3A74: Difference between revisions

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The Tektronix Type 3A74 is a four-channel vertical plug-in [[introduced in 1963]] for
{{Plugin Sidebar 2|
[[560-series scopes]].  The bandpass is DC to 2 MHz.  Each input signal passes through
title=Tektronix 3A74|
switchable input attenuators and then into a cathode-follower made from a [[7586]]
summary=2 MHz four channel vertical amp|
Nuvistor triode.  That drives a PNP differential amplifier.  The output of this
image=Tek_3A74_front_crop.jpg |
caption=3A74 front|
introduced=1962 |
discontinued=1974 |
series=[[560-series scopes]]|
manuals=
* [http://bama.edebris.com/download/tek/3a74/3a74.djvu Tektronix 3A74 Manual (DjVu)]
}}
The '''Tektronix Type 3A74''' is a four-channel vertical plug-in [[introduced in 1963]] for
[[560-series scopes]].  The bandwidth is DC to 2 MHz.   
 
A modified 3A74 MOD 730A (with a charge pre-amplifier on channel 1 to accommodate piezoelectric pressure transducers)
was part of the [[Engine Analyzer]] package.
 
{{BeginSpecs}}
{{Spec | Bandwidth | 2 MHz}}
{{Spec | Input impedance | 1 MΩ // 47 pF }}
{{Spec | Deflection | 20 mV/Div to 10 V/Div in 1–2–5 sequence }}
{{Spec | Features |
* Invert switch per channel
}}
{{EndSpecs}}
 
==Internals==
Each input signal passes through switchable input attenuators and then into a cathode-follower  
made from a [[7586]] Nuvistor triode driving a PNP differential amplifier.  The output of this
differential amplifier, for each of the four channels, passes through a diode-based
differential amplifier, for each of the four channels, passes through a diode-based
analog signal switching network (multiplexer).  The output of that multiplexer drives the output amplifier,
analog signal switching network (multiplexer).  The output of that multiplexer drives the output amplifier,
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This allows each of the input signals to be traced on the screen, one after another.
This allows each of the input signals to be traced on the screen, one after another.


* [http://bama.edebris.com/download/tek/3a74/3a74.djvu Tektronix 3A74 Manual (DjVu)]
The 3A74 uses Tek-made 185 Ω [[potentiometers]] in for the VAR GAIN controls.
These can be a [[:Category:Repair_issues|maintenance issue]].
 
The 3A74 contains a total of eight 7586 [[Nuvistor]]s.
 
==Links==
* [http://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_other/3A74.htm Tek 3A74 @ amplifier.cd]
* [http://www.barrytech.com/tektronix/vintage/tek3a74.html Tek 3A74 @ barrytech.com]
* [https://www.radiomuseum.org/r/tektronix_3a74_plug_in_unit.html Tek 3A74 @ radiomuseum.org]
 
==Pictures==
<gallery>
Tek_3A74_front.jpg
Tek 3a74 1.JPG|Front Side
Tek 3a74 2.JPG|Rear Side
Tek 3a74 3.JPG|Left Side
Tek 3a74 4.JPG|Right Side
3a74 block diagram.png|Block Diagram
3a74 switching.png|Channel Switching
3a74 amp schem.png|Amplifier
Tek 311-0304-00 pot.jpg|VAR GAIN potentiometer, sometimes problematic
Tek 3a74 s1.jpg
Tek 3a74 s2.jpg
Tek 3a74 s3.jpg
Tek 3a74 s4.jpg
Tek 3a74 s5.jpg
Tek 3a74 front.jpg
Tek 3a74 right.jpg
Tek 3a74 left.jpg
Tek 3a74 top.jpg
Tek 3a74 bottom.jpg
Tek 3a74 rear.jpg
</gallery>
 
 
[[Category:560 series plugins]]

Revision as of 10:20, 12 December 2018

Template:Plugin Sidebar 2 The Tektronix Type 3A74 is a four-channel vertical plug-in introduced in 1963 for 560-series scopes. The bandwidth is DC to 2 MHz.

A modified 3A74 MOD 730A (with a charge pre-amplifier on channel 1 to accommodate piezoelectric pressure transducers) was part of the Engine Analyzer package.

Key Specifications

Bandwidth 2 MHz
Input impedance 1 MΩ // 47 pF
Deflection 20 mV/Div to 10 V/Div in 1–2–5 sequence
Features
  • Invert switch per channel

Internals

Each input signal passes through switchable input attenuators and then into a cathode-follower made from a 7586 Nuvistor triode driving a PNP differential amplifier. The output of this differential amplifier, for each of the four channels, passes through a diode-based analog signal switching network (multiplexer). The output of that multiplexer drives the output amplifier, which is part transistor, part tube. The one-hot select line signals for the multiplexer are generated by a transistor-based ring oscillator, a four-state cyclic state machine. This allows each of the input signals to be traced on the screen, one after another.

The 3A74 uses Tek-made 185 Ω potentiometers in for the VAR GAIN controls. These can be a maintenance issue.

The 3A74 contains a total of eight 7586 Nuvistors.

Links

Pictures