On Friday, December 14, 2012 4:08:58 PM UTC-8, raypsi wrote:
On Tuesday, November 6, 2012 5:18:14 AM UTC-5, clifford wright wrote:

Has anyone else tried these circuits?



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.



According to the spec sheet curves:

The j310 gets turned off with a bias of 3.7vdc,

The datasheet for the J310 specifies a pinch-off voltage range
of -2.0 to -6.5V. Completely normal production variation may be
quite different than the spec sheet curve. So it sounds like
Clifford has J310s that have a relatively small pinch-off voltage,
perhaps even out of spec, and the ~2V drop of the diode chain is
biasing the FET off.

Data sheet for the Fairchild parts: http://www.fairchildsemi.com/ds/J3/J310.pdf

Dana K6JQ

I had the same problem and did not understood why.
I replaced the J310 with J309 and it works properly.
Regards