A couple of comments not covered by others.... *****

"Mont" wrote in message
. net...
Following is a note I received from a friend who earnestly believes that a
Class C plate modulated final requires approximately 200% (rather than
50%)
of the final power input to achieve 100% modulation. ... Thanks, Mont -
K0YCN
-------------------------------------------
Mont,
....
My goal is to be capable of 130% positive peak modulation with 375 watts
of
carrier output.

****** WHY?. What could be the possible benefit (thinking on terms of dB)?
This is what, 2 dB more power in the sidebands...? This is 69% more power
in the sidebands and 2dB is 56% more...


The Eimac 4-400...3000 volts...630 watts high level plate modulated
carrier output. So, 630 watts X 4 = 2520 watts pep capability.

***** PEP is a red herring here. I could be wrong because of the contorted
reasoning, but I believe he is confusing Peak power and PEP, but I can't be
sure 'cuz I don't completely understand what he is trying to reason out.
Peak Power is Vpk x Ipk
PEP is V(rms at the peak) x I(rms at the peak)


...375 watts X 4 X 1.30 = 1950 watts pos. peak.
Dividing that by 2 = 975 watts of peak audio output required...

**** This appears to be a location for a logic fault.


The 4-125 typical operation indicates 330 watts of AB1 is available....
*** Noted for later.


The negative vs. positive peaks will be controlled by a broadcast quality
Innovonics AM asymmetrical compressor limiter which I am currently using
in
the shack.

*** This may be a separate issue, but doesn't this suggest that the
modulator AND transformer must have the capability of handling the distorted
waveform from this "asymmetrical compressor " such that the low frequency
response extends low enough to get this extra plate voltage turing the
positive peaks?



... a 375 watt transmitter requires 187.5 watts of audio for
100% modulation. So, a 4-125, with 330 watts of capability, should be
more
than what is needed.

*** No argument here...

In practical terms this is very misleading.
*** paraphrased = " _I_ can't get _my_ circuit to work."


That is
why I been beating a dead horse for three years while two broadcast
engineers could not explain why I could barely attain near 100 modulation.
Little did I know that I was driving the pants of the poor 4-125's while
trying!

*** Are the RF amp and modulator operating properly in the first place?
*** Does he have the proper modulation transformer?
*** Is he even using a modulation transformer?
*** Is he confused between Peak power and PEP?

73, Steve, K9DCI

Hence, I ordered a custom built filament xfmr that will power two 4-400
modulators. Hope to have all that working in about two weeks.

73,