It took awhile to build this project, once I finally decided to use the
833C tubes instead of the NOS Russian GS-35Bs I have. Since I built it
during a period when I had little extra money to spend, I spent more
time figuring out how to build the amp with parts that I already had
laying around here than actual construction time.
But I think that made the project more satisfying. I know I wouldn't
have felt the deep satisfaction I do when I use this amp had I been
able to afford a commercially built linear.
I don't know of anyone who has ever built an 833 linear amplifier
similar to this one.
I was inspired to use 833s from a construction article in the 1980 ARRL Handbook
but I had to make a lot of changes from that article to make it work
right. The 50 ohm swamping resistor just didn't work, for one thing,
plus the plate Z was much different because I used two 833Cs in
There were a few things that I wish I had done differently, but in the
end, I was really surprised at just how well this amplifier works. No
trace of instability or any blower noise (or smoke).
If you build an amp, for heaven's sake don't use the same cheap meters
that I did. They are cheap Shurite
meters with no damping, and they jump all over the place, making it
almost impossible read the exact grid or plate current. They would be
monitoring a constant current, but NOT a varying one. They are almost
tolerable amplifying a RTTY or AM signal, but in either SSB or CW those
meters jump from minimum to
maximum scale like a couple of windshield wipers gone totally berserk.
I use the Westinghouse plate current meter on the panel below the amp
(drilled by another ham before I got it.) The Shurite meters are better
than nothing, that's about all I can say.
Surprisingly, the Dow-Key relays (which I already had from a previous
144 MHz amp project) switch fast enough to show power output even when
sending a single dit at 70 WPM. But fast vacuum relays would certainly
be better, especially if they were acoustically isolated from the metal
chassis. Maybe someday. The external contacts on those relays are
connected in series, and jumper the cathode-to-ground resistor to
energize the tubes.
I never drew any schematics except the bias supply and a few control
circuits, etc. Maybe I'll draw one and post it here someday. But you
can figure out most of what I did from the photos
should you want to build one similar to this one.
See you on 160 meters. :-)