On Tue, 6 Nov 2012 02:18:14 -0800 (PST), clifford wright
wrote:

Has anyone else tried these circuits?

No, but I saw that in theory they might work.

I have built 2 examples, a 9 MHZ AGC controlled amplifier and a 20 dB wideband amp for a noise cancelling system.
BIG problems! The diode string in the source of the FET always biases the J310 OFF.
Result, no gain or a loss!!!

The spread in FETs is rather high so you might have had the bad luck that the
ones you used have a cut-off Vgs lower than ~ 1.8V. One issue is strange though:
maximum gain occurs not at the limit of V(AGC) of 4V but at a higher voltage.
At 8V at the base, one stage (J310 +2N3409) provides for some 16 dB (voltage
gain) then but about 10 dB of it is due to transformation from 50 to 2200 ohm at
the input LC.

It took me an hour or two to twig what was going on. The trouble is that I cannot see how it can possibly work when the gate is referenced to ground. It is equivalent biasing off a valve!
Not only that, but the AGC circuit published at the same time had extreme instability in the front end of the AGC amplifier. I am a VERY experienced electronics person (60 years) and was unable to find any obvious reason for this.

It could be useful to try the circuit with a FET with much higher cut-off gate
voltage. An example is BF246C and BF247C. It should work with the diodes in
series with the source resistor.

SO Now I have actually began to lose faith in one of my favourite engineers.
Or, have I done something really stupid in my old age.
FYI the circuits were built "dead bug" style with extensive shielding and full decoupling.

I wonder why you didn't try to get an oldie like the Plessey SL312. Look it up,
and see that it's perfect for the job - it provides some 30 dB gain without an
input up-transformation and with a larger AGC range.

Regards,
Jan