3A74: Difference between revisions

Revision as of 12:28, 16 November 2014

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	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. 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

Front Side
Rear Side
Left Side
Right Side
Block Diagram
Channel Switching
Amplifier
VAR GAIN potentiometer, sometimes problematic

@@ Line 32: / Line 32: @@
 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==
 * [http://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_other/3A74.htm Tek 3A74 page @ amplifier.cd]
@@ Line 45: / Line 47: @@
 File:3a74 switching.png|Channel Switching
 File:3a74 amp schem.png|Amplifier
+File:Tek 311-0304-00 pot.jpg|VAR GAIN potentiometer, sometimes problematic
 </gallery>
 [[Category:560 series plugins]]