[Boatanchors] SX-24 rig thoughts - was Re: Companions to a BC-312 &a Halli SX-24

[Ian Wilson]

It isn't easy to make a VFO that is thermally and mechanically stable.
Mobile operation
makes things more challenging, since you will typically have less
separation between
VFO and heat sources, and movement/vibration is worse when mobile.

I would suggest doing both: use an oscillator with a switch that can
select between a
few crystal sockets, but also has a position that will allow it to
operate as a buffer/
multiplier from a VFO (perhaps external, to provide better thermal
isolation). That way,
you can get on the air easily, and experiment with different VFOs
until you find one
that suits.

The Vackar is a useful oscillator since it has more constant output
versus frequency
than a Colpitts. *Other things being equal*, a Vackar may provide
better isolation from
variable tube capacitances than some other oscillators. In any case,
choose a tube
with high gm and low input/feedback capacitances, and use a buffer stage between
it and the outside world.

73, ian K3IMW