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[TowerTalk] [Fwd: Re: Lubricating air variable capacitors]

To: towertalk@contesting.com
Subject: [TowerTalk] [Fwd: Re: Lubricating air variable capacitors]
From: Steve <steveac@charter.net>
Date: Mon, 03 Oct 2005 19:32:39 -0400
List-post: <mailto:towertalk@contesting.com>
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 
> Weather 
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> and ask for Sherman, W2FLA.
> 
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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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