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The Tektronix Type 3B3 is sweep unit introduced in 1963, intended for use with the 561A. It works fine in other 560-series scopes. It provides a calibrated delay from 500 nsec to 10 seconds after the trigger event, before sweeping. Delayed sweep allows the operator to "zoom in" on regions of interest in a waveform. The 3B3 provides an intensified mode that indicates the selected region of interest in the delayed sweep by showing the entire waveform with the trace brighter in the selected region. Triggering is done using a 2mA germanium tunnel diode. The trigger source is buffered by a 7895 Nuvistor triode cathode-follower driving a differential amplifier formed by two 2N2207 germanium PNP transistors. The collector current switches the tunnel diode when a triggering event occurs.