[R-390] rebuilding RF transformers

[Shoppa, Tim]

Dave writes:

> * To tell the truth, since the coils' inductance
> almost certainly increases with temperature, really
> the cap should have a negative tempco, like the
> ubiquitous N750.

Many slug-tuned coils end up having a small negative
Temperature coefficient which is matched well by a mica's
Slight positive temperature coefficient.

For air and toroid coils ceramic NPO's are often a better match.

N750 is a pretty strong tempco and typically would be used
As a  small part of the total tank capacitance.

Tim N3QE