[R-390] rebuilding RF transformers

[David Wise]

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.

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

Dave Wise

> -----Original Message-----
> From: Shoppa, Tim [mailto:tshoppa at wmata.com]
> Sent: Tuesday, September 15, 2009 11:48 AM
> To: David Wise; r390 list
> Subject: RE: [R-390] rebuilding RF transformers
>
>
> 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
>
>