[R-390] Re: [R390] R390A trimmers

[Graham Baxter]

I did manage to get all the trimmers working again. The problem was
that the lower ceramic disk was no longer anchored by the rubber to
the paxolin. I dismantled the trimmers and washed them in alcohol. I
also polished the silvering where the spring contact will press. I was
then able to reassemble them using a spot of cyanoacrylate adhesive
either side of the rubber. This has worked well. One of the trimmers
had a broken ceramic disk. I reassembled this with cyanoacrylate glue.
I bridged the crack on the silvered part by soldering a piece of
copper foil across it. I would have liked to use conductive silver
paint but I didn't have any. This trimmer at least is scheduled for
replacement when I have spares.

I found my 9MHz crystal was poor. I tried a cheap HC47 wired crystal,
just poking the wires in the holder, and it worked fine on 7, 15 and
24 MHz. So I opened the old crystal, removed the blank and replaced it
with the entire new crystal. I replaced the can and it looks great.
Interestingly there was a tiny fracture at the edge of the old blank.

R390A s are not so common in the UK. I am fortunate to have a couple
of friends who are enthusiasts. As well as two EACs I also have a
Racal 1772.  It is good but not as good as an on-song R390A.


Thanks for your interest

Graham
G8OAD