>>>One of the things that can cause an amp to oscillate is a low impedance
>>path >from the anode to ground.
>>
>>How? If it has a low impedance, you can't develop any volts between plate
>>and ground, so the amount of volts available to be fed back is less.
>
>? amen, Peter
I wanted to reply to this but I wanted time to think it through first.
The gird in a tube is essentially analogous to the gate in a FET and the Anode
is analgous to the Drain and Cathode the source. Now if I want to make an
oscillator with a FET I will feedback the output signal to the input. In other
words, I will connect a low impedance connection between the Drain and gate.
Now even though the gate may be grounded at DC, it is not necessarily so at RF.
The same thing happens in a tube. The feedback path is from the Anode to the
Grid. The grid is grounded, but we all know that it can be a few RF volts
above ground. So feedback can still occur. Now if I want to make an
oscillator, do I put a high impedance in the feedback path? No, I put a low
impedance. If voltage potential between the anode and grid of a tube or the
anode and ground was what caused oscillations, then and open circuit from anode
to ground would cause all sorts of havoc because the highest voltage potential
would be built up across an open circuit.
Oscillation develops from the feedback of signals. You want to eliminate that
feedback.
Perhaps this isn't worded completely technically correct and the technically
anal will, no doubt, correct me left and right. But think about it and you'll
see the general point I am making is correct.
73,
Jon
KE9NA
--------------------------------------------------------------------------
The Second Amendment is NOT about duck hunting!
Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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