>
>On Thu, 14 May 1998 11:08:02 +0008 "George T. Daughters"
><gdaught6@leland.Stanford.EDU> writes:
>>
>>hi rich et al.,
>>
>>rich wrote:
>>
>>> If the cathode is not at RF-gnd potential, the resultant feedback
>>> decreases amplification.
>>
>>not always! it depends on the phase of the feedback that results.
>>in fact, it is very easy to build an oscillator that has the cathode
>>away from (RF) ground!
>>
>>but... rich and i both like the idea of putting a non-inductive
>>resistor in the cathode return to ground (in a grid driven tetrode)
>>to get some negative feedback at the desired operating frequencies;
>>it helps to stabilize the amp; it makes the amp harder to
>>overdrive, and it reduces the zero-signal plate dissipation.
>
>
>I agree with your comments in general George but with the following
>caveat.
>
>Rich wrote an article many years ago about modifying the NCL-2000 that
>way.
which magazine was this in?
>Since I was on the original design team and had 3 of them ( still
>do) I decided to try it. It was an absolute disaster above
>20M....oscillation city.
The use of cathode feedback R for the 8122 was not Rich's idea. It came
from the RCA technical specifications for the 8122. However, if one does
not use four low-L resistors with minimal lead lengths from the cathode
pins to chassis-gnd, all bets are off, Carl.
Rich...
R. L. Measures, 805-386-3734, AG6K
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