Cleaning Variable Caps

[Steve W8TOW]

So what are some thoughts and suggestions to cleaning variable caps while they
are still installed in a receiver?
I just brought my TMC GPR-90 out of storage. (covered & boxed, but both
caps are "noisy") I used some small amounts of DEOXIT on the ground wipers
for each section and using a tooth brush, gently brushed excess...then took a
Q-tip and wiped off any DEOXIT remaining...

BUT, still a bit of instability when copying CW....what is the best chem to
clean the cap with out removing...

[WQ9E]

Steve,

Are you sure it is the HFO and not the BFO?  The GPR-90 BFO tries to phase lock to the CW signal on even moderately strong CW causing odd instability.  This is one of the reasons I used a Hammarlund HC-10 with mine while looking for a GSB-1.

[Steve W8TOW]

This was while using a newly acquired GSB-1 

SO, it was indeed the "C"....after I had cleaned the caps a little,
the instability improved significantly...but
I'd like to do a better job!
73

[WQ9E]

Maybe you just need to use it more instead of making it feel unwanted on the shelf

Glad you found a GSB-1 and now I can use my newly found (garage sale from electronic packrat) second GSB-1 without feeling guilty about you looking for one.  I picked up a GPR-92 earlier this year and although it has a built in product detector the skirt selectivity is so absolutely lousy it needs an outboard unit under most conditions for CW/SSB so I am using a GSB-1 with it also.

The GPR-92 has six selectivity positions from .5 KC to 15 KC @6 db down but at 60 db down the 15 KC position is specified at a reasonable 27 Khz. bandwidth but the remaining positions vary from 21 Khz. wide @ 60db (the 3 Khz. setting) providing a not so great 7 to 1 shape factor to the .5 kHz. setting which is 27 Khz. wide at -60db resulting in a truly atrocious 54 to 1 shape factor.  It is obvious in use because strong off frequency stations more than a few kilohertz away remain nearly the same strength regardless of selectivity setting.  The skirt selectivity of the GPR-90 is much better, I presume the wide IF setup was part of the compromise needed to allow the GPR-92 to work with the external demodulator which allowed 4 voice or 64 teletype signals to be multiplexed onto a single "channel". 

Like the GPR-90 the 92 also looks very stylish.

[Steve W8TOW]

what a beauty! That GPR-92 is a pretty thing....I had no idea the
bandwidth selections were diff between the 2 rx...interesting.

Well, my "found" GSB-1 needs a cabinet & a couple of knobs, but
the worse is the front panel needs silk-screening. It works perfectly tho
so other than cosmetics, no room to complain (plus the price was
reasonable!)

I wired mine with 2 speakers, one for the rx & a separate one for the
passband tuning unit....It would be nice if the rx had  the selector switch
on the front for using the adapter...and yes, I think it is telling me
to "box" the SX101A and use "her"...these rigs are like "yl's"
73