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Tektronix 7A42
350 MHz four-channel logic triggered amplifier
7A42 front view

Compatible with 7000-series scopes

Produced from 1984 to 1990


ROM images

(All manuals in PDF format unless noted otherwise)
Manuals – Specifications – Links – Pictures

The Tektronix 7A42 is a four-channel 350 MHz plug-in for 7000-series scopes. It is a double-wide plug-in, with signal outputs and mainframe readout only using the left slot.

It was specifically designed for logic signals (TTL, ECL, CMOS) and supports triggering based on Boolean conditions of the four inputs. A fifth trace, "Trigger View", displays the trigger function output or external clock input.

There are two sets of conditions, A and B, that can be individually selected or paired in an "A then B" mode called nested triggering, where the occurrence of condition A arms the trigger and condition B causes the trigger to be generated. The trigger can be qualified by an external clock. A trigger filter control, variable from 0-300 ns, allows events shorter than the selected length to be suppressed. A TTL-level "reset" input will inhibit the trigger if active.

Selected by an internal jumper, either the trigger signal, or the "A then B" interval, is available on a front-panel trigger output. This can e.g. be routed to a counter for time measurement or event counting.

The input V/Div setting can only be seen in the mainframe's readout. There is a jumper to allow the readout to work in a 7854 mainframe. The trigger level is set digitally and shown on a 7-segment display.

Tektronix recommended the P6131, 300 MHz, 10 MΩ ×10 probe, and the P6230, 1.5 GHz, 450/50 Ω ×10, variable-offset probe for ECL circuits.

The 067-1155-99 calibration fixture is specific to the 7A42.

Key Specifications

Bandwidth 350 MHz
  • 0.1 / 0.2 / 0.5 V/Div (TTL mode)
  • 20 / 50 / 100 mV/Div (ECL mode)
  • each direct or through 10:1 probe
  • always DC coupled
Input impedance 1 MΩ // 15 pF or 50 Ω
Max. input voltage
  • at 1 MΩ: 25 V (DC+peak AC) below 36 MHz, down to 3 VAC at 300 MHz
  • at 50 Ω: 5 VRMS during any 1 ms interval
Trigger level
  • −1.27 to +1.28 V (TTL mode) in 10 mV steps
  • −254 mV to +256 mV (ECL mode) in 2 mV steps (or ×10)
Hysteresis 40 mV (TTL), 8 mV (ECL) (or ×10)
  • NiCd battery to preserve front-panel control status
Weight 2.8 kg / 6.2 lb


Documents Referencing 7A42

Document Class Title Authors Year Links
42W-5588.pdf Application Note Advanced Triggering Techniques Roger Ensrud 1984

See also


The 7A42's functions are controlled by an Intel 8085A microprocessor, with code in three 2764 EPROMs (a fourth ROM socket is unused). The front-panel pushbuttons are handled by an Intel 8279 keyboard controller.

Each of the four 119-1517-00 input attenuator modules contains five 148-0145-00 miniature bi-stable relay actuators. These have four long pins plugging in to the base board, driving two solenoids that move aa yoke which is held in the last active position by a permanent magnet. The yoke moves a pair of contact springs that directly short corresponding pads on the thick-film ceramic substrate. The relay coils are wired in a 4×5 matrix.

The 7A42 contains its own switch mode PSU, based on an SG3524 controller, that generates +5 V, −2 V and −5 V from the mainframe's ±50 V rails.

There is a NiCd backup battery that allows the unit to retain its last configuration.

A 555 timer implements a 15 ms "real-time clock" and watchdog reset, another drives a beeper.

An internal jumper enables partial compatibility with a 7854 mainframe in storage mode (displaying any single channel, 1+2 in ALT, or 3+4 in ALT only). There are no restrictions with the 7854 in analog mode.




Some Parts Used in the 7A42

Part Part Number(s) Class Description Used in
148-0145-00 148-0145-00 Discrete component miniature bi-stable relay actuator 7A42 119-1517-00
155-0038-01 155-0038-00 155-0038-01 Monolithic integrated circuit 5-bit current source D/A converter 7A42 7D13 7D14 7M13 T4005
155-0078-00 155-0078-xx 155-0273-00 155-0274-00 Monolithic integrated circuit broadband amplifier 464 465 466 468 475 475A 475M 485 7834 7844 7854 7904 R7903 R7912 7912AD 7912HB 7104 7A16A 7A16P 7A24 7A26 7A42 067-0587-01 067-0680-00 AM503 PG502 PG508 DC510 DC5010 FG5010
155-0236-00 155-0236-00 Hybrid integrated circuit channel switch 2445 2465 7A42
ICM7218 156-1621-00 156-1622-00 Monolithic integrated circuit 8-digit, 7-segment LED driver 7A42
Intel 8085 156-1088-00 Monolithic integrated circuit 8-bit microprocessor 308 468 4025 7A42 7D02 AFG5101 AFG5102