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Tektronix Type D
Differential amplifier
D front view

Compatible with 500-series scopes

Produced from 1954 to 1969


Manuals – Specifications – Links – Pictures

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 Its final year in the catalog was 1968; it had been superseded by Type 1A7 and 1A6.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.


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.

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 = 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.


Some Parts Used in the D

Page Class Description Used in
12AU7 Vacuum Tube (Double Triode) twin medium-μ triode 122 181 502 502A 512 535 545 545A 545B 547 549 555 575 581 581A 585 585A C D E Q
5814 Vacuum Tube (Double Triode) twin medium-μ triode D
5879 Vacuum Tube (Pentode) sharp-cutoff pentode 112 512 D E