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Tektronix 3B1
10 MHz time base
Tektronix 3B1 front

Compatible with 560-series scopes

Produced from 1962 to (?)

Manuals – Specifications – Links – Pictures

The Tektronix 3B1 is a time-base plug-in introduced in 1962 for 560-series scopes. 10 MHz is is the maximum trigger frequency. The calibrated sweep rates go from 1 s/Div to 500 ns/Div.

There is a switch that enables 5 × horizontal magnification, which makes the fastest sweep 100 ns/Div. The 3B1 has a delayed sweep and a regular sweep.


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The 3B1 uses vacuum tubes, bipolar junction transistors, and tunnel diodes.

The trigger input goes through the int/ext switch and then the ac/dc coupling switch, and then a 7895 cathode follower. The output of the cathode follower drives one base of a 2N2207 PNP differential amplifier which has a tunnel diode in the collector load. The tunnel diode generates pulses when it switches back and forth between its two stable voltages, which are capacitively coupled to a 2N2501 NPN common emitter amplifier.

The delay pickoff circuit is a 6DJ8 differential amplifier that compares the sweep ramp voltage with a knob-controlled DC voltage which determines the point where the delayed trigger starts. The DC voltage is made by a ZZ1000 80 V reference passed through a potentiometer-variable voltage divider.

When the sweep ramp exceeds the control voltage, a 2.2 mA tunnel diode in the plate load of the differential amplifier switches state.