Anybody ever heard of these? They came out of some Ampex tube duplicating chain electronics, I think. They're 600:600 ohm +10dB max. Model number is: TFIR-X10AJ and the Ampex part number is 27045.01A. They're a little larger (1 9/16" x 1 9/16" x 2") than UTC a-20s but otherwise are similar looking. Made by Malmac Mfg. Co. Has anyone come across these before?