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The Tektronix 7A18 is a 75 MHz dual-trace vertical plug-in for 7000-series
{{Plugin Sidebar |
scopes.  The input impedance is 1 megohm in parallel with 20 pF. 
manufacturer=Tektronix | type=7A18|
Deflection factors go from 5 mV/div to 5 V/div.
summary=75 MHz dual channel amplifier|
image=Tek-7a18a-front.jpg |
caption=7A18 front view|
introduced=1971 |
discontinued=1992 |
series=7000-series scopes|
designers=Tom Rousseau|
manuals=
* [[Media:070-1126-01.pdf|Tektronix 7A18+7A18N Instruction Manual]] (OCR)
* [[Media:070-4329-00.pdf|Tektronix 7A18A Instruction Manual]] (OCR)
<small>
'''Alternates'''
* [http://bama.edebris.com/download/tek/7a18/Tektronix_7A18_Service_June1974.pdf Tektronix 7A18 Manual] @ BAMA
* [http://bama.edebris.com/download/tek/7a18a/tek-7a18a.pdf Tektronix 7A18A Manual] @ BAMA
</small>
}}
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 [[7000 series readout system|readout circuits]].


* [http://bama.edebris.com/download/tek/7a18/Tektronix_7A18_Service_June1974.pdf Tektronix 7A18 Manual (PDF)]
Option 06 (first offered in 1975 catalog) adds offset voltage controls giving ±200 Div offset range. 
* [http://bama.edebris.com/download/tek/7a18a/tek-7a18a.pdf Tektronix 7A18A Manual (PDF)]
This option replaces the IDENTIFY buttons with DC offset controls, and adds a fourth "DC offset" position to the input coupling switch.
* [http://w140.com/smb/7a18_7a18n_sm.pdf Tektronix 7A18 and 7A18N Manual (OCR, PDF)]
 
* [http://w140.com/smb/7a18a_sm.pdf Tektronix 7A18A Manual (OCR, PDF)]
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 [[M036|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.
 
{{BeginSpecs}}
{{Spec | Input impedance | 1 MΩ  // 20 pF }}
{{Spec | Deflection | 5 mV/div to 5 V/div in 1–2–5 sequence, 2% }}
{{Spec | Bandwidth | 0 – 75 MHz (DC),  10 Hz – 75 MHz (AC) }}
{{Spec | Noise | < 300 μV in 5 mV/Div }}
{{Spec | 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) }}
{{Spec | Features |
* Mode: CH1 only, CH2 only, Add CH1+CH2, Alternating, Chopped.  CH2 can be inverted.
* Input sockets with contact ring for probe &times;10 / identify information
* No bandwidth limiter switch
}}
{{Spec | Weight | 1.4 kg }}
{{EndSpecs}}
 
==Links==
* [https://www.youtube.com/watch?v=JZ76egcWH_4 Tektronix 7A18 II Repair and Alignment (With a Deeper Look at the High Frequency Compensation)] @ Zenwizard Studios YouTube
* [https://youtu.be/Cz9kxXKlWUw Tektronix 7A18 Repair and Function Generator Alignment] @ Zenwizard Studios YouTube
{{Documents|Link=7A18}}
 
==Prices==
{| class="wikitable"
|-
! Year
! 1971
! 1976
! 1980
! 1984
! 1990
|-
! Catalog Price
|align=right|  $535
|align=right|  $615
|align=right|  $915
|align=right| $1,250
|align=right| $1,790
|-
! In 2023 Dollars
|align=right| $4,100
|align=right| $3,300
|align=right| $3,400
|align=right| $3,700
|align=right| $4,200
|-
|}
 
==Repair issues==
===Attenuator solder joints===
The pins of the attenuator modules are connected to conductive traces on the ceramic substrate inside by low-temperature soldering, which can go bad.
Re-seating the module can temporarily restore the internal contact but will usually not fix the problem permanently.
Repair is possible by opening the click-locked lid and carefully resoldering.
 
===Variable gain pots===
These pots (R237A,B and R437A,B 315-0241-00) are bonded together - that bond can break which stops the gain push from working. Looking at a few 7A18s, I see that the design was changed at least once.
 
==Pictures==
<gallery>
Tek_7a18.jpg                                        | 7A18 Front
7a18-attenuator.jpg                                | 7A18 attenuator opened.  One of the attenuation R/C modules has been unplugged to reveal the switch contacts.
Tek 7A18 attenuator bottom.jpg                      | 7A18 attenuator, bottom (switch) side
Tek-7603-front.jpg                                  | A [[7603]] with two 7A18s
Tek 7a17 7a18 7b50a model3 cart.jpg                | 7A18 in [[7613]] mainframe
7A18 and 7A18N from 070-1126-01.png                | 7A18 and 7A18N from service manual 070-1126-01
Tek 7a18n.jpeg                                      | 7A18N with "Identify" seen on an auction site - probably cobbled parts
7A18N front.jpg                                    | 7A18N Front
7A18N RHS.jpg                                      | 7A18N RHS switch cover removed
7A18N LHS.jpg                                      | 7A18N LHS switch cover removed
7A18 R237A and B broken bond.jpg                    | Broken bond between ganged gain pots
7A18N split ganged gain epoxy bond split zoom.png  | Broken bond between ganged gain pots zoomed
7A18 intact epoxy bond between ganged gain pots.jpg | Intact epoxy between ganged gain pots
</gallery>
===Development Prototypes===
<gallery>
Tek 7a18 first prototype 1.jpg  | First prototype of 7A18
Tek 7a18 first prototype 2.jpg  | First prototype of 7A18
Tek 7a18 second prototype 1.jpg | Second prototype of 7A18
Tek 7a18 second prototype 2.jpg | Second prototype of 7A18
Third prototype of 7a18 1.jpg  | Third prototype of 7A18
Third prototype of 7a18 2.jpg  | Third prototype of 7A18
Third prototype of 7a18 3.jpg  | Third prototype of 7A18
</gallery>
 
===7A18A===
<gallery>
Tek-7a18a-front.jpg                | 7A18A Front
7a18a-left.jpg                      | 7A18A left side.  The step attenuators can be seen on the left, the amplifier board on the right.
7a18a-right.jpg                    | 7A18A right side.  The circuit boards on top carry the readout circuitry.
</gallery>
 
'''Option 06'''
<gallery>
Tek-7a18a-opt06-front.jpg  | 7A18A Opt.06 Front. AC/GND/DC switches have an extra rightmost "DC Offset" position enabling the offset controls.
Tek-7a18a-opt06-left.jpg  | 7A18A Opt.06 left side (rear).  Note the two blue 10T-potentiometers for offset voltage adjustment.
Tek-7a18a-opt06-offset.jpg | 7A18A Opt.06 - offset controls take the place of the Identify buttons on the standard model.
</gallery>
 
==Components==
{{Parts|7A18}}
 
{{Parts|7A18A}}
 
 
[[Category:7000 series vertical plugins]]
Gregor
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