[HBR] Tuning Cap question???

[Walt Hutchens]

> What kind of voltages will this circuit generate?

I've never had a receiving-type circuit have voltage trouble in a
tuning cap.  They either work or they have a short -- or sometimes,
something more obscure, like a bad contact or open solder joint.

I wouldn't even bother with a voltage test.  If it passes an ohmmeter
test okay (rotate through entire range, push shaft gently in various
directions, you're good to go.

The disadvantage of a 140 pf/section cap is that you will have to
remove quite a few plates.  It'll work okay if the cap is
straight line capacitance -- rotor plates are half-circles with the
shaft at the center -- but otherwise you will get a pronounced
non-linearity in your tuning scale.

Also, a large capacitance unit with plates removed will not be as
stable as one designed for close to the desired capacitance.

Most 140 pf caps would be from BC or all band type receivers where the
tuning range was like 3:1 or so. These would NOT be straight line
capacitance types. If that's what you have, I'd look for another
tuning cap, closer to the specs for the HBR-series. They're not that
hard to find: Many old ham sets had them, ditto many FM-only
receivers.

The tuning cap is the heart of any receiver and once you've built a
set around it, you have a major project to swap it out for a better
one.  I'd keep looking.

Walt
KJ4KV