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Old February 26th 05, 05:21 AM
Tom Ring
 
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Reg Edwards wrote:

If a conjugate match matters two hoots, or is involved in the slightest way
with the design of power amplifiers or any other sort of amplifier, why
don't tube manufacturers state the internal resistance or impedance in tube
date sheets?



So I guess you just connect your tubes or transistor finals directly to
the coax?

I mean, since it doesn't matter...

Tom
K0TAR
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Old February 26th 05, 05:23 AM
Ken Smith
 
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In article ,
Tam/WB2TT wrote:
[...]
When device people talk about "matching", they mean matching the load to
what the transistor wants to see, which is not the conjugate of the output
impedance.


Actually, in this case, I was speaking of matching the transmitter's
output to the load. The transmitter already contains gawd knows what L
and C components etc. The OP has a completed transmitter and a hunk of
wire. If he matches the wire to what the transmitter wants to see, the
transmitter will be happy. If he causes a reactive current to flow that
the designer did not design for he will cause added heating in the output
device. If the designer did a good job, the transmitter will protect its
output devices and thus end up producing less power.

Also if he makes the real component of the impedance vary from what the
designer intended, the output power will decrease. Which direction gets
limited by the Vcc and which by the protection circuit depends on the
collection of Ls and Cs inside the transmitter.




--
--
forging knowledge

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Old February 26th 05, 05:26 AM
Cecil Moore
 
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Ken Smith wrote:
Now lets assume that you slightly decrease the resistance. Since we are
assuming that this is a well designed case, we can assume that the
designer took steps to ensure that the output devices would be protected
from excess currents.


Let's assume the designer is an amateur who didn't provide
any protection for his tube's output. The lower the resistive
load, the more current the output device draws until it fails.
What is the output impedance of the device?
--
73, Cecil http://www.qsl.net/w5dxp


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Old February 26th 05, 05:35 AM
Cecil Moore
 
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Rich Grise wrote:
Evidently, the guy's never tuned up a 40 meter pi-net output transmitter. ;-)

If that's not impedance matching, I don't know what it is! (Oh, "Load line"
matching? What are the two parameters of the load line? Voltage and Current,
right? What's the slope of the load line? Impedance!)


And there's the catch. If the load line is the source
impedance, the load (not the designer) effects the source
impedance.
--
73, Cecil http://www.qsl.net/w5dxp


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Old February 26th 05, 05:52 AM
Cecil Moore
 
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Reg Edwards wrote:
If a conjugate match matters two hoots, or is involved in the slightest way
with the design of power amplifiers or any other sort of amplifier, why
don't tube manufacturers state the internal resistance or impedance in tube
date sheets?


When I first became a ham, transmitters didn't have
any protection at all. They would keep putting out
more and more power until the final or power supply
got too hot.

My 6L6 went out during a contest in the 50's. All I
had to replace it with was a metal 6V6. What's the
source impedance of a 6V6 plugged into a 6L6 socket?
--
73, Cecil http://www.qsl.net/w5dxp


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Old February 26th 05, 05:53 AM
Reg Edwards
 
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The phrase "output impedance" in connection with amplifiers is ambiguous and
likely to result in arguments.

The correct description is "internal impedance" or "internal resistance" and
should always be used.
----
Reg.


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Old February 26th 05, 05:56 AM
Cecil Moore
 
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Ken Smith wrote:
If you then
put in the output device protection they didn't include, you end up with
the matching as I explained elsewhere.


SWR foldback is part of impedance matching?
--
73, Cecil http://www.qsl.net/w5dxp


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Old February 26th 05, 06:42 AM
Larry Brasfield
 
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"Reg Edwards" wrote in
message ...
The phrase "output impedance" in connection with amplifiers is ambiguous and
likely to result in arguments.


I suppose the same could be said of any block that is
susceptible to having some feedback put around it.
Therefore the term "output impedance" should never
be used at all. And of course, any term that could, or
has ever been known to lead to an argument, with any
uninformed person that might come along, should be
eliminated from our vocabulary.

Uuugh. Mmmmph. Me drag woman to cave by hair.

The correct description is "internal impedance" or "internal resistance" and
should always be used.


Nonsense.

If I wanted to speak of an impedance inside of some
circuit, I might loosely speak of it as "internal", but in
any useful discussion, it would be spoken of as either
an output impedance or an input impedance, and, with
most people I have such discussions with, there would
be no need to add that some unknown additional feed-
back not part of the present discussion could alter the
observable impedance.

I hope your post was a troll.

--
--Larry Brasfield
email:
Above views may belong only to me.


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Old February 26th 05, 08:27 AM
John Woodgate
 
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I read in sci.electronics.design that gwhite wrote
(in ) about '1/4 vs 1/2 wavelength
antenna', on Fri, 25 Feb 2005:

I'm sorry, but they are not. Nor are any power amps that I know of.
Efficiency (and thus necessarily output swing) is what matters for power
amps. To maximize swing requires load line matching, not impedance
matching.


What is a 'load line'? A straight line on an I/V graph? What does the
gradient of that line represent?
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
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