Carl,
>I dont follow your statement Peter or is it a language
>problem again? (;
> Tom repeatedly bashes the super cathode circuit and Bill
> Orr in particular.
I'm not bashing the Super Cathode circuit or Orr, just the
misapplication of what WAS a great circuit in one particular
application. I also don't like a bad idea being forced down
people's throats, such as repeated pressure to use a bad
system. This is actually exactly like the nichrome thing.
Something that can serve a purpose in a specific limited
case gets extended to another application or touted as a
general rule without any real care or thought to the
functioning in the other applications.
Let me make a specific example for both, which are the same
examples I have given dozens of times.
1.) If I wanted to use a device at or near the frequency
where it oscillated and had no practical means of correcting
the problem other than adding loss at the operating
frequency, I'd add loss or de-Q the device. Resistive
conductors of any type would work. This is why the old old
layouts with tubes that were unstable, having long thin
leads and tons of internal capacitance, sometimes used
nichrome or stainless. There just was no practical cheap way
to add losses close to the operating frequency. Some cavity
designs or modern designs where tubes are pushed up to the
operating limit add intentional losses in conductors to
stabilize the PA.
The only problem I have is when a solution good for one
application becomes a religion and all the science or
logical thought flies out the window.
2.) I've stated time and time again the Collins 30S1 was an
excellent application of negative feedback through a
partially floating control grid. It was an AB1 amp, so the
control grid resistance is very high. This makes a divider
work really well. It had a grounded screen, and so it had
excellent shielding from input (cathode) to output. It was
not dependent on the grounding of the control grid through a
very broadband very low impedance path to be stable. The
screen did all that.
The problem I have with the general application of that good
system to amps that have low or varying control grid
resistance and that depend on the control grid being
grounded for input to output shielding is lifting the grid
destabilizes the amplifier and often adds IMD through
uncontrolled feedback. It does everything you don't want to
do and it can be proven, both on paper and in a test.
There seems to be a tendency from outside the logical
technical community to think that if a certain behavior or
idea is disagreed with or wrong, it means EVERYTHING the
other person does is wrong. For example if a certain idea is
wrong about an antenna, some people think that means the
antenna will be a dummy load and no contacts will be
possible. Everyone, you and I included Carl, make mistakes.
It's if we learn from those mistakes and how we treat or
interact with others pointing them out or discussing ideas
that makes us good or bad.
Most people of reasonable intellect are mostly right. There
always have been a few widely published people who seem
bright but have many more mistakes than accurate
information. This is much more prevalent in amateur radio
because texts are not peer reviewed than in scientific
publications, since the peer review process sorts this out.
The ARRL Handbooks go through a lengthy peer review, and the
remaining nonsense is largely edited out after a few
printings. The RSGB Handbooks are the same. Unfortunately
the Radio Handbook never went through a process like that,
so a few really bad ideas stayed in it year after year. This
doesn't mean the author was a bad person, it doesn't mean
the book is useless, it just means it has some glaring bugs
that were never corrected.
The fastest way to learn is to talk to someone who disagrees
with you and listen to TECHNICAL points. The slowest way to
learn is to waste time insulting them, or waste time
misconstruing or distorting what they say.
> Yet you say it suggests excellent IMD re: Pappenfus.
Properly applied it does. Everyone agrees on that.
Improperly applied to any or every system in the world or
applied outside the boundaries of good engineering it is a
bad idea.
What is so difficult to understand about that?
By the way, the reason I can write a long post like this in
two minutes is I save my old hot topic posts and can cut and
paste. :-)
73 Tom
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