Hi Roger,
First, is the circuit push pull/parallel or are all tubes in parallel?
If they are push pull you will need two neutralizing capacitors (cross
neutralization)
If all are in parallel the lead from the neutralization capacitor has to go
to the bottom of the grid coil with a capacitor to ground from that point.
The capacitor to ground gives a path to ground for the grid coil while
keeping it slightly above ground rf wise for the neutralizing path. This is
assuming you have a parallel tuned/link coupled grid circuit.
The neutralizing signal has to be out of phase with the grid.
You should also be using the grid bypass rings on the tubes. These are the
rings with the fingers with the bypass capacitor built in.
You should always have a 50 ohm load on the output and one on the input too
if not connected to the exciter.
73
Gary K4FMX
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Roger
> Sent: Sunday, July 26, 2015 11:49 AM
> To: amps@contesting.com
> Subject: [Amps] Follow-up...re: Time to ask for help.
>
> 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
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|