[Collins] 32S-1 Slug Rack Concerns

[Dr. Gerald N. Johnson, electrical engineer]

In my 32S1 manual, the slugs on the rack are never adjusted once they
are physically aligned with the tops of the IF cans with the rack tuning
set to 3.5 on the logging scale. They need only to physically track.
Each band has its own trimmer capacitors. If the slugs aren't lined up
with the tops of the coil forms at that setting, they are wrong. The
ceramic material of the slugs won't have changed permeability unless its
grumbled away or badly cracked. It is possible for some slugs to be
shorter than others by faulty replacement or by having crumbled from
mishandling. Even with the slugs in different positions, if the
capacitors for each band are set by the book it would work perfectly at
the frequency in each band where it was aligned, the only thing that odd
core position or composition should do is make it tune less well across
the band (and then it will track worse at WARC bands because they don't
have their own trimmers).

The slugs are probably mismatched in position because someone tried to
peak them AFTER twiddling the trimmer capacitors to random positions. In
the classic radio tracking days, one tuned the slugs at the low end of
the tuning range and the (single for the whole tuning range) trimmer
capacitor (per tuned circuit) at the high end. That technique isn't
necessary when there are individual trimmers for every band the radio is
designed for.

Unless the book was written in error (and I didn't especially like the
first 75S3B that came with my receiver, so I wrote the next edition)
alignment by the Collins book should result in a superbly working radio
(so long as there are no bad parts to upset performance).

Its possible that tolerances on some band may make a trimmer capacitor
peak at maximum or minimum C. Then the whole rack needs to be moved a
little to all that capacitor and all the trimmer capacitors for that
band to tune away from max or min. There should be no need to adjust a
slug, and indeed, if one compensates for that capacitor at the limit by
moving a slug, then ALL the bands already peaked on that tuned circuit
are no longer aligned. So move the whole rack to get away from a trimmer
capacitor at the limit.

Now if you get a condition where moving the rack runs one trimmer to max
and another to min on the same band, then you will have to move one slug
or both and then start over doing all bands ignoring that initial
setting of the slugs to match the coil tops.

I type fast but this has probably taken longer to type than it should
take to align the RF section of the transmitter.

73, Jerry, K0CQ, Technical Advisor to the CRA
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.