w5kcm ) writes:
I am building a crystal tester and the circuit calls for two 220pf
caps in the oscillator. I didnt have any of these caps in the junque
box so I thought about making a couple gimmick caps. I understand this
is done by twisting some insulated wires together. Is there some guide
to use that will give you an approximate value? In other words, if I
have twisted some #26 enameled wire together does 1" equal some pf
value? Any info you may have on this will be appreciated.
w5kcm

"Gimmick capacitors" are when you need only the tiniest amount of
coupling. They are just a step up from placing a wire near another one
(such as when there is enough stray coupling from a bfo to a diode
detector for a sufficient beat). They are likely sub-pF, and if
they are any higher then a couple of picofarad. In other words, the
value needed is so low that you can get by with a pair of twisted wires.
If you need something substantial, then you use a real capacitor.

Another advantage of a "gimmick capacitor" is that it's somewhat variable,
sicne you can adjust the twist and even trim the wires to get a different
capacitance.

Michael VE2BVW