Ian said:
"The grid in a "grounded grid" amplifier is a case in point. It is
behaving as an inductive length of wire, terminated inside the tube by
some distributed capacitance to the anode and the cathode... which in
turn are connected somehow back to ground. Certainly you have a circuit
there, with inductance and capacitance in the loop, so it will have a
resonance; and if you can couple a GDO into it, you'll see a dip.
But that resonance belongs to the whole circuit, involving the anode and
cathode and all their associated components. There are too many unknowns
in that loop to understand what the frequency of the observed dip might
be telling us about reverse feed-through from the anode back to the
cathode.
>I must admit that I've never had a lot of use for GDO
Me neither, because it's so difficult to understand what a dip actually
means, except in the very simplest cases.
The GDO is deceptively simple instrument. The trick is to tell when it
stops being simple, and starts being deceptive."
In the past few days, at one extreme, a number of learned gentlemen have
suggested that they neither use nor understand the dip meter, and that the
use by others is easily understood. They suggest complex, expensive
instruments to evaluate circuits.
At the other extreme, it is suggested that the dip meter is used as a basis
that tubes, as wired in normal amplifiers, have internal circuits that
resonate at 80-120 MHz, and that this is the root of the unwanted parasitic
oscillation. This conclusion has been reached through the use of a dip
meter measuring the grid, as connected, of Power Amplifier tubes. As I
recall the sequence of revelations, the first article on the parasitic
solutions appeared in Ham Radio. However, later articles by the same author
admitted that the cure did not work, but came up with a real cure - all
based upon the results of the dip oscillator.
With the publication of the later articles on parasitic solutions, through
the use of magic wire, life became simplified for the average ham. All one
needed to do was incorporate the magic wire into an amplifier, plus a few
other magic items, and the grids will be tamed - as proved with a dip meter,
and all generally would be well.
I looked up the word religion in Wikipedia and found the following. Note,
because religion encompasses a lot of things, I have removed some words that
were clearly not applicable. However, the definition has no added words:
"Religion is a human phenomenon that defies easy definition. It is commonly
understood as a group of beliefs or attitudes concerning an object (real or
imagined) or system of thought considered to be highest truth, and the
practices associated with such system of thought."
It occurred to me that the adoption of the use of the dip meter and magic
wire to solve the mysterious parasitic phenomena is a religion and it
simplifies life a great deal. It means that the only piece of test
equipment you need is a dip meter (preferably a Kenwood dip meter). It also
eliminates any testing at all in the amplifier, and reduces design to a
minimum, simply by the use the magic wire.
Now, a number of learned men are challenging this simple basis of life,
taking the position that we should abandon our dip meters and suggest that
we buy vector network analyzers, spectrum analyzers with sweep generators or
perhaps only a simple network analyzer - suggesting that life is much more
complex than another leader has promoted. One has even taken a position
that parasitic suppressors are not even required, while at the same time
actually building and selling an amplifier without one. Heresy, I say.
Centuries earlier, life was simple, when all of the planets and suns were
found to revolve around earth. Then, some heretic with fancy equipment
claimed that the simpler system was flawed. He developed a much more
complex system, which soon brought others over to his side.
I have seen lately that in a number of fields certain people have proclaimed
themselves to be ethicists - who are able to judge others, and their
actions. Seems like a noble field, and some even get paid for such a title.
It seems like a good field because it allows you to judge others, using
whatever you feel like using as a basis.
What I am proposing is that I become a parasitic ethicist. The only problem
is that I am not sure what I should be studying or what I should adopt as a
standard. And, although I have no clue what I am doing, I can still see a
benefit having an ethicist on the panel, to make ethical and moral decisions
on such a lofty subject as parasitics. I can also see the need for an
ethicist on the use of a dip meter, but I, as yet, have no clue on how I
would rule on that one.
I am also still trying to understand why Ian and Peter sometimes stay up
into the middle of the night to participate. It seems that they are trying
to stay one step ahead of the others, doing their thinking and writing while
we are sleeping away.
73, Colin K7FM
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