Thanks to Skipp for the Dayton Amp Vendors pics. Yes, they do all
look sort of similar. Remember when they didn't? Thunderbolts,
Warriors, Desk kW, SB220, 30L? Tetrodes, Triodes, all glass?
---------------
I wanted to (and forgot Friday) comment on the note by Jon about use
of ATC ceramic capacitors instead of Micas.
3 years ago I tried to carefully bypass the filament leads (Common
mode and differential mode) for the couple hundred kW 2800 KHz
amplifier I built for work. Mica blocks could be made to work, but
they went inductive so quickly, just above where I ran them. Not too
bad, but I tried ATC100E series ceramic chips with the big fat
silvered ribbon leads. They were great. I used 10 to 12 of them
around the socket, very simple to use with just sissors and a hole
punch for a screw. I used the biggest i could get, 2200 pf, good for
2 kV or so. I measured the bypassing with the impedance meter (Hp
4903?) for several decades above my frequency of operation. They did
the trick. I ended up using 3 mica blocks, to ground from one side,
and the 10-12 ATCs across the filament. This hybrid bypass capacitor
did the best at keeping RF off the filament and lowering the
cathode/ground inductance for the tetrode. Somewhere I have a photo
of the socket with the finished bypass, if i could post it somewhere.
For a 200 MHz Burle 4616 tetrode, we also use a 390 pF version of the
same, one across the 'elevated' filament lead to ground, and one
across the screen to ground. Very closely mounted at the tube
'stems'. It worked so well that we recommended it to the manufacturer
for their test set, as they had a lot of RF leaking out of this
otherwise well shielded metal/ceramic tube. The tube has internal
mica bypasses but some RF still runs up and out of the stems at
VHF/UHF.
73
John
K5PRO
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