What was it originally designed to do?

Well, this question is really sort of useless. Chances are the machine has been rendered obsolete by modern devices, decommisioned, so the original use has become a thing sentiment. A better question is what can this this do?

I have found that, for the most part, there are only a few root functions of old test equipment and the like. They are as follows:

Signal generators.
Supporting electronics. This is a vague term I admit, here we find things like amplifiers or filters.
Supporting passives. Attenuators, transformers, decade boxes, etc.
Measurement systems. Meters, charts, readouts.
Monitoring systems. Closely related to measurement, but including speakers, indicator lights etc.

Sound simple? Remember, there's still a more or less undefined aspect that will render a variable bandpass filter absolutely useless for any given audio project. Frequency.

Frequency range is the most important aspect to consider in an old signal generator. I highly advise anyone seriously considering putting some of these old beasts to work to have a firm understanding of frequency, and usable bandwidths. I'll just graze it here, then move on:

20hz (cps, cycles per second) - 20,000 (20khz) cps is the benchmark range of human hearing. Anything below this is LFO/CV territory anything above that can be considered as radio, and more or less useless for audio applications without some sort of modulation stage.

Something else I've noticed regarding pulse generators.. pulse width adjustable into hundreds of milliseconds is far more useful a source for audio than generators that can adjust into microseconds. Microsecond range is pretty much just ticks. It also merits mention that in the early days, it was a lot harder to get narrow microsecond pulses than larger millisecond ones, so sometimes huge, heavy and top of the line isn't the best option for audio.