The Tektronix Type W is a differential comparator plug-in amplifier for 500-series scopes. Its bandwidth varies from 23 MHz to 8 MHz depending on gain. Type W is faster 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. It was designed by John Horn.
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.
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.