[AMPS] Two Questions

[W0YR@aol.com]

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
  

--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com