Jim, et al:

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.

John Andrews, W1TAG