Chassis removed from very early Oahu amp brought in for repair.  (I reckon it's pre-WWII as it belonged to an old fiddler's father.) Blowing fuses on arrival- usual suspects proved to be the problem.  Shorted power supply cap was the culprit. Complete cap job and it sounded great!  Behind the non-original door is the field coil speaker.

Front of Oahu amp seen above. Very rough but a great sound.  Certainly one of the earliest amps I've worked.