A gorgeous part in search of a project! There are about a dozen of these, new and in original boxes sitting around the shop. The FJ-125 weighs 10 kg and is just under 18 cm long. It has a single 34 volt secondary rated, interestingly, at 11 amps DC. Built-in to the case is a “swinging choke.” A swinging choke’s inductance varies in proportion to the current running through it. This allows improvements in power supply regulation. The choke is rated .050 henries @ 1 ampere/.01 henries @ 11 amperes. The case is hermetically sealed and has output terminals that pass through glass seals. There is also an electrostatic shield between the primary and secondary. I thought about designing a single-ended transistor amplifier around this transformer.