----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Wednesday, October 24, 2012 9:08 AM
Subject: Re: [Drakelist] Neutralization
Steve:
IMHO, neutralizing the finals with the plate and screen
voltages removed is
the quickest way to neutralize and the easiest on the
finals. Several
older rigs have a final voltage disconnect plug to
accomplish this (e.g.
Central Electronics) and I always build in a similar
disconnect on my homebrew
transmitters.
Richard's cautions are well placed, you've got to remove
BOTH the plate and
screen supplies and both are at high voltage so caution is
advised (also,
make sure the HV caps have dissipated).
You'll need to measure the RF voltage at the output of the
final amp. The
easiest place to get this at the antenna connection and
the easiest way to
read it is with a scope (though most instructions will
have you construct a
low reading RF volt meter with a uA meter, diode and
capacitor). Just
remember that you will be tuning the final for maximum
RF, then neutralizing
for minimum RF.
73
Lee WB6SSW
My Kenwood TS-520S has a switch which disables the
screens for neutralization. That seems to shut the tubes off
well enough. I've tried neutralizing a Drake T4XB both by
disconnecting the screen only and by disconnecting both
screen and plate. Both work. I used a scope to find the
null. One could also use a receiver in the same way is
setting carrier null but that can be picked up with a
sampling loop while neutralizing really requires a direct
connection.
I think the reason special voltmeters are prescribed in
older literature was simply that suitable instruments were
not generally available, at least not outside of an
electronic lab. These days sensitive RF voltmeters and
scopes that to into the stratosphere are common so one need
not worry about building anything.
I will say that for high power amps a grid-dip meter
that can also work as a wavemeter/detector is helpful.
--
Richard Knoppow
Los Angeles
WB6KBL
[email protected]
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