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Tektronix 7B85
400 MHz Delaying Timebase
Tektronix 7B85 Delaying Timebase plug-in

Compatible with 7000-series scopes

Produced from 1976 to 1990

Manuals – Specifications – Links – Pictures

The Tektronix 7B85 is a 400 MHz delaying timebase for 7000-series scopes with digital delay and delta time read-out capability, typically used in the 7800 Series, e.g. 7844. It does not support X-Y mode.

The delay function differentiates the 7B85 from the otherwise similar 7B80. The 7B87 is also similar to the 7B85 but provides an acquisition clock for a digital storage mainframe instead of a delay.

The 7B85/7B80 combination was introduced in 1976 to replace the 200 MHz 7B71/7B70 that had no digital delay read-out. For the 7104 1 GHz-class scopes, the 7B15/7B10 provide the functionality of 7B85/7B80.


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
  • Digital read-out of delay and delta times
  • Variable Trigger Holdoff
  • Peak-to-peak Auto Triggering


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.

The 7B85 uses the +50 V supply provided by the mainframe.





These are examples of measurements with a 7B85 in the Horizontal A and a 7B80 in the Horizontal B compartment (of a 7904).

Horizontal mode is set to alternating to show the pulse signal being triggered (A) and the delayed/magnified part (B).