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7A18 - TekWiki

️Mon Oct 07 1968

The Tektronix 7A18 is a general-purpose 75 MHz dual-trace vertical plug-in for 7000-series scopes. Model 7A18N is identical except it omits the readout circuits.

Option 06 (first offered in 1975 catalog) adds offset voltage controls giving ±200 Div offset range. This option replaces the IDENTIFY buttons with DC offset controls, and adds a fourth "DC offset" position to the input coupling switch.

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
Option 06 offset range	±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

Links

Tektronix 7A18 II Repair and Alignment (With a Deeper Look at the High Frequency Compensation) @ Zenwizard Studios YouTube
Tektronix 7A18 Repair and Function Generator Alignment @ Zenwizard Studios YouTube

Documents Referencing 7A18

Document	Class	Title	Year	Links
7000 series brochure March 1973.pdf	Brochure	7000 series brochure, March 1973		1973	7A11 • 7A12 • 7A13 • 7A14 • 7A15A • 7A16A • 7A17 • 7A18 • 7A19 • 7A21N • 7A22 • 7B50 • 7B53A • 7B70 • 7B71 • 7B92 • 7CT1N • 7D11 • 7D13 • 7D14 • 7D15 • 7M11 • 7L12 • 7S11 • 7S12 • 7T11 • 7704A • R7704 • 7904 • R7903 • 7603 • R7603 • 7403N • R7403N • 7313 • R7313 • 7613 • R7613 • 7623 • R7623 • P7001
Tekscope 1977 V9 N1.pdf	Article	Counter and Oscilloscope Combination Makes Difficult Measurements	Emory Harry	1977	DC505A • 7B53A • 7A18 • 7603

Patents that may apply to 7A18

Page	Title	Inventors	Filing date	Grant date	Links
Patent US 3562464A	Cam actuated switch having movable and fixed contacts on circuit board	Howard Vollum • Willem H Verhoef • Tony Sprando	1968-10-07	1971-02-09	Cam switches • 2101 • 2701 • 2703 • 432 • 434 • 465 • 475 • 5A15N • 5A18N • 5A20N • 5A21N • 5A38 • 5A45 • 5B10N • 5B12N • 7A15 • 7A16A • 7A18 • 7A19 • 7A24 • 7A26 • 7B10 • 7B15 • 7B50 • 7B51 • 7B52 • 7B53A • 7B50A • 7B70 • 7B71 • 7B80 • 7B85 • 7B87 • 7B92 • 7B92A • 7D01 • 7D12 • 7D15 • 7J20 • 7S12 • 7T11 • 7T11A • AF501 • AM502 • AM503 • DC502 • DC503 • DC504 • DC505 • DM501 • DM502 • FG501 • FG501A • FG502 • FG503 • FG504 • FG507 • PG501 • PG502 • PG505 • PG506 • PG506A • PG508 • TG501 • SC502 • SC503 • SC504
Patent US 3719788A	Switch having ganged contacts mounted on opposite sides of circuit board	Ken Holland • Tony Sprando	1971-02-04	1973-03-06	465 • 475 • 5A38 • 5A45 • 7A15 • 7A16A • 7A18 • 7A19 • 7A24 • 7A26 • 7D15 • PG506
Patent US 3753170A	Step attenuator apparatus having attenuator stages selectively connected in cascade by cam actuated switches	Ken Holland	1971-02-10	1973-08-14	465 • 475 • 5A38 • 5A45 • 7A15 • 7A16A • 7A18 • 7A19 • 7A24 • 7A26
Patent US 3900711A	Electrical contactor assembly for high frequency applications	Ken Holland	1974-02-04	1975-08-19	465 • 475 • 5A38 • 5A45 • 7A15 • 7A16A • 7A18 • 7A19 • 7A24 • 7A26 • 7D15 • AM503

Prices

Year	1971	1976	1980	1984	1990
Catalog Price	$535	$615	$915	$1,250	$1,790
In 2023 Dollars	$4,100	$3,300	$3,400	$3,700	$4,200

Pictures

7A18 Front
7A18 attenuator opened. One of the attenuation R/C modules has been unplugged to reveal the switch contacts.
7A18 attenuator, bottom (switch) side
A 7603 with two 7A18s
7A18 in 7613 mainframe
7A18 and 7A18N from service manual 070-1126-01
7A18N with "Identify" seen on an auction site - probably cobbled parts
7A18N Front
7A18N RHS switch cover removed
7A18N LHS switch cover removed
Broken bond between ganged gain pots
Broken bond between ganged gain pots zoomed
Intact epoxy between ganged gain pots

Development Prototypes

First prototype of 7A18
First prototype of 7A18
Second prototype of 7A18
Second prototype of 7A18
Third prototype of 7A18
Third prototype of 7A18
Third prototype of 7A18

7A18A

7A18A Front
7A18A left side. The step attenuators can be seen on the left, the amplifier board on the right.
7A18A right side. The circuit boards on top carry the readout circuitry.

Option 06

7A18A Opt.06 Front. AC/GND/DC switches have an extra rightmost "DC Offset" position enabling the offset controls.
7A18A Opt.06 left side (rear). Note the two blue 10T-potentiometers for offset voltage adjustment.
7A18A Opt.06 - offset controls take the place of the Identify buttons on the standard model.

Components

Some Parts Used in the 7A18

Part	Part Number(s)	Class	Description	Used in
155-0022-00	155-0022-00 • 155-0022-01	Monolithic integrated circuit	analog multiplexer	147 • 148 • 149 • 335 • 468 • 1430 • 1441 • 1461 • 1900 • 1910 • 2220 • 2221 • 2230 • 5223 • 5403 • 5440 • 5441 • 5443 • 5444 • 5A38 • 7313 • 7403N • 7503 • 7504 • 7514 • 7603 • AN/USM-281C • 7613 • 7623 • 7623A • 7633 • 7704 • R7704 • 7704A • 7834 • 7844 • 7854 • R7912 • 7912AD • 7912HB • 7904 • R7903 • 7904A • 7934 • 7A12 • 7A18 • 7A18A • 7A18N • 7B52 • 7B53N • 7D10 • 7D11 • 7D12 • NT-7000 • P7001

Some Parts Used in the 7A18A

Part	Part Number(s)	Class	Description	Used in
155-0022-00	155-0022-00 • 155-0022-01	Monolithic integrated circuit	analog multiplexer	147 • 148 • 149 • 335 • 468 • 1430 • 1441 • 1461 • 1900 • 1910 • 2220 • 2221 • 2230 • 5223 • 5403 • 5440 • 5441 • 5443 • 5444 • 5A38 • 7313 • 7403N • 7503 • 7504 • 7514 • 7603 • AN/USM-281C • 7613 • 7623 • 7623A • 7633 • 7704 • R7704 • 7704A • 7834 • 7844 • 7854 • R7912 • 7912AD • 7912HB • 7904 • R7903 • 7904A • 7934 • 7A12 • 7A18 • 7A18A • 7A18N • 7B52 • 7B53N • 7D10 • 7D11 • 7D12 • NT-7000 • P7001