Heath VF-! VFO stabilizing
 

Any articles or experience on taming drift in the Heath VF-1 VFO?

Peter

" Uncle Peter" ) writes:
Any articles or experience on taming drift in the Heath VF-1 VFO?

Peter



QST for November 1972 (I'm pretty sure I got that right). But you won't
like it, because it's about pulling the tube, and putting an FET in there.

That was right when the rules changed so the US Novice license no long
required crystal control. So someone decided it was a good time to
transistorize the old VFO.

Michael VE2BVW

" Uncle Peter" wrote:
Any articles or experience on taming drift in the Heath VF-1 VFO?

I got mine to be pretty stable. First I removed that big heat producing dropping
resistor (was it a 10K 5 W? it's been a few years) from under the chassis and
away from those heat sensitive frequency determining parts. Then I added a few
holes in the upper case to help remove more tube heat. Finally I got a small
filament transformer and ran the VFO filaments 24/7 which really helped with
warmup drift, which as I recall sometimes went on slowly for up to an hour. The
always-on didn't seem to hurt the tube life as I recall, but heck I had a bin
full of those 6AU6s anyway so it wasn't a problem... ;)

The note on the QST article for the FET conversion is a good one to
look into. I've done the conversion on several VF-1 VFOs and the
result is spectacular. Last one I did cost just under $25 to buy all
the parts new. However, I do away with the authors scheme for
dropping the supply voltage, from the transmitter, and added an
internal 20 V DC supply to run the thing. Works great and you can
then use it with any rig you desire.

Bob WB8CAC
http://www.qsl.net/wb8cac

The one I currently have was very unstable until I found and corrected the
problem - the low frequency (1750-2000 kc) coil for the tank circuit had
several loose turns on the grid end, where the coil dope had dried out.
Tightening up the wrap of the coil and sealing the turns with some epoxy has
resulted in a very stable oscillator. Its still kind of sensitive to
mechanical shock, so don't bang on it, but once it's set, it stays!

Chris Bowne, AJ1G
Stonington,CT