181

The Tektronix Type 181 is a time mark generator introduced in 1955. There is a benchtop version, the 181, and a rackmount version, the RM181. MOD 110 substitutes a oven-stabilized 1MHZ crystal oscillator, the CO181, thereby achieving 2 parts per million frequency stability in a 24 hour period, the same stability as the 180A.

Internally, the 181 is similar to the 180. The oscillator drives a chain of synchronized monostable multivibrators. Each multivibrator is triggered by the output of the previous stage, and cannot be triggered again for the duration of its pulse width. In the 181, these pulse width ratio of one stage to the next is 1:10. The result is that when a stage triggers on a pulse at its input, it propagates that event to its output, but inhibits the next nine pulses. It does this by time, not by counting. After a stage returns to its resting state, it is triggerable again. So it triggers once every ten input pulses.

The 181 also provides a 10MHz output. This is generated a 10MHz resonator that is driven by an amplified and waveshaped copy of the 1MHz crystal oscillator output. Since it is a harmonic, the 10MHz output has same frequency percentage accuracy is the reference oscillator.

The power supply of the 181 produces +300V and -150V regulated voltages and +400V, -8V, and -25V unregulated. The voltage reference is a 5651 tube. The output tubes for both regulators are 12B4 and the feedback amplifier tubes are 6AU6. The 181 does not contain a fan or a thermal cutoff.

• Tektronix 181 Manual (PDF)

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  181

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  RM181

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  CO181 oven-stabilized oscillator

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  Block diagram

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  oscillator and multiplier

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  frequency dividers

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  switching detail

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  power supply