|[AMRadio] AM Usage with Linear AMPS|
recycler at swbell.net
Tue Nov 23 00:33:43 EST 2004
The plate efficiency at full output under practical conditionsis
usually of the order of 50 to 65 per cent. With less than the
full output, the efficiency is proportional to the driving
voltage. When the signal to be amplified is a carrier wave
modulated 100 per cent, the carrier amplitude is half the peak
amplitude to be handled. The efficiency for the unmodulated wave
is then half the maximum efficiency, or 25 to abour 32 per cent
under ordinary conditions. The average efficiency of a linear
amplifier used with amplitude-modulated waves is hence relatively
low, because ordinarily the wave is fully modulated only a small
part of the time; even when fully modulated, it is at or near the
crest value for only a small fraction of the modulation cycle.
The peak output power that can be developed by a tube operating
as a linear amplifier is approximately the same as the power
developed by the same tube in Class-C amplifier operation, or it
may be slightly greater since the linear amplifier does not
operate at peak level continuously. Since the peak power of a
fully modulated wave is four times the carrier power, a tube used
as a linear amplifier is capable of developing something between
one-half and one-fourth as much carrier power as the output
attainable from the same tube operated as a Class-C amplifier.
A pair of 6146's operating at 600VDC put out 100 watts single
tone. This is the maximum that amplifier would make. The current
was about 260mA.
600VDC * 260mA = 156 watts input.
100 out, 56 dissipation.
600VDC * 135mA = 81 watts input.
25 out, 56 dissipation.
I realize this is pushing 6146's, better would have been 80 watts
PEP and 20W carrier.
The point is the efficiency as taken by meter readings. These
values can probably be validated on a host of existing 2x
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