To: <amps@contesting.com>
> Date: Mon, 18 May 1998 16:26:12 -0500
> From: Jon Ogden <jono@webspun.com>
Hi Jim,
I said:
> >The tubes anode system, so far as that time-varying resistance, does
> >not come into play. We are only looking at a termination for that
> >system, so source impedance does not concern us greatly.
You replied:
> Source impedance does not concern us??? Tom, I think you need to go back
> and re-read your initial RF transmission line theory textbooks.
Hold on there Jon. There is enough of this personal attack BS on this
reflector. My general policy is when I see such insulting dribble, I
delete the post at that point. I'll continue this one time, because
you do have a technical point.
> source vs. load impedance doesn't concern us then why don't we just run
> PAs and transmitters into any SWR?
We present the correct impedance to the anode, and that impedance
matches the time-integrated impedance of the anode. The anode simply
gives the tank a "tug" at the correct time (the tube is a resistance
that varies with time).
Matching the tube's source impedance in an non-linear (through the
duration of a cycle, I don't mean non-linear so far as power drive
vs power output) less than 360 degree conduction angle system
requires the tank have a smoothing effect on that impedance, mush
like a mechanical pendulum.
Like the mechanical equivalent, you would have to match at the
harmonic frequency and at the particular time-averaged impedance that
provides maximum energy transfer at that frequency and power level.
The goal is NOT to transfer power (unless we are building a
frequency multiplier stage), but to de-Q the system or reduce gain.
You can get an excellent idea how well you have done at achieving
that goal by measuring what the anode "sees" when driving the
external system. You will have no idea at all what you are doing if
you stick a GDO downstream and look for dips.
It is an impedance problem, not a resonance problem.
> Although I must say that the explanation given by Ian White does make the
> most sense. By applying series to parallel conversions and doing good
> old fashioned network analysis, we can actually make a 100 Ohm resistor
> look like a couple of K-Ohms at a given frequency. So in a sense it does
> absorb the energy.
What "energy"? If the system is stable, there is no energy except
normal harmonic and IMD related products of non-linear
amplification of excitation.
prevent the amp from taking off.
> Now, I don't mean to start a war, but you and Rich Measures (AG6K) say
> about the same thing regarding the function of suppressors. So where is
> your beef with him? You can answer that one personally to me if you wish.
Do you really think all this personal insults belong in a
technical forum? I don't.
I've said all along the nichrome suppressor can do the same thing
as any other system, if you don't care about HF losses. Where
people are being misled is in the "my way or no way" view, and
especially by claims everyone else in the world, from Dick
Erhorn to Buzz Miklos is not only dishonest but technically
incompetent.
Bad theory and abused physics hurts our ability to understand
problems, and harmful suggestions hurt our wallets. Name calling,
slander, and personal insults do not belong in an educational
forum. That is my "beef".
For one example, a suggestion is often made and repeated by one
person that the grid of an 8877 will dissipate hundreds of watts,
and that people should simply "remove" grid protection circuits and
use a resistor to protect the grid. It's common knowledge that even
fuses are notoriously unreliable at protecting sensitive components,
and certainly we all know resistors used to serve the function of
fuses would be even worse.
73, Tom W8JI
w8ji.tom@MCIONE.com
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