[AMRadio] BC 375 Repair


Jim Wilhite w5jo at brightok.net
Wed Nov 27 08:12:13 EST 2013



>> Yeah that stuff is Glyptol (sp?) a WW II version of Locktite. You may 
>> be
able to flood the shaft / knob bushing with something like Flux Remover 
from
a spray can or MEK. I don't think Lacquer Thinner will do any good, just 
be
careful not to get any solvent on the plastic knob.....
?
Bill AD5OL>>

I had success removing the kilocycle disc dial on my 75-A4, which uses
similar stuff, by making a special attachment to a small soldering iron. 
I
used a brass screw with threads the same as those on a tip that would 
fit
the iron (6-32 IIRC), but much longer than a standard tip. You may find 
a
stock tip long enough. Just make sure it is small enough to pass through 
the
set screw hole in the knob without contacting the plastic. File the tip 
to a
point so that it will fit into the hexagonal hole meant for the Allen 
driver
(or Bristo if that's what it uses). Then apply a fairly large dab of 
heat
sink compound to the tip, let the iron come to temperature, and 
carefully
insert the tip into the hole in the head of set screw and hold it in 
place
for a few minutes, long enough for enough heat from the iron to transfer 
to
the screw, via the heat sink compound, and soften the Glyptol or 
whatever
it is. Carefully remove the hot iron and immediately insert the proper
driver to rotate the screw, and it should easily break loose. You might 
use
a small tool to dab some sink compound onto the screw head before 
inserting
the iron, in addition to the dab on the tip, to assure the best heat
transfer.

In the case of the 75A-4, I fabricated a heat shield, using a piece of 
thin
cardboard sandwiched between two pieces of aluminium foil to keep the 
hot
tip from damaging the plastic disc on the kilocycle dial. The Bristo 
screw
head was hopelessly rounded out because someone had attempted to turn it
using an Allen driver. I tried several rotary drills until I found the 
size
that would fit inside the hole and firmly grab the screw, but I did not
attempt to turn it. I noted the drill size and then ordered from
McMaster-Carr a left-hand drill (one designed to be rotated in reverse 
of
the normal clockwise direction when drilling a hole). When it arrived, 
I
heated up the set screw as described above, with the heat shield in 
place,
and then used the reverse drill chucked into a small handle to grab the
screw inside the hole and back it out. The reverse drill bites into the
screw when turned to loosen the set screw. A conventional drill bites 
into
the hole only when rotated to tighten the screw, so one of those won't
work. The special drill wasn't terribly expensive, so I ordered two just 
so
I would have a spare in case I broke one. The shipping cost more than 
did
the drills. The "handle" I used was a short brass rod, with a hole 
drilled
in one end, slightly larger than the shank of the #49 drill, and glued 
in
place with JB Weld.

But hopefully, you won't have that problem, and a regular Allen driver 
will
work. I don't think they used Bristos in those units.

Don k4kyv




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