TOM wrote:
Mostly better design and charericterization. The VFO's designs
were tested for temperature drift, and temperature-compensating
capacitors were made part of the design. I think a few radio VFO's
were actually tweaked as part of the unit test for temperature stability,
but not sure. It would have been expensive.

The capacitors are coded:

N - for negative temperature coefficient
P - for positive temperature coefficient
NP0 - for no temperature coefficient.


I used a 10pF ceramic temperature stability not marked
across the LC tank. Mounted it directly under the 12BE6
tube so it would be warmed by that tube, like a hen on
eggs. One lead connecting to a center ground peg of the
tube socket, and the other a wire jumper to the top of the
LO tank. Keeps the radio stable at 1520 from a cold start
to warm. Only thing is now the radio top ends at about
1540. Also reasonably stable at 1160, and 660.