7A18

Manuals – Specifications – Links – Pictures

The Tektronix 7A18 is a general-purpose 75 MHz dual-trace vertical plug-in for 7000-series scopes. It was designed by Tom Rousseau. Model 7A18N is identical except it omits the readout circuits. The military designation is AM-6880/U.

The 7A18A is mostly identical to the 7A18 predecessor, but replaces the custom, low-inductance potentiometers for gain and variable gain setting with a FET attenuator and regular potentiometers.

The 7A18(A) uses a discrete front-end followed by M36 channel switch ICs for the vertical and trigger signals.

The 200 MHz 7A26 and 400 MHz 7A24 share the same front panel layout and operation.

Key Specifications

Input impedance	1 MΩ // 20 pF
Deflection	5 mV/div to 5 V/div in 1–2–5 sequence, ±2%
Bandwidth	0 – 75 MHz (DC), 10 Hz – 75 MHz (AC)
Noise	≤300 μV in 5 mV/Div
Offset range	(Option 06) ±200 Div equiv. from ±1 V in 5 mV/Div range up to ±200 V in 1 V/Div range (above that limited by maximum input voltage)
Features	Mode: CH1 only, CH2 only, Add CH1+CH2, Alternating, Chopped. CH2 can be inverted. Input sockets with contact ring for probe ×10 / identify information No bandwidth limiter switch
Weight	1.4 kg

Options

• Opt.1 – Deletes readout circuits (listed in 1971 catalog, later designated 7A18N/7A18AN)
• Opt.6 – This option replaces the IDENTIFY buttons with DC offset controls giving ±200 div offset range. It adds a fourth "DC offset" position to the input coupling switch. Opt.6 was first offered in the 1975 catalog.

Links

• See 7A12 for the history of the 7A18, 7A16A, 7A24, and 7A26.
• Tektronix 7A18 II Repair and Alignment (With a Deeper Look at the High Frequency Compensation) by Zenwizard Studios @ YouTube
• Tektronix 7A18 Repair and Function Generator Alignment by Zenwizard Studios @ YouTube

Documents referencing 7A18

Patents that may apply to 7A18

Patents that may apply to 7A18A

Prices

Year	Catalog price	In 2026 dollars
1971	$535	~$4,300
1976	$615	~$3,500
1980	$915	~$3,600
1984	$1,250	~$3,900
1990	$1,790	~$4,500

Pictures

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  7A18 Front

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  7A18 attenuator opened. One of the attenuation R/C modules has been unplugged to reveal the switch contacts.

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  7A18 attenuator, bottom (switch) side

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  A 7603 with two 7A18s

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  7A18 in 7613 mainframe

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  7A18 and 7A18N from service manual 070-1126-01

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  7A18N with "Identify" seen on an auction site - probably cobbled parts

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  7A18N Front

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  7A18N RHS switch cover removed

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  7A18N LHS switch cover removed

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  Broken bond between ganged gain pots

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  Broken bond between ganged gain pots zoomed

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  Intact epoxy between ganged gain pots

Development Prototypes

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  First prototype of 7A18

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  First prototype of 7A18

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  Second prototype of 7A18

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  Second prototype of 7A18

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  Third prototype of 7A18

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  Third prototype of 7A18

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  Third prototype of 7A18

7A18A

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  7A18A Front

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  7A18A left side. The step attenuators can be seen on the left, the amplifier board on the right.

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  7A18A right side. The circuit boards on top carry the readout circuitry.

Option 06

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  7A18A Opt.06 Front. AC/GND/DC switches have an extra rightmost "DC Offset" position enabling the offset controls.

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  7A18A Opt.06 left side (rear). Note the two blue 10T-potentiometers for offset voltage adjustment.

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  7A18A Opt.06 - offset controls take the place of the Identify buttons on the standard model.

Components

Some Parts Used in the 7A18

Some Parts Used in the 7A18A