Hi Bill,
I have redone two old B&W tanks in which the neoprene spacer bars were
"cooked" because of high circulating current.
I used some teflon rods (you could also use bakelite strips). The rods were
of about 3/4" diameter. I first very carefully noted the spacing of the
turns for each section. Then, I used a drill bit of the same size as the
various conductors for each different section. Using my drill press and a
drilling-vice, I drilled the holes so the wires/tubing would "snap" into the
rod. Since the Teflon is relatively expensive, I would try this first using
a piece of dowel rod to get the feel of how to do it. Of course you should
not use the dowel; just use it to see how to go about drilling the teflon.
On the subject of neutralization, you cannot neutralize a triode amplifier by
dealing ONLY with the grid circuit. Remember that it is the feed-back
through the grid to plate capacity of a triode that causes the tube to
oscillate as a tuned-grid tuned-plate oscillator. You have take some of the
r.f. current from the output or input circuit of the amplifier and introduce
it into the other circuit. For complete neutralization the two currents (the
one flowing through the normal grid-plate capacity and that flowing through
the neutralizing capacitor) must be of the same amplitude and opposite in
phase. The value of the grid-plate capacitance and that of the neutralizing
capacitor will be approximately, but not exactly equal and the use of a small
value variable capacitor allows it to be "tweaked" into range.
There are circuits in which the neutralizing voltage is obtained from a
balanced grid tank and fed to the plate through the Cn. These are called
"grid-neutralized" circuits. In either case the neutralizing circuit must
involve both the plate and grid regardless of where the neutralizing voltage
is obtained. Grid neutralizing is less satisfactory than the plate method.
Either method requires a Cn of high voltage rating and of small capacity.
Hope this is helpful.
73,
Mike
W0YR
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