[Collins] Ailing KWM-2

[Herzog]

A fix for compression mica's is to exclude the air by using silicone oil.
When I was working on a design for some military gear, we were enchanted by 
the price and hence savings possible.
A 200 volts breakdown could be raised to 600 volts.  However these were 
fixed caps, and the silicone oil was in a bowl, and the caps then dropped 
in, and placed in a vacuum bell-jar pulled about a half hour until the air 
bubbles ceased.

    This is too iffy for a product, but the idea of silicone oil could save 
the marginal Collins design.

I suggest that You MUST clean out the black stuff from previous arcs first, 
loosen the screw , insert oil liberally, close cap some, and allow for the 
dripping. Over tightening mite squeeze out too much oil.
K 2 L B

At 03:03 PM 12/14/02, Dr. Gerald N. Johnson, electrical engineer wrote:
>The compression mica loading trimmers are the known weakest parts of the
>PAT tank circuits. They don't have proper controls of dielectric using
>mixed mica sheets (at best a little nonuniform, at worst with conductive
>inclusions) and air. When the thickness of air and mica are about the
>same, the high dielectric constant of the mica forces most of the
>voltage drop across the air which can then arc and the heat from that
>arc can blow holes in the mica. These capacitors were never intended for
>handling RF power. Moisture can lead to even more problems. They are
>compact but overworked.
>
>And when the loading capacitor is shorted, the effective value of the
>tuning capacitor is increased hinted at by the higher frequency resonant
>position.
>
>73, Jerry, K0CQ
>--
>Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
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