John A,
With the proposed 100 watt transmitter output limit here in the U.S., we
can
be a little more conservative with audio amplifiers used as transmitter
PA's. I have been playing with a nominal "8 ohm" amplifier (actually two "4
ohm" amps in bridging configuration), and using a 1:2 transformer that
presents 12.5 ohms to the PA when terminated in 50 ohms. As noted in the LF
Handbook, the output impedance of these amps can rise with frequency, and
there is plenty of power available with the 100 watt restriction.
I tend to be in agreement with Mr. Mal on this subject. (Mark this date)
Most amplifiers designed for audio use are slew rate limited when it comes
to a full bore 137K sine wave because of the output devices. These amps
usually check out OK on the bench with dummy loads but under 'real life'
conditions there's little margin for transients - where the transient power
(current times voltage) seen by the output devices can unknowingly be many
times the maximum ratings.
Bill A
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