SMTD998
The SMTD998 (P/N 152-0177-02) is a 10 mA, 2 pF tunnel diode in a DO-17 "top hat" package.
It is used in the 067-0681-01, in the 7B92/7B92A and the 485.
The 152-0177-02 is very similar to the 152-0177-01, but has a tighter tolerance on Ip (±0.5 mA vs. ±1 mA for the -01).
(Is the 152-0177-02 simply a selected 152-0177-01? The 152-0177-02 is listed in the 067-0681-01 as being manufactured by Tektronix. Was it fabricated by Tektronix or just binned and/or selected by Tektronix?)