[Amps] Antenna Tuner Overheating

[Vic K2VCO]

Jim Brown wrote:

> Any ideas what's going on?  The fixed capacitors in the tuner high 
> voltage types, but with significant temperature coefficient. Are they 
> heating and changing value?  

I'm not familiar with these tuners, but if they use the doorknob 
capacitors with N750 temp. coefficients, I am sure that is the problem.

I tried to use these capacitors at only 800 watts in a homebrew 80/160m 
tuner and the SWR would start to rise almost as soon as I pressed the 
key.  I replaced them with large bathtub micas and the problem went away.

I also had a trap in my inverted L which used four parallel 68 pf 5 KV 
doorknobs.  At 1.3 KW, boom!  I replaced them with another large bathtub 
mica, which has worked fine ever since.  I think the doorknobs are for 
bypass service only.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco