Consider that for years, the typical rule for an amplifier "stage" was a power gain, or multiplication factor of between ten-to-one and fifteen-to-one, more or less.
A small box that boosts your radio from 20 Watt peaks to 200 Watt peaks, for example. Ten to one.
Rule of thumb for a 75-Watt peak-output-amplifier would be to drive an amplifier meant to deliver between 750 and 1200 Watts.
The power-gain factor tends to be higher for the AM carrier than it is for the modulation peaks. Causes them to over-exaggerate the carrier power, and under-deliver peak modulated power. It helps a lot to have a way to set the radio's carrier power lower than the normal barefoot level. This allows you to compensate for the amplifier's tendency to show too much carrier. Running the radio with full barefoot carrier level when driving amplifiers will reduce the audio level they hear at the other end, unless you can turn down the carrier to compensate. You may hear this particular audio issue described as a "tight" audio sound at the other end.
Not sure whether or not your amplifier should deliver 75 Watts peak power, or 75 Watts of average power. On AM, that's a big difference. Simply describing it as "75 Watts" does not narrow this down a lot.
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