Howdy,

Heh! I didn't look at the url for that schematic, it's an SW3!
I love National Radio gear. I had two HRO-500's, sold one, and
there's an FRR-59 in my basment. I regret having sold my pristine
RBL receiver which beat the pants off either the HRO-500 with LF10
or the Racal RAL7 with RA237 for LF/VLF work. My highschool's club
had an NCX-1000 which I lusted after... er, but only in my heart.

But back to the SW3. I recall padder capacitors mounted on the
top of the RF stage coil former. I don't know the value of the
dual gang tuning capacitor but armed with that, Wheeler's formula
and these sites, you could calculate the effect of the grid circuit
to some extent.

http://www.io.com/~nielw/sw3coils.htm
http://www.antiqueradios.org/gazette/swevol.htm


73,
Grumpy