ET4331 Transmitter High Power Communications

Circuit Diagram, Service Manual, Service Information,  Schematic Diagrams and Manuals

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ET4331 High Power Communications Transmitter.


Frequency Range 3000 to 20,000 KC

Power Output
Telegraph 1300 watts
Telephone 1000 watts

Power Input
Telegraph (Max.) 4150 watts
Telephone (Max.) 5400 watts
Power Supply 1 ph. 220 v. 50/60 cycles

Tube Complement
Crystal Oscillator I RCA-802
Intermediate Power Amplifier 1 RCA-803

ET 4331 1.jpg (64054 bytes)

Power Amplifier 2 RCA-833-A
1st Audio Amplifier 1 RCA-5 3
2nd Audio Amplifier 4 RCA-2A3
Modulator 2 RCA-833-A
Rectifier 4 RCA-8 72-A/8 72

Height (Overall) 84½ inches
Length 361,4 inches
Depth (Overall) 27% 6 inches
Weight 1635 pounds

The H-F Communications Transmitters described  
are identified by the Ml designations, MI-7 162 and MI-7 162-A. The MI-7 162 is less the coupling unit, while the MI-7 
162-A is including the coupling unit. In all 
other respects, the equipments are identical.

ET 4331 5.jpg (74698 bytes)


Output Frequency 2 to 20 megacycles
Output Level, Buffer-Amplifier Sufficient to drive an RCA-80 7
Modulation Frequency 600 cycles
Frequency Deviation (maximum) ±500 cycles
Power Consumption 200 watts
Power Supply 11 5/2 30 volts, 50/60 cycles
Oscillator Filament Current 0.05 ampere d.c.
Amplifier and Tone Generator Filament 
Voltage 6.3 volts a.c.

Electron-Coupled Oscillator 2 RCA-3Q5-GT
Buffer-Amplifier 1 RCA-807
Tone Generator I RCA-6AB7, 1 RCA-6F6

Regulated Power Supply
2 RCA-5U4-G, 5 RCA-6Y6-G,
I. I RCA-1852, 2 RCA-VR-150/30

ET 4331 3.jpg (54054 bytes)

Dimensions Height, 66 9/16 in.; Width, 22 in.; Depth, 17 1/8 in.
Weight 275 pounds

Frequency Change
Line voltage change, ± 10 per cent  0.000 5 per cent
Temperature change, per degree Fahrenheit  0.000 7 per cent
Relative humidity change of 1 per cent  over the range of 30 to 95 at a dry bulb temperature of 110 degrees F  0.000 3 per cent
Drift from cold start, first reading taken within 1  minute after applying power:
Frequency deviation at the end of the first  hour a negative drift of 100-400 cycles (measured at 7 mc)

The Master Oscillator Equipment is  identified by the stock number MI- 19427-B and is  composed of the following major items:
1 Master Oscillator Unit (K-882006)
I Transmission Line Cable, 50 feet long (K-881380-1)
I Instruction Book IB-300 14-1

ET 4331 4.jpg (53918 bytes)

The Manual is complete except for the Oscillator regulated power supply circuit

The Manual contains the following :-

1 - Type ET-4 331 High-Frequency Transmitter 
2 - Transmitter. (Rear View)
3 - Transmitter (Side Elevations)
4 - Transmitter (Schematic T-61 1 5 11)
5 - Transmitter (Connections TT-6 1 1654)
6 - Transmitter Coupling Unit (Connections M-429639) 
7 - Transmitter (Outline M-4 18357) 
8 - Crystal Oscillator (Dial B) (Calibration Curve S-85 1196)
9 - Intermediate Power Amplifier (Dial C) (Calibration Curve 5-851197)
40 - Power Amplifier (Dial F) (Calibration Curve 5-851198)

Electrical Characteristics
Tube Complement
Mechanical Specifications
Typical Performance Data



Frequency Stability


1 - MI-I 942 7-B Master Oscillator (Front Oblique View, Access Covers in Place)

2 - Oscillator Controls “B” and “C” (Typical Calibration, S-852928—Sub 0) 

3 - Oscillator Controls “D” and “E” (Typical Calibration, S-85292 7—Sub 0)

4 - Oscillator Controls “F” and “Output Circuit” (Typical Calibration, S-852926----Sub 0)

5 - MI-1 942 7-B Master Oscillator (Front Oblique View, Access Covers Removed)

6 - MI- 19427-B Master Oscillator (Rear View, Access Door Open)

7 - Master Oscillator Chassis (Top View)

8 - Master Oscillator Chassis (Bottom View)

9 - Tone Generator Unit (Front View)

10 - Tone Generator Chassis (Bottom View)

I 1 - Regulated Power Supply Unit (Rear View)

12 - Master Oscillator Unit (Schematic, P-722222-Sub 1)

13 - Tone Generator Unit (Schematic, M-426986-Sub 2) 

14 - Regulated Power Supply Unit (Schematic, P-72 199O-Sub 1) N/A

Manual and Circuit
available Details Below
As a Download

Click Here

The Manual is complete except for the Oscillator regulated power supply circuit

ET4331 Transmitter High Power Communications
Manuals are Available Worldwide as a Download.

Manual including circuits 50 pages

Manual 50 A4 pages worldwide

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We do all we can to provide the very best that is available for you.
But in the unlikely event that any data should not be as you expected.
A refund is always available. Kind Regards Allen and Alanna.

Manuals are Available Worldwide as a Download

Thank you for your interest. Allen and Alanna G0RIT
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Revised: February 09, 2021