7B85

The Tektronix 7B85 is a 400 MHz delaying timebase for 7000-series scopes, typically the 7800 Series, e.g. 7844. The trigger circuit is similar to that of the 7B80. The digital delay differentiates the 7B85 from the 7B80. The 7B87 is similar to the 7B85 but provides an acquisition clock for a digital storage mainframe instead of a delay.

Key Specifications

Sweep	5 s/Div to 10 ns/Div in 1-2-5 sequence, ×10 magnifier down to 1 ns/Div, variable to ×2.5
Triggering	to 400 MHz
Features	Variable Trigger Holdoff Peak-to-peak Auto Triggering

Internals

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 delayed timebase is to use a 7D11 digital delay module, or even a time mark generator such as the 180A, 181, 184, or 2901.

Pictures

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  Left rear

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  Left front

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  Right front

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  Right rear