CG5001
The Tektronix CG5001 is a programmable calibration generator plug-in for the TM500 system.
The 1983 Tektronix Catalog, on page 379, says:
The CG 5001 requires either a TM 5003 or TM 5006. The CG 551AP is a TM 500 version of the CG 5001 and requires a TM 506 Mod JB, TM 515 Mod UB, or RTM 506 Mod JB. The CG 5001 is not compatible with TM 500 power module mainframes.