On Nov 4, 2004, at 12:14 PM, Dennis12Amplify@aol.com wrote:
Bill,
I have been reading your posts lately and want to commend you for
your
'sage' advice.
I also enjoy Rich's posts but lately he seems to be a bit cranky.
Maybe it's PMS?
I guess I would too if I kept having to fight the parasitic battle.
I kept thinking about the phase angle thing and realized that for a
grounded grid amp with .12pfd of plate to cathode capacitance to
oscillate at 1000
megacycles, the uhf circuit gain at that frequency would have to be
greater
than unity at a point where there was either no phase shift, or -/+
360 degrees
of phase shift between cathode and anode.
With the feedback impedance of 1326 ohms at -90 degrees voltage
dividing
with the input impedance of the tube (another vector but a low
impedance one),
It would take a significant amount of stage gain to cause
oscillations to
occur.
Good point, Dennis.
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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