[Amps] LF oscillation caused by defective plate choke?

[N1BUG]

On 10/08/2013 12:17 PM, Fuqua, Bill L wrote:
> There can either be a feedback path that causes the problem due
> to the fact that by-pass capacitors are chosen to bypass HF RF
> not low frequencies

That is what worries me. I wonder it it was on the edge of 
instability all along until a minor change in the plate choke pushed 
it over the edge. I wonder if I should think about upgrading the 
by-pass capacitors? The by-pass at the cold end of the plate choke 
is only 1000 pF which has always worried me a little. Some others 
are the same or not much better.

I neglected to mention this is cathode driven, swamped with a 
resistor. Gain is 13 dB. The grid is at RF ground (6000 pF) and 
screen clamped to the chassis.

> The difference in the chokes is likely to be their Q. If the
> choke had lower Q the amplifier would be less likely to
> oscillate.

That makes sense.

73,
Paul