[Collins] Mods for 75S receivers.

[Gerald]

On Thu, 2005-04-14 at 06:33 -0500, cory wrote:
> What's the link to the site with the crystal boards for 75S-1s?
> 
> I'd like to set up by 75S-1 for general coverage listening.

What I did for my 75S-3B decades ago was to unhook about 30 pf of
capacitors in the oscillator circuit and run miniature coax (its
capacitance replacing that of the fixed capacitors) up to a spst toggle
switch and crystal socket mounted with the screw on top the coil rack
drive mechanism. Makes changing the crystal a lot easier than digging
down to the crystal socket. I considered hanging a box outboard with a
30 position rotary switch but never completed it.
> 
> Also, is there a source for CW filters for the 75S-1?  I believe
> that I have to add a CW BFO crystal too and these come as a set?

You do need both filter and crystal. When I bought them for my dad's
75S-2 I recall getting them separately though they came taped together.
The filters can be had occasionally, check also with International
Radio. The S-1 and 2 took a round wire in filter under the chassis. It
was fairly large and round. I'm sure the part number for both crystal
and filter is in the manual. Today a BFO crystal probably can be had
(for a king's ransom) from Surplus Sales of Nebraska or International
Crystal Company at Oklahoma City.


> 
> Any other must have, mods or enhancements for the 75S-1?  
> 
> Also, what's a good way to polish the knobs?  Mine are looking
> dull.
Use should polish the knobs. I have a 51J that was covered with pipe
smoke tar and the cleaner that took it off dulled the knobs. I can
polish them with a cotton wheel and white rouge. Mount them on a piece
of shaft to give a handle to keep from polishing fingers too much.

> 
> de ah6gi/4 caretaker of 75S-1 serial number 55.

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer