[Amps] Instability update, Apr 16

[Bill Turner]

ORIGINAL MESSAGE (may be snipped): 
On Tue, 16 Apr 2013 22:23:52 -0400, N1BUG wrote:

>No change in LF parasitic. 

REPLY: 

Your tube may be oscillating as an old fashioned TPTG (Tuned Plate Tuned
Grid) oscillator.  

Something in the plate circuit is present a large impedance at LF. Do you
have a relatively large choke such as a 2.5 mHy or so in the plate lead as a
filter? If so, try removing it. 

You want the impedance, measured from the plate of the tube back to the
output of the power supply, to be very low impedance at LF. If the impedance
is low enough, the tube will not oscillate. The same statement holds true
for the grid-cathode circuit. 

Bill, W6WRT