The Tektronix Type R is a plug-in for 500-series scopes. It is designed to measure risetime of a NPN and PNP transistors, but it works well with FETs as well.
Type R can operate in grounded-emitter or grounded-base configurations. In the grounded-emitter configuration, it provides a variable collector voltage through a collector resistor which is used to sense the collector current. It provides a base bias voltage and a base pulse signal, fed to the base of the transistor through a resistor. The base pulse is generated by a mercury switch and its rise time is specified to be less than 5 nanoseconds. Base and collector bias conditions can be set independently.
The collector signal is AC-coupled to an amplifier whose output is fed to the oscilloscope. The Type R has its own on-board low-voltage, high-current regulated power supplies which feature germanium power transistors.