----- Original Message -----
From: "Steve" <[email protected]>
To: <[email protected]>
Sent: Tuesday, October 23, 2012 6:17 PM
Subject: [Drakelist] Neutralization
I have a Drake T4 that needs neutralization . I have tried
the approach given in the manual and while it seems to work
I thought I might use this as an opportunity to learn how
to do what is called a Cold Tube neutralization where you
do not apply High Voltage to the plate. Seems that you can
Neutralize the tube with only filament voltage, bias and
screen voltages applied. Has anyone done this and if so
what is the preferred method of doing it.
Steve NU0P
I think this is a confusion of the traditional method
of neutralizing where the tube is fed with FR but with no
plate or screen voltage. You can remove the screen voltage
and neutralize with plate connected or disconnect both but
if you remove plate voltage without also removing screen
voltage the tube will burn up.
The idea is to set up the amplifier for normal drive
and tuning and then disconnect the HV. Then measure the feed
through of RF on the plate side and adjust the neutralizing
capacitor for minimum feed through The neutralizing
capacitor forms a bridge circuit with the interelectrode
capacitance of the tube and is adjusted to balance to
prevent positive feedback from output to input with
consequent oscillation.
Some care is necessary because you can't disable the HV
supply in the small Drake transmitters so you must
disconnect it at the feed-through caps for the tubes. That
is dangerous both because its a shock hazard and because of
the danger of accidental shorting of the supply.
The handbook method is fussy but works.
--
Richard Knoppow
Los Angeles
WB6KBL
[email protected]
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