I've monitored this reflector for the past several years; both Tom and Rich
have provided helpful information in response to my occasional queries.
My engineering background and professional experience are in digital design
and software engineering, not RF design. Disentangling their technical
arguments would take more effort than I care to spend. None of my amplifiers
(AL1200, SB220, SB201) has ever flash-banged, so I'd rather spend what free
time I have chasing DX or writing station automation software. But a
competent RF engineer should have little difficulty, particularly with the
tools available today:
1. select an appropriate circuit modeling program
2. construct a model of the tube in question, parametizing manufacturing
variances
3. construct a model of an amplifier circuit in question, parametizing
component tolerances
4. discover combinations of parameters, if any, under which VHF
oscillation occurs
5. construct models of alternative VHF oscillation-suppressing circuits,
and evaluate their effectiveness and side-effects
If the number of parameters is significant, step 4 might involve significant
computation to evaluate the combinations. Since the objective is to discover
combinations that produce VHF oscillation, one would start with a
coarse-grained search, and gradually reduce the granularity until an
oscillating combination is detected. Any such combination would then be
mapped in more detail by varying the parameters. Exploring the parameter
space for oscillations could be accelerated by dividing the search among
multiple computers and/or multiple investigators, just as the SETI-at-home
folks divide their search. Any reported "hit" could be evaluated and mapped
by everyone.
Clearly there are limits to the fidelity of software models. But if a model
oscillates with a realistic set of parameters, then oscillation is a
practical reality. And if no set of reasonable parameters can be found to
support oscillation, then for practical purposes the circuit being modeled
does not oscillate. Evaluating the effectiveness of suppressor circuits is a
similarly-objective excersize.
I suspect that neither combatant is truly interested in resolving the
underlying technical issue; doing so would terminate their righteous
justification for continuously elbowing and needling each other. It won't
stop until Rich publicly admits that he profits by selling unnecessary, if
not harmful, add-ons to ignorant amplifier owners, or until Tom admits that
he intentionally designed self-destructive amplifier circuits on behalf of
his quality-insensitive employers and hid this malfeasance by using the
influence of those employers to suppress Rich's whistle-blowing ARRL
handbook article. We'll be reverse-engineering humans from their genomes
before either of those things happens.
73,
Dave, AA6YQ
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