Dick,
You were one lucky guy with that DC accident! I somehow have avoided ugly
DC shocks (i am knocking on my desk with my hand as I type this), but have
had my share of 60 Hz touches, and plenty RF burns. Playing with a tesla
coil in high school was the source of some of them, however. Nasty jagged
waveforms. I suppose you could call it Nurdsville then.
I digress, maybe just to throw a topic besides parasites:
What got me interested in tube RF was the all glass 833. In the Gates
BC500T, there were a pair for modulator, and one for the RF I think. (it
was one huge box for 500 watts). Certain spots (advertisements) were
recorded with a lot of audio compression, on those endless loop broadcast
tape cartridges. Probably had a lot of distortion and clipping too. They
would make the class B modulators glow real orange in the center. Pretty
stuff. During dead air time (not supposed to be there, but crap happens),
the glow would diminish a bit. Of course, one could adjust the two bias
pots to get equal glow in both tubes (push pull) but that wasn't the right
way - use the milliameter instead. AM was so much fun, its interesting to
see a resurgence, although it isn't a robust mode for noisy 75 meters at
night, as I have noticed recently.
Gates (now Harris) made a transmitter called the Vanguard (Gary, W3AM, will
come out of the corner when I mention the Vanguard). It was shaped like a
low freezer, with a sloped front I think. It was grid modulated if I
remember correctly. Didn't sell too many, as high level plate modulation
was top dog. People wanted a tall transmitter, not a low table top unit.
Less floor space needed.
I worked part time as a broadcast engineer in college, for 3 stations one
time. Most of the work was during midnight to sunrise shift, when things
needed fixing without loosing commercial time. The Gates BC 1G was a
thousand watt version, with those same 833's. To neutralize it, you stuck a
screwdriver through the screened front, (could see everything inside when
it was running) and turned a big variable capacitor. My roomate was an
engineer also, and he and I found that the best way to neutralize it was to
send someone a mile away with their autoradio listening to our signal
leakage. When the plate voltage was off, but the filaments left on, the 807
rf driver would stay on. Tweaked the cap for a null in the radiated signal.
Simple, no test equipment required beyond a beer-drinking college student
sitting in his car doing what beer-drinking college students do in their
car. We never read about this technique in the manual.
73
John
K5PRO
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