The only indication of power is the “300 watts” label on the back.
I've wanted a silverface Twin or Pro Reverb since I was a teen.
The tube is fed a signal (from channel 2, or the “vibrato” channel, in the case of Fender reverb amps).
The tube’s output connects to a transformer, exactly as in a single-ended amp like a Champ.
But instead of being connected to a speaker, the output of the transformer in the reverb drive circuit is fed to a transducer in the reverb pan.
Turning up the channel volume allowed increased overdrive in the preamp section, with the overall volume of the amp controlled by the newly added master volume. But the engineers at Fender took it a step further, adding the ability to access more gain internally.
In 1968 Fender changed to the “silverface” control panel.