The 155-0064-00 is a custom IC hybrid developed by Tektronix in the early 1970's, primarily as a vertical output amplifier for oscilloscopes.
It is packaged in a 12-pin TO-8 stud mounted can. Maximum power dissipation is 4 watts. The rise time is specified as 470 ps (equiv. bandwidth 745 MHz).
According to Modification 050-1014-00, Vertical Output Microcircuit Replacement, the emitter resistors need to be selected according to a code printed on the device.