> >Now I didn't test every PA in the world, but the case where anode C is
> >more than distributed capacitance in the PA and the lead between the two
> >C's happens to form a step-up transformer doesn't occur in any PA I
> >have....even though Rich claims it can.
>
> That doesn't mean it can't happen - only that you haven't seen it.
To be more specific:
It means I have not seen it in PA's where Rich claims the
bandswitch is damaged by VHF oscillations.
> >Tell me the flaw in my measurement method, exciting the anode of
> >the tube at the anode with a high impedance bridging source and
> >measuring voltage along the tank system.
>
> Getting a sufficiently high impedance of R very high in series with
> absolutely j0.
The R only has to be a value somewhat higher than the dynamic
impedance of the anode in operating conditions, unless you buy
into the theory that power grid tubes with no plate current can
oscillate with considerable energy.
Ignoring the anode resistance can make all sorts of odd theories
work.
> >Remember we have to destroy the switch, which is further
> >downstream....
>
> Assume the stray capacity to ground from the switch end of the first
> section of the tank coil series resonated at the parasitic frequency with
> the first bit of tank coil?
Then the input impedance is reduced.
> I'm saying you cannot explicitly rule out the possibility of step up as
> far as the tank capacitor, or even to the switch. The probability of it
> happening is pretty mind boggling low as you need the resonances of
> several sets of components to all tie together. About the same as my wife
> winning the first prize in the lottery this weekend. But not impossible.
I can measure it. If you wife looks at the lottery payoff, and it is a
different number, the chances of her having won are what we can
consider zero.
> After all, even a stopped analogue clock is right twice a day!
'
Not one without any hands. When a person says something
happens in a specific device, and then measurements prove it
can't, it is time to re-think the speculated cause of the problem.
Now like you, I'm not saying an oscillation can't damage a PA. I'm
just saying the most likely scenario is an oscillation at or near a
frequency where the tank is resonant.
I'm sure Rich's suppressors would help PA's like Clipperton L's,
because they oscillate on or near ten and 15 meters. They aren't
the only way to fix the problem, but they de-Q the tank near ten
and 15 meters.
Conventional suppressors, while behaving the same or better at
VHF as nichrome varieties, don't de-Q the system at HF nearly as
much.
73, Tom W8JI
w8ji@contesting.com
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