[R-390] rebuilding RF transformers

[Shoppa, Tim]

> Sorry for the misinformation!  Does that net negative tempco
> come from the slug?  Because the coil form always
> expands, giving air-core coils a positive tempco.

The reason that so many handbooks for so many
Years pushed silver micas so much, is that the tank
Inductance in ham gear VFO's was usually a slug tuned coil.

I think the amidon tables and the ARRL handbook have some tempcos for typical
Modern iron powder toroids.

> Do you have a good source for compact small-value medium-voltage micas?

Mouser, digikey have Cornell Dubilier's. I think Allied has a wider selection
(more oddball values). For RF deck purposes I'm sure modern ceramic NP0's will do
Just as well. If you're building or rebuilding a VFO, you have to be very
Critical with respect to tempcos.

Tim.