3A74: Difference between revisions

Revision as of 23:56, 28 November 2023

Tektronix 3A74
2 MHz four channel vertical amp 3A74 front Compatible with 560-series scopes Produced from 1962 to 1974 Manuals Tektronix 3A74 Manual (PDF) / @ BAMA (DjVu) Tektronix 3A74 Factory Calibration Procedure, July 1969‎ Tektronix 3A74 Calibration Outline (PDF, OCR) (All manuals in PDF format unless noted otherwise)

Manuals – Specifications – Links – Pictures

The Tektronix 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

US-Made Version

Front Side
Rear Side
Left Side
Right Side
Block Diagram
Channel Switching
Amplifier
VAR GAIN potentiometer, sometimes problematic
3A74 Engine Analyzer Amplifier

Netherlands-Made Version

Some Parts Used in the 3A74

Part	Part Number(s)	Class	Description	Used in
6CL6	154-031 • 154-0031-00 • 154-0286-00	Vacuum Tube (Pentode)	7.5 W power pentode	132 • 310 • 310A • 316 • 317 • 515 • 524 • 525 • 531 • 535 • 535A • 545 • 545A • 545B • 549 • 570 • 581 • 581A • 585 • 585A • 3A74
7586	154-0306-00	Vacuum Tube (Triode)	Nuvistor triode	M • 1A1 • 1A2 • 1A5 • 10A2 • 10A2A • 11B1 • 11B2A • 321 • 321A • 3A1 • 3A1S • 3A3 • 3A5 • 3A6 • 3A7 • 3A8 • 3A74 • 3S76 • 3T77 • 3T77A • 3B5 • 4S1 • 4S2 • 6R1 • 6R1A • 9A1 • 9A2 • 82 • 86 • S-311

@@ Line 13: / Line 13: @@
 * [[Media:Tek 3a74 cal outline.pdf|Tektronix 3A74 Calibration Outline (PDF, OCR)]]
 }}
-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.
+The '''Tektronix 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.
@@ Line 46: / Line 46: @@
 ==Pictures==
-===US-made Version===
+'''US-Made Version'''
 <gallery>
 Tek_3A74_front.jpg
@@ Line 70: / Line 70: @@
 Tek 3a74 engine analyzer amplifier.jpg|3A74 Engine Analyzer Amplifier
 </gallery>
-===Netherlands-made Version===
+'''Netherlands-Made Version'''
 <gallery>
 Tek 3a74 nl1.jpg