W

Manuals – Specifications – Links – Pictures

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 = 1	15 V
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.

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.

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

Pictures

• 

  Front view.

• 

  Top-left view.

• 

  Bottom view.

• 

  Block Diagram

• 

  Differential Comparator, initial version

• 

  Input Attenuators

• 

  Switching Diagram

• 

  A-phase (prototype) Type W

• 

  A-phase (prototype) Type W

• 

  A-phase (prototype) Type W

• 

  A-phase (prototype) Type W

• 

  A-phase (prototype) Type W