The Tektronix Type B is a plug-in for 500-series scopes.
It is identical to Type A, with the addition of a ×10-gain AC amplifier which can be switched in to extend the vertical sensitivity from 50 mV/div to 5 mV/div.
Like Type A, Type B has its roots in the 1954 introduction of the 531 and 535, as the five-tube Type 53B, with 1x bandwidth of DC to 10MHz (limited by the mainframe) and 10x-AC bandwidth of 2 Hz to 9 MHz.
In 1959, Type 53/54B was renamed Type B, and it remained available through 1970.
The military version is known as the AM-1841/USM, which is the same as a 53/54B MOD601.