D

The Tektronix Type D is a differential amplifier plug-in for 500-series scopes.

Type D was the most sensitive plug-in of the original four. The bandwidth depends on the gain, ranging from 2 MHz at 50 mV/div to 300 kHz at 1 mV/div. There are two axes of sensitivity setting: a decade attenuator in front of a gain switch. This scheme would be reprised in Type W.

It displays the difference between two input signals, with a common-mode rejection ratio of 10,000. It has six tubes, on a shock-mounted subchassis to avoid microphonics.

Along with Types A, B, and C, Type D was introduced with the 531 and 535 in 1954.

At the time it was called Type 53D. It was briefly renamed 53D/54D in 1955 with the introduction of the 541 and 545. This quickly changed to 53/54D, and finally shortened to just "D" in 1959 with the introduction of the 5xxA scopes. Its final year in the catalog was 1968; it had been superseded by Type 1A7 and 1A6.

K, L, and T are tied for longest production life, at 16 years. B, D, and G are next at 15 years.

Lavoie Laboratories produced an unauthorized clone, the Lavoie LA-265-D.

Internals

Instruments below serial number 3462 used a pair of 5814 tubes at the input; later production used 12AU7's. These two tube types have different heater currents, and because the heaters are series-wired, you cannot switch from one type to the other without circuit modification.

At least some instruments after S/N 3462 (using 12AU7) were built with old stock of chassis marked "5814" and "53D/54D".

Key Specifications

Deflection	1 mV/Div to 50 V/Div in 1–2–5-10-20-50 sequence and 1-10-100-1000 sequence
Input impedance	1 MΩ // 47 pF (either input)
Bandwidth	2 MHz with MV/CM MULTIPLIER set to 50; 300kHz with MV/CM MULTIPLIER set to 1
CMRR	10000:1 with MILLIVOLTS/CM set to 1, 1000:1 otherwise
Signal ranges

Range	Common mode dynamic range*
MILLIVOLTS/CM = 1	±2.5 V
MILLIVOLTS/CM = 10	±25 V
MILLIVOLTS/CM = 100	±250 V
MILLIVOLTS/CM = 1000	±500 V

• In practice, Type D behaves well up to about +/-15V if the CM signal is either a brief excursion or a constant. If the CM varies slowly, DC shift in the input tubes will degrade CMRR.

Pictures

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  Front

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  Chassis

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  Rubber support for elimination of microphonics

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  Chassis bottom

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  Early Schematic

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  Late Schematic

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  Late Attenuators

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  Front View (vertical position knob not original)