all B+ isolation resistors to
> > ferret bad bypasses.
> >
> > I reported this months back as a fast way to revive a long-dead BC-455.
> > Found only one bad "in-can" bypass.
> >
> > Recent example is a BC-224 fm weeks back.  Old one, BC-224h by RCA - sn
> > 98.  Must have been in a lean-to for years.  Lotsa outside mud.  But
> > after lifting RF gain ctl fm gnd, NO drop across current limiter R!!!
> >
> >
> >
> >
> >
> >
> >
> >
> --
> Al Klase - N3FRQ
> Flemington, NJ
> http://www.skywaves.ar88.net/
>
>   ------------------------------------------------------------------------
>
>   Al Klase <al at ar88.net>
>
>   Al Klase
>               <al at ar88.net>
>   Flemington
>   NJ
>   Additional Information:
>   Last Name      Klase
>   First Name     Al
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