The Tektronix 546 is is a 50 MHz scope that takes letter-series and 1-series plug-ins like a 547, but without synchronized alternating timebases.
Functionally, it is like a 545B, but with tunnel diode triggering and 50 MHz vertical bandwidth.
There is also a rackmount version, the RM546.
The 546 is less common than the 545 or 547.
The project lead for the development of the Tektronix 544, 546, and 547 was Bob Rullman.
Specifications please add