>
> Please give me an an example of a class A or AB linear PA that
> will go into a catastrophic failure induced by a oscillation when
> tickled with exactly the right transient, but will not oscillate under
> proper testing for stability.
>
...
I'm sorry, but I didn't say that I could do that. I do not know enough about
the dynamic behavior of tubes and tube amplifiers. When I learn more maybe I
will have something interesting to say about that, and maybe not.
I re-reiterate:
The claim was made by a Measures detractor that "the laws of physics" forbid
the existence of a non-self-starting oscillator. That claim is provably
false. That is all I say at this point. I'm not taking your bait on the rest
of Rich's alleged claims.
(By the way, I've been watching this argument on the list for a year or so.
I'm not exactly fresh meat here.)
>
>> I'll come up an example or two if you'd like.
>I'd like.
Here's an example: Build your favorite oscillator. Now put a latching relay
in the power supply leads and build a detector that will pick off some
signal from the feedback loop and trigger the relay when the voltage in the
loop exceeds, say, 1 volt. This circuit will sit on the bench and not
oscillate for years, but if you inject more than 1 volt of excitation into
the loop it will start going and keep going even if you remove the
excitation.
Artificial? Admittedly. But follow the logic:
1. This circuit obeys the laws of physics.
2. This circuit can be built and will behave as I described.
3. Therefore, the assertion that the laws of physics prohibit such behavior
is proven false by construction.
4. QED
The essential point is the inclusion of non-linearity (in this case, a
relay), either in the forward part of the loop or the feedback part.
Nonlinearity is certainly present in a class AB amplifier because the tube
is cut off for part of the RF cycle. (Remember, so-called "linear"
amplifiers are linear only at baseband, not at RF.) Thus, one can not reject
on general physical principles the type of oscillation described. I say
nothing about its likelihood in a practical amplifier. As I said before, I
don't know enough at this time to do so.
Respectfully submitted,
Carl WS7L
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