The Tektronix TU-3 is a calibration fixture plug-in for 580-series scopes that was replaced by the Type 84 which additionally contains a pulser to adjust vertical step response.

calibration fixture
Tek TU-3

Compatible with 580-series scopes

Produced from (?) to (?)

(All manuals in PDF format unless noted otherwise)

The TU-3 consists of dummy loading resistors, two cathode followers, and a bistable multivibrator.

The dummy loading resistors are connected to each regulated supply of the oscilloscope when the LOAD switch is set to HIGH, to test for the maximum power supply loading condition.

The cathode followers decouple the input signal from the oscilloscope vertical amplifier and elevate the vertical amplifier input to the required voltage (about +50 volts).