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

[Carl]

I believe the 12AT7 was the classic tube used used in the first (I dont have 
the reference handy so memory could be unstable and drifting (-; ) USA 
writeup with the second half the buffer. It makes an ideal circuit to feed a 
Pullen mixer also.

Carl
KM1H


----- Original Message ----- 
From: "Ian Wilson" <ianmwilson73 at gmail.com>
To: "Michael Tauson" <wh7hg.hi at gmail.com>
Cc: "Carl" <km1h at jeremy.mv.com>; <boatanchors at mailman.qth.net>; "arc5" 
<arc5 at mailman.qth.net>; <milsurplus at mailman.qth.net>
Sent: Wednesday, June 03, 2009 7:11 PM
Subject: Re: [Boatanchors] SX-24 rig thoughts - was Re: Companions to a 
BC-312 &a Halli SX-24


> 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