large sonar amp transformers 4-400A size

[Opcom]

I found a bay of eight sonar amplifier channels, each one with a 4-400A socket and a large 5x5x4" transformer. The primary goes from the plate to B+ as usual in a single ended audio amp, and the secondary is tapped so the turns ratio is 12.5:1 or 17.5:1  (z=156:1 or 306:1).

Sangamo
TRANSF AF
822494
6036 (date?)

Primary DCR 3.5 Ohms, secondary DCR 0.02 Ohm

frequency response seems to be:
500Hz to 10KHz +/-0dB,
about 400Hz to 70KHz -3dB,
and 100Hz to 300KHz -6dB.

Primary inductance with secondary open is 100mH
Primary inductance with secondary shorted is 6.5mH
(I do not know exactly what this means)

When agitated slightly with a square wave, the ringing at the secondary to an open circuit is at 3.5MHz.

It's potted but the primary wire insulation and fittings look insulated for extreme voltages, at least 10KV.
I wonder if this would make a useful 100mH choke for high voltage use such as in a high-level low pass network etc.

The original intention of checking these was obviously to see if they would do audio.. not at frequencies I want to listen to. Anyone ever run into these kinds of things before?