[Heathkit] SB 102 vs HW 101

[Alex]

RJ Mattson wrote:
> Early on (1976) my HW-101 kit developed a few kc jump in frequency at times. 
> I traced it to the mica compression trimmer on the vfo variable cap. After 
> replacing it with a glass piston trimmer it has worked flawlessly with no 
> jumps or warbles since 76.
> bob...w2ami

I ditto that one. My HW-101 that I restored also developed a drift 
problem, although it was a fast drift and it would jump back to where it 
started after a minute or so. I took the VFO out of the radio and tried 
to clean the variable cap with some compressed air, even though it clean 
as could be. As soon as the air hit the varicap, tiny bits of mica were 
flying all over. Apparently the mica insulation from the trimmers had 
deteriorated. Since I didn't have replacement parts I simply opened the 
caps and blew the remaining mica out and left the trimmers in that 
position, so that they essentially form air dielectric caps.

I expected the calibration to be way off, but found that only at a few 
points it's off by just 3 kHz, tops. I certainly can live with that. I 
have played with the idea of adding fixed value NPO caps, but the 
problem did not present enough of a problem to fix it. The drift of the 
VFO is minimal and well within specs.

I also replaced the grease on the Jackson drives and it tunes as smooth 
as silk again.

73,
--Alex KR1ST
http://www.kr1st.com