P
The Tektronix Type P plug-in is a step response calibrator introduced in 1959 for 500-series scopes. It applies a step signal to the vertical input (plug-in connector pins 1 and 3) of the scope. The step is generated by a mercury switch in the Type P and it has a 4 nanosecond risetime. The Type P is designed to simulate a Type K plug-in being driven by a Type 107 pulse generator. In this sense, it is designed to act as a standard, not as an ideal square pulse source. Why is this preferable to calibrating the mainframe using a square pulse? Would the high-frequency components of a square pulse cause problems?
The Type P was the only new plug-in for 1959, unless you count the upgrade from Type 53/54C to Type CA. It was dropped after 1963.
The Type P does not contain any tubes, transistors, or tunnel diodes. It does contain a selenium rectifier. The selenium rectifier in the Type P has four sections and full-wave rectifies the 6.3 VAC that is supplied by the scope mainframe on pins 13 and 14. The 120Hz (assuming 60Hz mains) component of the full-wave rectified waveform is applied to the coil of the mercury switch to drive the opening and closing of the contacts. An adjustable fraction of the DC component of the full-wave rectified waveform is applied to the coil of the mercury switch to create a constant component in the magnetic field to bias the switch contacts to the best operating point.
