[Drake] ceramic trimmer capacitors
Garey Barrell
k4oah at mindspring.com
Sun Feb 3 14:47:10 EST 2008
Darryl -
The part is an Erie 557 trimmer, 5-25 pF, and is available from Surplus
Sales of Nebraska for about $7 each.
They're generally pretty reliable, _unless_ someone puts a pencil mark
on them to "reference" when twiddling on them. The graphite tends to
migrate and contaminate the cap. Not much to do to fix these. If
someone has just sprayed "contact cleaner" on them, they can be "really"
cleaned and restored to operation.
They CAN be cleaned and/or repaired, but it's not a trivial task. If
you look closely at the bottom, you'll see that the whole thing is held
together by a tiny "C" clip. If you remove that clip, the parts can be
separated and cleaned, then reassembled. There is a fixed ceramic disc
and another that rotates, with a rubber bushing between them.
"Cleaners" tend to gunk them up and stick them together so that they
rotate together. Not good.
If you decide to try the repair, remove the clip, dis-assemble the parts
(noting how they go together!), wash them in mild soapy water and then
dry thoroughly. Reassemble them _DRY_ and they'll work for another 30
years or so.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>
Darryl Trump wrote:
> I think I am having trouble with the crystal trimmer capacitor for the
> LO crystal oscillators in two of my three Drake rigs. I'm talking
> about the little white ceramic button about 5/8" in diameter that
> sticks up through the chassis and is adjustable. I think mine may be
> making intermitant connection, drifting, microphonic, and otherwise
> problematic.
>
> Question: Is this a common problem with sets of this age that use
> this type of capacitor?
>
> Is there a fix other than replacement? Can you clean and/or lubricate
> these things, and if so, does anybody have a favorite technique? I
> have cleaned and lubricated many a wafer switch or potentiometer, but
> never tangled with these trimmers before.
>
> Thanks,
>
> KB8BKU, Darryl
>
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