> > You are making mountains out of what turn out to be mole-hills. It's
> > pretty easy to find the extremes in phase shift and loss at several
> > points, and determine if oscillation is possible.
>
> If they were indeed molehills, the questions surrounding VHF oscillation
> and suppressor effectiveness would have been resolved long ago.
They are resolved in many people's minds. There seems to be only
one person behind claims parasitics are the root of all evil.
Most everyone else with engineering experience on vacuum tube
PA's and a science/physics/engineering background seem to
agree.
> > I think maybe the mental picture you have of the system is
> > incorrect, perhaps you are assuming wild gyrations on multiple
> > frequencies. Multiple complex resonances and feedback paths are
> > typical for "unclean" layouts, like a breadboard wooden chassis
> > PA with point to point wiring, but not in modern PA's with decent
> > construction.
>
> Words like "wild", "unclean" and "decent" are subjective, and thus not
> conducive to proving anything.
If I had twenty years, I could write a book on what makes an
"unclean" layout using scientific terms. As it is, you'll just have to
consider poor ground, long leads, and components that exhibit
changing characteristics due to internal construction errors as part
of "unclean" layouts.
I gave the example of breadboard construction. Do you know what
that is, and what it looks like?
Modeling eliminates the need for imprecise
> formulations in natural language. One describes a system with equations,
> establishes the domain of each parameter via measurement or specification,
> and then runs those equations over those domains to produce results that
> can be repeated and objectively assessed by everyone, not just one person
> poking a scope probe around one instance of a circuit.
You can not model a HF PA without know what the components
behave like at radio frequencies. The only way to know that is to
measure the components. By the time you measure the
components, you might as well just have measured the
components as a group in the actual circuit.
If you measure the actual circuit, you can predict the chance of
any problem.
Modeling does not save time or give good answers in this
application because the model is generally too complex. All of the
modeling programs I've seen can't even handle an inductor properly,
let alone a vacuum tube.
> > My point is the model would take longer to construct than the
> > measurements would take, and almost certainly not be able to
> > include anywhere near everything.
>
> The measurement-and-argue approach to resolving the issues at hand has yet
> to succeed. Creating and validating a model is certainly more
> time-consuming than taking measurements. But after years of
> non-convergence, one should consider optimizing for results rather than
> time.
There is no measurement-and-argue approach, except for one
person who has little test equipment except for a grid dip oscillator.
Then when someone with test equipment makes a measurement,
he argues his GDO is better.
> > Please tell me the name of one that models a solenoid inductor
> > properly at radio frequencies. I really would like to purchase a copy.
>
> As previously stated, I am not an RF engineer. The last analog simulator I
> used was written in APL and ran on Multics, a predecessor of Unix. I am
> assuming that competent models exist for devices as physically
> straightforward as a solenoid inductor. While the answer to my question
> "Are you asserting that no modeling program properly models an inductor?"
> was not direct, the response implies "Yes", at least in the case of a
> solenoid inductor. That is surprising and, if true, dissapointing.
I can't say there aren't any modelling programs that will model a
solenoid inductor properly, all I can say is I haven't seen one. I've
tried a dozen programs, but I'm sure there are a dozen more.
If anyone else has seen a program that works, please let me know.
73, Tom W8JI
w8ji@contesting.com
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