> TU Rich! I am also thinking about trying neutralization on the amp,
> Maybe using a piece of solid copper from a piece of house romex wire (abt
> 14 or 12 gauge I guess?) and running it parallel to one of the tubes abt
> 1/2 inch away??, then to the filament choke and wrap abt 4/5 turns around
> it in the same direction that the choke was wound then to ground???
To neutralize the amp, the phase must be shifted 180 degrees.
That would require the winding oppose the choke winding.
Winding over the filament choke is also not a good idea. It is hard
to get correct mutual coupling. The AL-811H and AL-1200 use
separate broadband phase inverting transformers. For six meters,
you could use a small 43 mix core and a coaxial cable for the
inversion winding.
> that sound abt right? It "takes off" when I key it and turn the tune cap,
> then the grid skies and the plate turns red, even if I un-key it at that
> time it "takes off".
You may be in for problems, since the 572 is already unstable
enough at ten meters and lower. Is the grid well grounded?
You also, since the amp is a monoband amp, might be able to
stabilize it by series tuning the grid. The way to set that up is to
excite the cathode with a few volts of RF, and measured the RF at
the anode with a sensitive detector. Adjust the grid series tuning
capacitor for minimum feedthrough.
The same test setup works for neutralizing the stage, apply and
measure the RF through the entire input and output circuits, but
get the antenna relay out of the picture. There is a lot of coupling
around the relay, especially on VHF.
73, Tom W8JI
w8ji@contesting.com
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