The Tektronix PG506 is a 1 MHz calibration generator plug-in for the TM500 system. It functionally replaces the 067-0502-01 in the "standard amplitude" mode, and the 106 in the "fast rise" and "high amplitude" modes.
There are (at least) two versions of the PG506. The older version has two relays that switch a low-pass (noise) filter into the 10 V and below ranges. The new version just has a capacitor across the output for these ranges.
Common failure modes: In case of low or no output on the 20 V and above ranges, check Q270, Q280 and Q290.