11B1
The Tektronix 11B1 is a single time-base plug-in for the 647 and 647A, specified to trigger at frequencies up to 50 MHz.
It was introduced in 1964.
The 11B1 uses a 7586 triode to buffer the vertical signal at the input, and then a differential pair of NPN transistors that form a clipping amplifier.
The trigger detection is done by a Tek part number 152-125 tunnel diode, which is a selected TD3A.
