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[AMPS] info

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Subject: [AMPS] info
From: jtml@lanl.gov (John Lyles)
Date: Sun, 10 Jun 2001 09:46:10 -0600
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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