[Collins] Ailing KWM-2

[Dr. Gerald N. Johnson, electrical engineer]

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.
Reproduction by permission only.