Dear Dick, LF Group,

I want to run something with an fixed voltage between 50 to 100 Volt,
depending on what transformer configuration I'm using.

One of the nice features of class D or other switching-mode amplifiers
is that they work much the same when the supply voltage is reduced,
except that the output power is also reduced. This means you can test
your PA (or tune up the antenna)with a 12V or less current-limited
supply and a few watts output, when there is very little chance of
damaging components. Then when you are happy all is working OK, connect
a higher supply voltage for QRO operation (however, the driver should
always be run from its normal supply voltage to ensure proper switching
operation of the output devices). It is quite possible to make voltage-
and current regulated supplies for QRO transmitters, but they are
usually more complicated and expensive than the TX they are supplying
power to.

Cheers, Jim Moritz
73 de M0BMU