[Racal] RA6830-516 Spin Knob

[Dallas Lankford]

I have never been satisfied with the light weight plastic tuning knobs =
of the RA6830 receivers.  They make fast band scanning virtually =
impossible.  Weighting the knob had been tried by a previous owner of my =
JD, but that was not satisfactory either.  I looked around for spin =
knobs (with cranks), but never found anything I liked.  So I decided to =
make my own.=20

For the knob I used an Alcoswitch black anodized machined aluminum 1.75" =
diameter knob, Mouser 506-KN1751BS1/4 (about $18).  This is a very =
nicely finished knob, with finger dimple, which has also been sold on =
Ebay recently for about half the above price.  The dimple is somewhat =
small (and I have small hands and fingers), and should be larger for =
effective spin tuning with it.  I drilled a hole through the center of =
the dimple (36 gauge), all the way through, and tapped it with a 6-32 =
tap, all the way through.  I put a 1" long 6-32 round head brass machine =
screw wrapped in rubber (or other suitable material to protect its =
threads) into the chuck of my hand drill, and ground off the side of the =
head to slightly less than 0.25" with a small file while spinning the =
head.  The resulting sharp edges were beveled with the file.  The round =
head was refinished to a flat head.  A 1/4" OD 1/2" long nickel plated =
brass round Keystone spacer, Mouser 534-1457C, was slipped over the =
screw, and the screw was brought down flush, and backed off about 1/2 =
turn.  A small Alcoswitch black anodized knob for a 1/4" shaft, Mouser =
506-KN500B-1/4, was fitted over the spacer and checked for fit.  =
Additional adjustments were made as necessary, and the fit checked again =
as necessary.  Then the screw was backed out several turns, a liberal =
dab of 5 minute clear epoxy was put in the screw hole from the =
rear,screwed the screw flush again, and backed it out about again 1/2 =
turn again.  Another liberal dab of epoxy was put over the screw hole on =
the back to make a nice dome of epoxy about 1/4" or so in diameter.  Let =
the epoxy dry hard for about an hour, and it is ready to use.  The brass =
screw can probably be removed if necessary by removing some of the epoxy =
at the rear and using a lot of force with a screw driver.  The head of =
the screw will probably be burred.  An the screw hole will have to be =
tapped out again to remove epoxy residue.

I also replaced the audio gain and IF gain knobs with black anodized =
Alcoswitch knobs, Mouser 506-KN500B1/8 (1/8" shaft).

After all this effort, you can imagine my dismay when I noticed that =
microprocessor noise became audible when I touched the main tuning knob =
as I tuned through the 19 meter band while checking out my new spin =
knob.  Apparently this is why Racal used plastic tuning knobs on 6830's. =
 Elimination of the noise due to the spin knob will be discussed in =
another posting.

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