[ARC5] BC-946 capacitor plates shorting?

[Rich Post]

I have successfully done this using a pair of incandescent 5 watt night
light bulbs in series as the current limiter. The radio had been subjected
to coal dust.   Yes, lots of tiny sparks.

Rich KB8TAD

On Tue, Nov 9, 2021 at 10:27 PM Tom Lee <tomlee at ee.stanford.edu> wrote:

> Nah. Low-power resistors protectively vaporize if overloaded. It's a
> feature. ;)
>
> Tom
>
> --
> Prof. Thomas H. Lee
> Allen Ctr., Rm. 205
> 350 Jane Stanford Way
> Stanford University
> Stanford, CA 94305-4070
> http://www-smirc.stanford.edu
>
> On 11/9/2021 19:20, Scott Robinson wrote:
> > I'll add that the resistors should be 10W rated.
> >
> > /scott
> >
> > On 11/9/21 5:53 PM, Scott Robinson wrote:
> >> If your short in the tuning cap is persistent, try this, which I have
> >> used and it works:
> >>
> >> 1) Disconnect anything in parallel with the tuning cap.
> >>
> >> 2) Find an adjustable 300V power supply, doesn't have to be regulated.
> >>
> >> 3) Connect a 10K resistor in series with the hot lead, and connect
> >> that to the floating side of the cap. Connect the low side of the
> >> power supply to the cap frame.
> >>
> >> 4) Turn the voltage up until you see teeny sparks as you rotate the
> >> tuning cap. run the cap back and forth until the sparks cease, and
> >> maybe blow some compressed air through it, too. Raise the voltage
> >> some more and repeat. If you get 100-200V or more with no sparks,
> >> you're done. You can try a smaller resistor value ( maybe 3k) if you
> >> like.
> >>
> >> This will fry any metal whiskers present.
> >>
> >> FWIW,
> >>
> >> Scott Robinson
> >>
> >>
> >>
> >> On 11/9/21 4:59 PM, J Mcvey via ARC5 wrote:
> >>> Another possibility is that is has some debris or has grown metallic
> >>> hairs ( yes this really happens!).
> >>> The quick approach would be to crank up a compressor, if you have
> >>> one, and blow the debris out while the plates are unmeshed. This
> >>> works about 75% of the time.
> >>>
> >>> BTW , you will have to remove the coil pack  if you want to do an
> >>> ohm check, otherwise you will read the low resistance of the
> >>> parallel coil.
> >>>
> >>>
> >>>
> >>> On Tuesday, November 9, 2021, 06:33:57 PM EST, Kenneth G. Gordon
> >>> <kgordon2006 at frontier.com> wrote:
> >>>
> >>>
> >>> On 9 Nov 2021 at 14:17, Waldo Magnuson via ARC5 wrote:
> >>>
> >>>  >    Any fix suggestions would be appreciated.  Removing the gang
> >>> capacitor looks messy.
> >>>
> >>> Actually, it isn't difficult at all, since it was designed to be
> >>> easily removable.
> >>>
> >>> There are 4 larger screws in a box pattern on the front-panel which
> >>> hold the cap to it.
> >>>
> >>> You will first have to remove the inner cover over the cap, then
> >>> unsolder 3 wires, one of each
> >>> which goes to a section of the cap. They are easy to reach.
> >>>
> >>> Then unsolder the wire which goes to the antenna post.
> >>>
> >>> Remove the 4 screws, then simply lift out the cap.
> >>>
> >>> FYI, the tuning capacitors from the MF receivers, either the BC-453
> >>> or the R-23/ARC-5 are
> >>> identical to the BC band tuning cap.
> >>>
> >>> If your cap is damaged, one from either of the two receivers
> >>> mentioned above can replace it.
> >>>
> >>> But, as others have mentioned, an ohm-meter will tell you if/where
> >>> it is shorted. As also
> >>> mentioned, it may simply be that the cap is no longer grounded.
> >>>
> >>> Ken W7EKB
> >>>
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