Sounds like you are adding POSITIVE feedback, not negative! Look up 'bridge
neutralization' in an ARRL or Bill Orr handbook. The grid side of the
neutralizing capacitor goes to the bottom of the grid tank circuit, which is
held above rf ground potential by a smaller than normal bypass capacitor. The
ratio between the bypass and the neutralizing capacitor determines the amount
of feedback.
You would do well to read the amplifier design chapter in one of those
handbooks; they have good discussions of neutralizing circuits and amplifier
stability in general.
Vic 4X6GP/K2VCO
> On Jul 26, 2015, at 7:48 PM, Roger <ai7rogerroger@gmail.com> wrote:
>
> Firstly, thanks all for the very positive responses I've received so far.
>
> I redid the neutralizing circuit and instead of a hard wired feed off the
> anode through a blocking cap to the neutralizing cap, I setup a single
> adjustable disc looking at an anode much like a gimmick wire would do and
> fed that to the grids. I'm questioning exactly where to apply this, though.
> At present it's going to the input side of the grid blocking cap.
>
> I pulled all the tubes and tested all the voltages and resistances at the
> sockets.
>
> I put the plate load resistor in place and with the Anritsu looking into
> the output I tuned the deck and was able to attain a 60db return loss and
> an absolute flat SWR.
>
> Then I hooked up the service monitor and using the tracking generator and
> spectrum analyzer, I was able to get a deep null at the op freq. It all
> looked perfect.
>
> But, and you knew this was coming, when I apply voltage and key the amp
> without excitation it instantly goes into runaway.
>
> ... and yes Bill, arcs and sparks and fireworks ensued. Gonna have to put a
> tag on the switch when I've got one installed.
>
> 73, Roger
> AI7RR
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