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

It has high gain, and the bandwidth depends on the gain, ranging from 2 MHz at 50 mV/div and up, to 300 kHz at 1 mV/div.

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.

Type D was introduced with the 531 and 535 in 1954 as Type 53D. It was briefly renamed Type 53D/54D in 1955 with the introduction of the 541 and 545, and then quickly renamed Type 53/54D. Its name was then shortened to Type D in 1959 with the introduction of the 5xxA scopes. Its last year was 1968, having been superseded by the constant-bandwidth model 1A6.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.


Some production runs used a pair of 5814 tubes at the input while others 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.


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