X381

The X381 is an experimental 560-series timebase plug-in. It appears to have used a 3B1 plug-in as a starting point.

Front Panel

The front panel has a Nixie display which is driven by a Fairchild 9960 decoder/driver IC.

The front panel hss a two-position slide switch with positions marked "SEC" and "Hz".

Optical Disk

Within the X381, there is an octagonal aluminum enclosure containing a backlit disk of film that is rotated by a front panel knob. The disk functions similarly to a quadrature optical encoder, but instead of generating just two signals, it generates several signals. There are pairs of human-readable numbers on the disk at each rotational position. These numbers are visible outside of the enclosure. Each pair of numbers, when multiplied, gives a product very close to 10,000. Since the two numbers have a reciprocal relationship, one number probably represents the sweep speed in time per division while the other number represents the sweep speed in frequency, e.g., of a waveform that repeats in one horizontal division.

Motorized TIME/DIV

The TIME/DIV control is two concentric knobs.

Outer Knob

The outer knob is the coarse TIME/DIV control, and goes in 1-2-5 steps from 2 sec/div to 1 μs/div. The front panel knob rotates this rotary switch. However, the switch can also be controlled by a motor in the plug-in. When the coarse TIME/DIV control is rotated using the front panel knob, the motor's gear is mechanically disengaged from the rotary switch shaft.

The rotary coarse TIME/DIV switch controls the rightmost nixie tube, which shows the TIME/DIV units.

Inner Knob

The inner knob is probably a vernier TIME/DIV control. The inner knob rotates the optical disk and a precision rotary potentiometer, Tektronix part number 311-0537-01. Each radial position of the disk produces a pattern of light/dark in the light pipes coming out of the disk. The patterns encode vernier TIME/DIV values. Each light pipe goes to a photosensor, which controls the left three decimal nixie tube. The inner knob, like the outer knob, can be rotated by turning the front-panel knob, but is also motor-controlled, presumably to enable automated measurement.

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  backlit with flashlight for photo

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  backlit with flashlight for photo

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Photos of Optical Disk

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