7B85
The Tektronix 7B85 is a 400 MHz delaying timebase for 7000-series scopes. The trigger circuit is similar to that of the 7B80. The digital delay differentiates the 7B85 from the 7B80.
The 7B85 uses a 155-0185-00 digital voltmeter IC (U686). A ramp generator is started when the trigger signal arrives. The delayed sweep is started when a comparator detects that the ramp has reached a control voltage, set by the front panel knobs on the 7B85. The control voltage is proportional to the amount of delay. The digital voltmeter in the 7B85 digitizes the control voltage and displays it on the oscilloscope readout, thereby providing the operator with a precise readout of the delay. Another way of setting up a precisely delay timebase is to use a time mark generator such as the 180A, 181, 184, or 2901.
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