Re: Transistors

On a sunny day (Mon, 19 Nov 2007 08:42:09 -0800 (PST)) it happened Winfield
Hill <hill@xxxxxxxxxxx> wrote in
<869fdae0-823c-4d47-b987-bab35c0b9c4b@xxxxxxxxxxxxxxxxxxxxxxxxxxx>:
This is with lower emitter io resistors:
ftp://panteltje.com/pub/amp1_ac2.jpg

Small-signal spice tests (frequency sweeps) of power-
amplifier circuits like that, at high-frequencies,
are close to meaningless - useful for no-signal loop
stability perhaps, but certainly not for evaluating
how an amplifier can do at delivering power at high
frequencies. You can try transient full-power tests
with spice, but I'd want to verify the component
models on the bench before giving it much credence.
And of course, when the failure mode is thermal, and
your spice model isn't set up to handle self-heating,
well... What you can do with spice, after you've got
models you can trust, is to evaluate the continuing
emitter current in a class AB transistor after it's
supposed to have gone off or nearly off each cycle.
Doing this will help teach you what's badly wrong
with that circuit for high-frequency high-power use.

OK, you do have a point, and I have not build this one
with these transistors (that would be the real test,
I trust spice more then in the past, but reality rules),
but this begs the question to *you*:
How would you do it?
You mentioned class A, and this was an attempt to go towards
class A from my side (decreasing the emittor resistors
decreases the phase shift).
I am curious how you would solve the 20V pp 10MHz say 50 Ohm
load and open drive?
.