December 16th 06, 11:48 PM
posted to rec.radio.amateur.boatanchors
|
|
external usenet poster
|
|
First recorded activity by RadioBanter: Oct 2006
Posts: 134
|
|
Tube-based 40M VFO
wrote in message
ups.com...
I've been having a lot of fun the past few weekends with my "new" Eico
720 and a couple of 40M crystals and a dipole strung between two trees.
But now I'm tired of QRM'ing the same frequencies all the time and want
to build a VFO. I've got some random variable capacitors, a couple of
nice dials, and would love to spend a weekend punching holes in a
chassis and putting something together.
I look in the 50's and 60's era handbooks and am a little confused. The
"SSB exciter" construction articles almost exclusively use a Vackar VFO
made out of a twin triode. Looks really straightforward and simple. But
the cookbook section inevitably shows pentodes in usually both grid-
and plate-tuned circuits, and then with extraordinary amounts of
buffering (say, a cathode follower AND a buffer amp).
I don't anticipate doing anything but 40M and some 20M in the near
future, and the Eico will double up to 14Mc just fine from 7Mc.
Will probably use a 0A2 type regulator in any event.
Am I giving up anything by just using the simple twin-triode Vackar?
The Eico 720's crystal oscillator combined with the crufty old crystals
I had isn't perfect to begin with, remember :-).
I'm guessing that all I need is 5V or so to drive to the Eico, correct
me if I'm wrong! With the crystal oscillator in it I almost always have
to back way way down on the grid drive so I'm guessing I've got some
extra oomph if I need it.
Tim.
always solid-state
http://www.minute-man.com/acatalog/A...adio_Kits.html
|