Tube-based 40M VFO
 

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.

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

Tube-based 40M VFO
 

wrote:
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).

snip

Hi,

You might look at the matching Eico 722 VFO manual on BAMA:
ftp://bama.sbc.edu/downloads/eico/722/


73,
Ed Knobloch

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.


I always like John Seboldt's K0JD's approach to homebrew / build a VFO.
He used a military surplus T-368
http://www.seboldt.net/k0jd/analogvfo.html
http://www.seboldt.net/k0jd/t368vfo.html

Other VFO's
http://www.seboldt.net/k0jd/othervfo.html

Tube-based 40M VFO
 

Tube-based 40M VFO