Hi Jack,

Grid stoppers: A low value resistor (100 ohms) attached directly
between G2 and the screen supply to reduce the incidental Q of
circuit. Same applies to G1.

APC - Anti Parasitic Choke. A few turns (10 ?) of 22AWG enameled
copper wire around the out side of and terminated with a 10 ohm 1W
resistor. If the AMP becomes unstable at VHF, the reactance of the
small inductor will increase and the 10 ohm resistor will dampen the
mayhem.

See http://www.somis.org/Oct88qst.html

From your photo, I think you may need to considerably reduce the
length of your wiring before you should tackle stability issues. Anode
circuits should be above chassis, grid below chassis and never the
twain should intertwine. It looks like you make have lots of inductive
coupling between the two at the moment (long wires etc.) which may
well be the cause of your problems.

Also take care of proper de-coupling - directly to chassis with
minimum lead lengths (1 inch max ?).

Get a 1960s copy of the ARRL handbook and read up on HF amplifier
construction techniques. There has been plenty written.

Regards,

Mark.


On May 24, 1:23 am, Jack Schmidling wrote:
MarkAren wrote:
Hi Jack,

Have you tried removing drive to the PA and looked for output RF ?

Roger. Just pegs the meter with no output.

Grid stoppers in place ?

What's a grid stopper?

APC in the PA anode ?

What's APC?



Any chance of a photo to look at construction techniques ?

Sure. http://schmidling.com/807a.jpg

Needs a little cleaning up. Note the careful placement of the grid coil
at right angles to the final and with the Masonite panel between for
good shielding.

js

--
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MarkAren wrote:
Hi Jack,

-- snip --

APC - Anti Parasitic Choke. A few turns (10 ?) of 22AWG enameled
copper wire around the out side of and terminated with a 10 ohm 1W
resistor. If the AMP becomes unstable at VHF, the reactance of the
small inductor will increase and the 10 ohm resistor will dampen the
mayhem.

See http://www.somis.org/Oct88qst.html

-- snip again --

I have read that these are better built with a bit of resistance wire,
because the inductor is reputed to sometimes work too well.

I dunno the details though -- all my work ends up being QRP, so I
haven't had occasion to make such a beastie.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html