Vintage 1950's Ampex H-1390 (EV 623) Dynamic Microphone

This Ampex H-1390 dates from the 1950's. It was made for Ampex by Electro-Voice, and is identical to EV's model 623. Others have said that it's a high impedance, omnidirectional mic. What I've found is this - it's dual-impedance, depending on how it's hooked up. There's an Amphenol 4 pin jack on the mic assembly, and instructions for wiring are stamped on the side of the housing. Pin 1 is ground, pin 2 is high impedance, pin 3 is low impedance (150 ohm) return, and pin 4 is low impedance hot. I don't have the correct plug for the Amphenol jack, but I jury-rigged something to check the mic out. It works, though the sound seems a little thin to me. To my ear, the sound the high Z connection sounds a lot better than the low Z. That could just be my jack leg way of checking, though.
As far as the pickup pattern, it may be omnidirectional, but off-axis volume is a lot lower than on-axis. I couldn't find any "official" specs online, but it definitely doesn't sound like an omni mic to me. This mic is in GREAT shape, especially for being 60+ years old. There are a couple of dings and worn spots. It's lost a bit of its luster over the years, but still looks in amazing condition. All parts are original, including the stand. The switch works (down is on, up is off).
Truly a handsome mic to have, whether you want to record with it, or just show it off.
Just so's you know, I have another identical H-1390 that's in better shape as this one, for a little more $$. Works works the same.