H. Adam Stevens wrote:
I have a class A audio amp (BAT VK500) and it definitely gets cooler when
The Carmina Burana gets louder.

Take a lesson from the power companies. They run coolest when their
output impedances are the lowest. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Until one breaker goes and the rest of the grid can't handle the load.
;^)))))))))
73,
H.
"W5DXP" wrote in message
...
H. Adam Stevens wrote:
I have a class A audio amp (BAT VK500) and it definitely gets cooler
when
The Carmina Burana gets louder.

Take a lesson from the power companies. They run coolest when their
output impedances are the lowest. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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(Richard Harrison) wrote:
Floyd Davidson wrote:
"Unless of course that shuts down ,or even destroys the source devices
in the process (adjustable load gets hottest for least power to the
source as proposed by H. Adam Stevens)."

If you are going to quote me, the least you could do is quote
what *I* said, without editing it to suit your needs.

Regardless, whatever it is that the rest of this nonsense is
supposed to mean, it certainly doesn't relate to what I posted.

H.`s variable load can determine a match because maximum power transfers
if the load impedance is the conjugate of the source. But, least power
input may not coincide with maximum power output. Low internal source
impedance as compared with the load impedance usually is more efficient,
but not necessarily so. With impedance produced by switched-off time as
in the Class C amplifier, impedance is not only a function of internal
loss.

A Class A amplifier has constant power input so that the more power
delivered to a load, the less power is dissipated in the amplifier.

Simple determination of source impedance is to divide the open-circuit
voltage by the short-circuit current out of the device. That requires a
source impedance that is the same at matched loading as with a shorted
load. As Floyd notes, the extremes, open and shorts, can shut-down or
destroy from too much voltage or current.

Near the region of a conjugate match, less severe voltage and current
are likely. Maximum power transfer to the load occurs at the conjugate
match point. Heat rise would be the likely cause of damage to a
transmitter at maximum output. Power output measurements can be made
quickly to limit transmitter and load temperature rise in and around the
load impedance which gives maximum power output. A versatile load can be
used to determine the conjugate match and thus the source impedance.

The transmitter may not be designed to deliver maximum power output even
momentarily and may have built-in protection to prevent it.

Feedback may not increase maximum power output without regard to
distortion. In an audio amplifier, the output impedance may be made to
look like a short to the speaker and thereby put the brakes on its
movement as it tends to ring on after excitation. The same feedback
lowers distortion at a given power level, or said another way increases
power output for a given level of distortion, but maximum power output
without regard to distortion is unaffected by the feedback. R-F
amplifier negative feedback likewise has no effect on the all-out
maximum power.

Best regards, Richard Harrison, KB5WZI


--
Floyd L. Davidson http://web.newsguy.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

Floyd Davidson wrote:
"Unless of course that shuts down, or even destroys the source device in
the process."

Floyd was commenting on H. Adam Stevens` suggestion of how to measure
source impedance.

I appended the gist of H.`s comment in parentheses to define "that" in
Floyd`s statement.

I am sorry I misplaced the quotation marks which should have been placed
as they are above. I don`t disagree with either Floyd or H.

Best regards, Richard Harrison, KB5WZI

Richard,

If you do indeed need help, it's far more help than I can give you.
My posting was not in jest, nor was it to poke fun at you or your
postings. I was dead serious about it.

Cheers,
Tom

Richard Clark wrote in message . ..
On 17 Aug 2003 21:12:52 -0700, (Tom Bruhns) wrote:
Richard, I'm seriously worried about you. Was that posting, and many
of the others I've seen from you recently, a plea for help? I'm sure
we can come up with appropriate help lines for you to call, if only
you will tell us what's at the root of your problem.

Regards,
Tom

Hi Tom,

You only need drive down the road some 25 minutes if you are serious.
Less time than that spent in all these postings that have you worried.
I've driven to Mukilteo 5 days a week for several years and its not
all that far and almost a straight shot especially with you on the
speedway.

When can I expect you? ;-)

73's
Richard Clark, KB7QHC

H. Adam Stevens wrote:

"W5DXP" wrote in message
Take a lesson from the power companies. They run coolest when their
output impedances are the lowest. :-)

Until one breaker goes and the rest of the grid can't handle the load.
;^))))))))) 73, H.

Incidentally, the argument that Thomas Edison used to prove that
power distribution systems would never be AC is that they would
burn themselves up trying to provide maximum power transfer. He
never conceived that they would be more interested in efficiency
than maximum power transfer. :-) So why can't we have a 95%
efficient RF power amplifier?
--
73, Cecil http://www.qsl.net/w5dxp



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On 18 Aug 2003 09:37:59 -0700, (Tom Bruhns) wrote:

Richard,

If you do indeed need help, it's far more help than I can give you.
My posting was not in jest, nor was it to poke fun at you or your
postings. I was dead serious about it.

Cheers,
Tom


Hi Tom,

Yes, I have noticed the 30 cent jump in the cost of gas. ;-)

How about lunch at Lake Stevens then? I drove that for a couple of
years too, back when your outfit was called HP. I worked in Larry
Whatley and Nick Pendergas's group during the Marysville to L.S. move
(to set a time frame). 1,000,000 lines of Pascal FFT code in that
project. It was fun and I still have a lot of drawings of waveforms
generated.

For those who are interested in the nuances of FFT's (and why their
own implementation transforms lack resolution or dynamic range); my
tenure provided me with a wealth of insight that is commonly
unimplemented in current discussions here and generally in trade
publications.

73's
Richard Clark, KB7QHC

Roy Lewallen wrote:

H. Adam Stevens wrote:
If the source is matched to the line, is the reflected wave dissipated as
heat in the source?

Nope. I've shown this definitively a number of times on this newsgroup.

Yep, by assuming something that is true only by definition. :-)
If the source is hidden in a black box and includes a circulator
with load, the reflected wave *IS* dissipated as heat in the
source. For some phases of reflected energy, the dissipation does
increase. You say it is because of the mismatch but the mismatch
is because of the reflected waves. So which came first, the mismatch
or the reflected waves? I suggest that the mismatch will not happen
until the reflected waves arrive. Try it with a one second long
transmission line.
--
73, Cecil http://www.qsl.net/w5dxp



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Aren't the switching amps used in AM broadcast highly efficient?
Do folks still use class C amps in FM service?
(It's been decades)
H.
NQ5H

"W5DXP" wrote in message
...
H. Adam Stevens wrote:

"W5DXP" wrote in message
Take a lesson from the power companies. They run coolest when their
output impedances are the lowest. :-)

Until one breaker goes and the rest of the grid can't handle the load.
;^))))))))) 73, H.

Incidentally, the argument that Thomas Edison used to prove that
power distribution systems would never be AC is that they would
burn themselves up trying to provide maximum power transfer. He
never conceived that they would be more interested in efficiency
than maximum power transfer. :-) So why can't we have a 95%
efficient RF power amplifier?
--
73, Cecil http://www.qsl.net/w5dxp



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I've made homebrew transmitters with efficiencies exceeding 85%. See for
example Fig. 2.97 on p. 2.36 of the new _Experimental Methods in RF
Design_. Sokal and Sokal got better than 90% as I recall with their
Class E designs.

Roy Lewallen, W7EL