Genral Radio gear was very versatile. They made lots of equipment that could work together. and so make test and measurement configuration. I have for instance, all my bridges set near each other. This way they share things like oscillators and detectors. This amplifier was made in the same line of thoughts. It has no internal psu, I needs a powersupply that also is used for Unit oscillators.
This is a tube operated push pull amplifier. It does not have the usual output transformer that limmits the frequency response.