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 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|
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.
Horizontal mode is set to alternating to show the pulse signal being triggered (A) and the delayed/magnified part (B).
Measuring rise time of a pulse. Delayed signal is scaled for 0-100% on graticule. Delay time is adjusted so the trace crosses the 10% level on the center line. Delta time is adjusted to so the delta-delayed trace crosses 90% on the same vertical line. Delta time readout indicates rise time directly.