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The Tektronix Type W is a differential comparator plug-in amplifier for 500-series scopes, designed by John Horn.

Key Specifications

Deflection 1 mV/Div to 50 V/Div, 1–2–5 (6-position) and 4-position decade attenuator
Input impedance 1 MΩ // 20 pF (either input)
Bandwidth 26 MHz (23 MHz below S/N 7000) @ 50 mV/cm; 8 MHz @ 1 mV/cm
Common Mode Range ±15 V after INPUT ATTEN
CMRR DC Coupled: 20000:1 DC to 20 kHz, 500:1 at 500 kHz; AC Coupled: 1000:1 at 60 Hz
Signal ranges
Maximum Input Voltage (S/N 7000-up)
DC Coupled 350 V
AC Coupled 500 V
Maximum Input Voltage (S/N 101-6999)
INPUT ATTEN = 10 150 V
INPUT ATTEN = 100 ±350 V (DC Coupled); 500 V (AC Coupled)
INPUT ATTEN = 1000 ±350 V (DC Coupled); 500 V (AC Coupled)

Type W is faster (bandwidth 23 MHz to 8 MHz depending on gain) than its Type Z predecessor, and it extends performance in terms of sensitivity, reaching 1 mV/div. It achieves 20,000 to 1 common-mode rejection at DC and low frequencies.


Type W has two signal inputs, "A" and "B", and a built in precision variable voltage supply, "VC", which is controlled by a ten-turn pot and can vary from either −1.1 V to +1.1 V or −11 V to +11 V. A mode switch selects between displaying A−VC, A−B, or VC−B. The "A−B" mode is particularly useful for displaying the current in a sense resistor, while the other modes provide "slideback" measurements of small variations superimposed on a large constant. An output of VC is provided on the front panel for precision measurements.

Unlike the Type Z, Type W has two gain axes: a decade attenuator and a 1−2−5−10−20−50 selector, reminiscent of Type D from ten years before.

Type W is the only letter-series plug-in with an "infinite resistance" input mode selectable at the front panel. (Types 1A5 and 1A7 have an internal jumper that can be cut.)

Early production Type W in a 556 mainframe won't meet spec for overdrive recovery time, because an overdriven W passes enough common-mode to the mainframe vertical amp to saturate it. At S/N 3270, this was fixed, by adding another stage to attenuate CM. The new "output amp" circuit board clips onto the rear bulkhead; significant hand mods are required on the chassis. This was also offered as Modification kit 040-0447-00 to retrofit existing instruments.

Type W was created with a pair of type 8056 Nuvistors in the front end. In 1971 (S/N 7000), following the lead of Type 1A7, the Nuvistors were replaced by JFETs to reduce drift. Mod kit 040-0590-00 was offered for existing instruments.

In the letter-series timeline of differential comparators, Type W, introduced in 1965, follows Type Z and precedes Type 1A5.

Type W uses three type 8416 tubes, the 12V version of the 6DJ8.


Some Parts Used in the W

Page Class Description Used in
6DJ8 Vacuum Tube (Double Triode) dual triode 132 502 502A 503 504 515 516 519 529 RM529 533 535 543 544 545 545A 545B 546 547 549 555 556 565 581 581A 585 585A 661 2A60 2A63 3A8 1121 1A4 67 81 82 86 3B1 3B4 1S1 B O W Z Telequipment S32A Telequipment D52 Telequipment S52 Telequipment S51 Telequipment Type A
8056 Vacuum Tube (Triode) low-voltage Nuvistor triode 422 502 W 1S1 3A7 3S3 3T4 5T3 10A1