[R-390] rebuilding RF transformers

[David Wise]

>>Any good mica

NPO* ceramic is fine too, and usually smaller,
cheaper, and easier to get.  Beware that in
some positions the cap has B+ across it; don't
use a 50V part there.

* 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.

Dave

> -----Original Message-----
> From: r-390-bounces at mailman.qth.net
> [mailto:r-390-bounces at mailman.qth.net]On Behalf Of
> Flowertime01 at wmconnect.com
> Sent: Sunday, September 13, 2009 8:42 AM
> To: r390 list
> Subject: Re: [R-390] rebuilding RF transformers
>
>
> Scott,
>
> There is nothing magic about the caps per say. They are very small
> packages. The variable caps are all the same. Then a fixed
> cap was added to get a
> mid range on the variable to make up the circuit. Over an hour or so,
> temperature in the cans of the RF deck are fairly stable, and
> the circuit is just
> band pass, so cap value drift with temperature is not the
> most critical
> function of the caps. Any good mica with in tuning range
> should work. You can go
> with some longer lead length and use a bit larger package.
>
[snip]