7A13

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Tektronix 7A13
100 MHz Differential Comparator
7A13 front panel (older version with mechanical voltage display)

Compatible with 7000-series scopes

Produced from 1969 to 1992

Manuals
Manuals – Specifications – Links – Pictures

The Tektronix 7A13 is a "differential comparator" vertical plug-in for 7000-series scopes, i.e. a fast differential amplifier with adjustable DC offset. It is one of the first 7000 series plugins. It was designed by Bill DeVey and released along with the first 7000-series scopes in 1969/1970, and was made until the 7000 series was retired in 1992.

The 7A13 was known internally as the XA3 until just before release when the final nomenclature was determined.

Operation

Older versions display the comparison (offset) voltage through a mechanical dial. Newer versions (from 1976 on) display the comparison voltage on an LED panel meter. In addition, this voltage is brought out through a front panel connector so it can be measured externally.

In differential mode, a ±10 V common mode signal can be present at the inputs without attenuation. Either input can be switched to the comparison voltage, which is settable to four digits by a 10-step switch and a 10-turn potentiometer. In this comparator mode, the offset range is effectively 10,000 divisions.

On the 1 mV/Div to 50 mV/Div ranges, the gate resistors can be disabled by an internal switch, raising DC input impedance to "approximately infinite" (as indicated by a front panel lamp).

Key Specifications

Bandwidth 100 MHz (in 7700 or faster mainframes)
Risetime 3.5 ns
Deflection 1 mV/Div – 5 V/Div (1–2–5 sequence)
Common-mode range at least ±10 V from 1 mV/Div to 5 mV/Div, ±100 V from 10 mV/Div to 50 mV/Div, ±500 V from 100 mV/Div to 5 V/Div
Overdrive recovery to within 2 mV in 1µs (at 1 mV/Div)
CMRR ≥10,000:1 for 10 Vp-p or less, 100 kHz to 1 MHz, decreasing to 500:1 at 10 MHz with 1 Vp-p, 200:1 at 20 MHz with 1 Vp-p
Input impedance 1 MΩ // 20 pF
Comparison voltage −10 V to +10 V
Vc reading accuracy

Mechanical version: 0.1% of reading + 5 mV
DVM version: 0.1% of reading + 3 mV

Warmup time 5 minutes for short-term measurements, 1 hour for best stability

Links

Documents Referencing 7A13

Document Class Title Authors Year Links
Tekscope 1969 V1 N5 Oct 1969.pdf Article Introducing the New Generation 1969
Tekscope 1969 V1 N6 Dec 1969.pdf Article A New Logic for Oscilloscope Displays 1969
Tekscope 1970 V2 N5 Oct 1970.pdf Article Amplitude Measurement to Better Than 1% 1970
Tekscope 1972 V4 N5 Sep 1972.pdf Article A Practical Approach to Differential Amplifiers and Measurements Fred Beckett 1972
Tekscope 1972 V4 N6 Nov 1972.pdf Article Differential Amplifiers and Measurements, Part 2 Fred Beckett 1972
7000 series brochure March 1973.pdf Brochure 7000 series brochure, March 1973 1973

Patents that may apply to 7A13

Page Title Inventors Filing date Grant date Links
Patent US 3584174A Push-button switch apparatus having cam actuated switch contacts and selective illumination means Tony Sprando Peter S Winkelmann 1969-06-09 1971-06-08

Power Consumption

The power consumption of a 7A13 was measured to be:

  • +50 V: 75 mA
  • −50 V: 66 mA
  • +15 V: 238 mA
  • −15 V: 204 mA
  • +5 V (logic): 279 mA
  • +5 V (lights): 228 mA

Internals

In the older version, the comparison voltage is generated from a precision zener supplied from either positive or negative 50 V rail, followed by a 10-step switched divider made of 0.1% resistors to select the first digit. For the lower three digits, a ten-turn potentiometer with a mechanical digital readout is used. The V/Div switch changes the decimal point on the readout, which is implemented through small light bulbs above the dial with plastic light guides to make the decimal point appear between the digits. In contrast to the back-lit switches, the decimal point lamps are supplied from logic +5 V so they also work in mainframes without switch light supplies, e.g. the 76x3s.

In the newer version, the zener-derived reference voltage is always positive. A 10-turn pot for coarse selection combines with a single-turn pot for fine control. The resultant voltage is displayed on a 4-digit simplified DVM built around a Fairchild 3814 4½ digit DVM controller. (S/N B250000+ switched to a Siliconix LD122/LD121A chipset.) For negative values of VC, an opamp polarity inverter circuit is switched in.

The 7A13 uses the ±50 V supplies provided by the mainframe.

Repair issues

The 7A13 uses twelve miniature relays similar to those used in the 7A11. These are very rare. The 7A11 repair report at amplifier.cd describes a possible replacement with a modern component. See also the IK1ZYW link below.

Early 7A13 plug-ins were made with a mechanical counter for reading out the comparison voltage. The plastic gears in this counter don't age well. The plug-in can still be used when the counter fails, by using an external voltmeter to monitor the comparison voltage, Vc.

Later 7A13 plug-ins use an LED readout instead of the mechanical counter. The LED readout is much less problematic.

Links

Pictures

Older version (1970-1975, mechanical meter)

Newer version (1976-1992, LED meter)

Components

Some Parts Used in the 7A13

Part Part Number(s) Class Description Used in
148-0034-00 148-0034-00 Discrete component miniature DPDT relay 5A48 7A11 7A13 7A14 7B70 7B71 7503 7904 7904A
148-0035-00 148-0035-00 Discrete component miniature SPDT relay 7A13 7A14 7B70 7B71
148-0050-00 148-0050-00 Discrete component miniature SPDT relay 7A13
148-0054-00 148-0054-00 Discrete component miniature SPDT+SPST relay 7A13
148-0055-00 148-0055-00 Discrete component miniature SPDT+SPST relay 7A13
Fairchild 3814 156-0306-00 Monolithic integrated circuit 4½ digit dual-slope DVM controller 7A13 7L13 7L18 DM501
Siliconix LD121A 156-1305-00 Monolithic integrated circuit 4½ digit integrating ADC (digital section) 7A13 DM501A
Siliconix LD122 156-2205-00 Monolithic integrated circuit 4½ digit integrating ADC (analog section) 7A13