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Author Topic: Power necessary to get disired power out of amp..  (Read 1637 times)
K2LGO
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Posts: 115




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« on: October 27, 2012, 05:01:53 PM »

If you are exciting your GG amp with 25 watts and you get the max amp output, what happens when you drive the same amp with 100watts Huh  Does the excess drive power appear in the amplifier output (and is actually not wasted) or will the power be dissipated in the amplifier tubes as heat Huh
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KH2G
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Posts: 252




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« Reply #1 on: October 27, 2012, 05:32:25 PM »

Excessive drive is self defeating on many fronts. You stand a good chance of burning something out and driving the Amp into non-linear operation most likely creating distortion. Never use more input power than required by the circuit design to get maximum efficiency,
Regards,
Dick KH2G
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K2LGO
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« Reply #2 on: October 27, 2012, 05:51:11 PM »

But that doesn't answer the question....
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W8JI
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« Reply #3 on: October 27, 2012, 05:57:16 PM »

If you are exciting your GG amp with 25 watts and you get the max amp output, what happens when you drive the same amp with 100watts Huh  Does the excess drive power appear in the amplifier output (and is actually not wasted) or will the power be dissipated in the amplifier tubes as heat Huh

If the amplifier is loaded to maximum output at 25 watts drive, and you increase drive more, much or most of the additional power is dissipated in the tube grids. What happens is:

1.) Grid current and grid dissipation goes through the roof

2.) Plate current increases a little bit

3.) Output power doesn't increase much

4.) Peak anode voltage goes way up, perhaps to destructive levels

You can see what happens here:

http://www.w8ji.com/demonstation.htm




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WB2WIK
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« Reply #4 on: October 27, 2012, 06:12:54 PM »

I'd want to know what the amplifier is.

If it can run max output with 25W drive, then of course anything beyond that just damages the amp and increases distortion; but what is the amp?
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K2LGO
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« Reply #5 on: October 27, 2012, 06:22:33 PM »

Thank you W8JI...that's the explanation I desired.....
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K0ZN
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Posts: 1543




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« Reply #6 on: October 27, 2012, 10:27:14 PM »

Read the part in W8JI's post again about grid dissipation "going through the roof".

A more basic translation:  In most cases, with severe over driving (you mentioned 100 W into an amp that only needs 25 W...i.e. 300% over drive), if you do it very long.....and "very long" in that case can be a few seconds with some tubes, you physically destroy the grid in the tube with consequences you probably can understand.
To wit:  grids (in most tubes used by hams) are relatively delicate fine wires and are easily damaged at truly abusive drive levels.

Moderate over driving causes your signal to splatter on adjacent frequencies, bother other hams and sound distorted. Translation:  you are demonstrating to other people listening that you don't understand how an amplifier works or how to properly tune it.

73,  K0ZN

« Last Edit: October 27, 2012, 10:33:00 PM by K0ZN » Logged
W9MMS
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Posts: 119




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« Reply #7 on: October 28, 2012, 09:27:02 AM »

Read the part in W8JI's post again about grid dissipation "going through the roof".

A more basic translation:  In most cases, with severe over driving (you mentioned 100 W into an amp that only needs 25 W...i.e. 300% over drive), if you do it very long.....and "very long" in that case can be a few seconds with some tubes, you physically destroy the grid in the tube with consequences you probably can understand.
To wit:  grids (in most tubes used by hams) are relatively delicate fine wires and are easily damaged at truly abusive drive levels.

Moderate over driving causes your signal to splatter on adjacent frequencies, bother other hams and sound distorted. Translation:  you are demonstrating to other people listening that you don't understand how an amplifier works or how to properly tune it.

73,  K0ZN


Read the path where he ask the Question.

>>> If you are exciting your GG amp with 25 watts and you get the max amp output, what happens when you drive the same amp with 100watts Huh <<<

In all fairness to Robert, he asked a very VALID question.
Nowhere in his post did he say that's what he is doing. He simply asked " What IF"
Isn't that how we learn? Isn't he demonstrating to us that he wants to learn?

I too learned something [ in DETAIL ] here today.

ROBERT, good question.

Tom, Thank you! For taking the time to explain in DETAIL the answer to Robert's question.

(((73))) Milverton
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