That little amp is made so you can set the variable in such a way that it will dead key about the same as your radio, then when you modulate they swing like crazy ( only on AM mode) up to the output of the 2290 transistor in them.
This is why they are called a modulator.
They really are only good for AM, they sound really crappy on SSB, and they look really good making the watt meter swing all over the place.
I know we played around with them for a while back when i first got started in radio.
Texas star says that 4 watts in will net 75 out.
They also say that 20 watts peak will give you 100 ( peak ) out, but if you run it that hard the first thing to burn up will be the variable resistor that controls the dead key.
I would not run more than a single final radio into one, and not let the radio swing more than around 10/12 watts into it with audio.....IMHO
73
Jeff