W

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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

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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.

Operation

Type W has two signal inputs, "A" and "B", and a built in precision variable voltage supply, "V_C", 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−V_C, A−B, or V_C−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 V_C 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.

Pictures

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  Front view.

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  Top-left view.

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  Bottom view.

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  Block Diagram

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  Differential Comparator, initial version

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  Input Attenuators

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  Switching Diagram

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  A-phase (prototype) Type W

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  A-phase (prototype) Type W

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  A-phase (prototype) Type W

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  A-phase (prototype) Type W

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  A-phase (prototype) Type W