The Tektronix CFG253 is a stand-alone 3 MHz function generator.

Tektronix CFG253
Function generator
Tektronix CFG253

Produced from 1991 to (?)

Manuals
(All manuals in PDF format unless noted otherwise)

It appears to be Tek-rebranded OEM unit, similar to a Kenwood FG-272.

Key Specifications

Frequency 0.3 Hz to 3 MHz in 7 ranges
Amplitude 0 to 2 Vp-p or 0 to 20 Vp-p into high impedance (0-1/0-10 V into 50 Ω), ±10 (5) V offset
Signal types Sine, Square, or Sawtooth, additional TTL output
Sine distortion <1% from 10 Hz to 100 kHz
Sweep 1:1 to 100:1, 0.5 Hz to 50 Hz
Symmetry control 5:1 change

Pictures