The Tektronix Type T is a timebase plug-in primarily intended for use in the 536 X-Y scope. It contains trigger and sweep circuitry. The typical use of a Type T plug-in is as the X-axis plug-in in a 536, to make the 536 behave like a normal oscilloscope instead of an X-Y scope. However, there is no capability for internal triggering – a jumper must be connected from the Vertical Signal Out on the 536 to the External Trig on the T.
Plugging a Type T in a vertical slot of a normal 500-series scope produces a raster, and using the scope's Z-axis input this allows a crude video display.
The banana jack on the back of the plugin is to provide retrace blanking when used in the horizontal slot of a 536
The Type T was introduced in 1957 and dropped after 1972, the same as its primary host, the 536. (Types K, L, and T are tied for longest production life, at 16 years, B, D, and G are next at 15 years.)