[Milsurplus] BC-611 Repair Tip

[Robert Downs]

I have over the years found many 611's (but not all) with the plastic tuning cap cover shrunken badly enough that if you attempt to tune the transmitter, you will short rotor and stator plates, ruining the capacitor.  None, however, have been as bad as the one that you encountered.  Most were repaired by cutting about half of the plastic off until is was safe to try to rotate the rotor.  Two or three were frozen badly enough that I ended up having to replace the capacitor with one salvaged from a junk chassis.  But most were cleaned up in place.

Robert Downs


-----Original Message-----
From: milsurplus-bounces at mailman.qth.net [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of David Stinson
Sent: Thursday, October 1, 2020 09:36
To: milsurplus at mailman
Subject: [Milsurplus] BC-611 Repair Tip

While working on the previously mentioned BC-611s,
I was lubricating the shafts of the air variable caps when
one of them seemed to bind.  I removed it and found the
insulating covering over it had shrunk with age and
was binding/bending plates.  I pulled the cap:

https://photos.app.goo.gl/8bUR6ZAWif4yPxu17

It turns-out finding this was a "blessing in disguise."
Removed the plastic and found heavy corrosion on
every mechanical and soldered part of the cap.
The red arrows point to locations which showed
open connections to their respective parts.
None of the parts showed any continuity between
them and their respective connection points,
not even the "soldered" rotor leaf spring.

https://photos.app.goo.gl/C8Y8RA8Qx1myX7Hf9

Repaired the plates, then carefully scraped
the lead-oxide bubbles off the
the rotor leaf spring (away from your face,
since you don't want to ingest that stuff).
Re-soldered the two stator posts and
the leaf spring contact.
This left a bunch of black residue and little balls
of solder, which I cleaned away with Naptha,
since we don't want those lead bits getting
in the plates.  Once the naptha evaporated, used
De-Ox-It on the rotor leaf spring and oil on the
shaft.  It took two doses of Deoxit and dozens
of turns on the rotor shaft to make the contact
reliable.  Hasn't failed since.

Before re-installing, the stator posts solder
point on the front face of the cap must be
insulated.  A cut piece of black tape will do.

I think I'm going to pull the caps from the
other rigs.  Better to fix them now than
have to do it later.

GL OM ES 73 DE Dave AB5S


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