Gosh . . . after the gazillion notes and high-powered discussion, what I
ended up doing seems absurdly anticlimatic.
I tried Gene's idea as described below. Loosened the nut at the rear of
the cap, but to no avail.
Then I put a tiny drop of Hoppe's 9 high viscosity lubricating oil (gun
oil) on the rear shaft. That seems to have done the trick. The rotor
turns much easier and about what I'd call normal.
At the risk of spawning another interesting thread of emails, I'd like
to ask the group two follow up questions related to the same air
variable capacitor.
I had access to a Sencore LC-102 capacitor-inductor analyzer today and
used it to measure the capacitance and leakage of the Johnson 153-6-1.
Admittedly, the tech whose shop I borrowed did not know when the LC-102
was last calibrated, nor did I have a "standard" capacitor to use as a
benchmark. The Johnson 153-6-1 measured 58pf min and 538pf max
capacitance. The Cardwell web site lists this model of Johnson capacitor
as 36pf min and 496pf max capacitance values. Wonder why the values I
measured are so notably higher than the spec? Non-metallic work bench
and I self-calibrated the LC-102 prior to making the measurements.
The LC-102 can also generate as much as a thousand volts for measurement
of leakage current. So I put 1000VDC (the capacitor is rated for 3500
volts) across the air variable and measured leakage current thru it. The
value of leakage current varied ranged between 1 and 2 microamps as I
turned the rotor. Leakage current seemed to be slowly increasing as
time passed. What is typical leakage current for this type of capacitor?
What is the leakage path? Can the leadage be reduced/eliminated? Or,
more to the point, should I be concerned with this level of leakage
current? As a comparison, I had three other air variables (including two
big transmitting air variables of the type used in Johnson KW
Matchboxes) that measured zero leakage under the same test conditions.
Advice?
Thanks everyone for being so helpful.
Steve K8JQ
-------- Original Message --------
Subject: Re: [TowerTalk] Lubricating air variable capacitors
Date: Sun, 02 Oct 2005 15:33:18 +0000
From: ersmar@comcast.net
To: Steve <steveac@charter.net>, towertalk@contesting.com
Steve:
These large variable caps have nuts on the front and back panels
to hold the whole thing together. I had trouble turning the shaft one
one surplus cap at my station so I loosened the nut at the rear of the
assembly a bit. Worked like a charm.
You might try that before lubing the cap.
73 de
Gene Smar AD3F
> I have recently acquired a used Johnson 153-6-1 air variable capacitor
> for use in an antenna tuner. Looks to be in pretty good condition, but
> it does not turn as freely as one would expect.
>
> Is it likely that lubrication would free it up some?
>
> Is it OK to lubricate this type of capacitor? With what? And where?
>
> Thanks.
>
> Steve K8JQ
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
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>
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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