The Tektronix PG506 is a 1 MHz calibration generator plug-in for the TM500 system.
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.