3A74: Difference between revisions
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The 3A74 uses Tek-made 185-ohm [[potentiometers]] in for the VAR GAIN controls. | The 3A74 uses Tek-made 185-ohm [[potentiometers]] in for the VAR GAIN controls. | ||
These can be a [[ | These can be a [[:Category:Repair_issues|maintenance issue]]. | ||
==Links== | ==Links== | ||
* [http://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_other/3A74.htm Tek 3A74 page @ amplifier.cd] | * [http://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_other/3A74.htm Tek 3A74 page @ amplifier.cd] | ||
Revision as of 14:05, 15 June 2015
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.
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 |
|
Internals
Each input signal passes through switchable input attenuators and then into a cathode-follower made from a 7586 Nuvistor triode. That drives 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-ohm potentiometers in for the VAR GAIN controls. These can be a maintenance issue.
Links
Pictures
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Front Side
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Rear Side
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Left Side
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Right Side
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Block Diagram
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Channel Switching
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Amplifier
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VAR GAIN potentiometer, sometimes problematic
