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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.

From Tekscope Vol.8 No.1, 1976:

Les Larson developed the trigger circuitry and served as Project Manager for the 7B80 and 7B85. The sweeps were designed by Bruce Hofer and the DVM and related logic by Paul Farley. Much credit is due Art Metz for his work on the trigger input 1C which includes the peak-to-peak automatic trigger circuitry. Gene Andrews, Program Manager, provided overall direction for the project.

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
  • 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.

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



Year 1977 1980 1984 1987 1990
Catalog price $895 $1,200 $1,700 $1,940 $2,400
In 2021 Dollars $4,100 $4,000 $4,500 $4,700 $5,100




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).

Custom ICs used in the 7B85

Page Model Part nos Description Designers Used in
155-0049-00 M079G 155-0049-00 155-0049-01 155-0049-02 sweep control with lockout Bill DeVey 335 464 465 466 475 475A 475M 485 5B31 5B40 5B52 5B42 5B44 7B53A 7B80 7B85 7B87 7B92A 7B90P 7B10 7B15 SC502 7B42N AN/USM-281C 067-0657-00
155-0090-00 M059 155-0090-00 155-0090-01 155-0090-02 four-decade counter Mike Metcalf 7D01 7D12 7D15 7B85 7J20
155-0109-00 M120B 155-0109-00 155-0109-01 trigger Gary Vance 5B25N 5B31 5B40 5B42 5B44 5S14N 7B50A 7B53A 7B80 7B85 7B87 7B81P 7B90P 7S14 7612D SC502 SC503 SC504
155-0126-00 M121 155-0126-00 trigger source selector and P-P auto amplifier Art Metz 7B50A 7B80 7B85 7B87 7B81P 7B90P
155-0171-00 M150A 155-0171-00 4-decade counter, latch and D/A converter Mike Metcalf 7B85 7D01 7D12 7D15 7J20
155-0185-00 M187 155-0185-00 4-digit digital voltmeter Don Larson 7B15 7B85 7B87