Emerson 645 Audio Schematics Instruction Manual
- June 1, 2024
- Emerson
Table of Contents
Emerson 645 Audio Schematics
Emerson Radio
MODEL: 645
CHASSIS MODEL: 120115′
This document provides the schematic diagram for the Emerson Radio Model 645. The diagram includes various electronic components such as resistors, capacitors, tubes, and transformers, each represented by standard electronic symbols. The diagram is laid out to show the electrical connections and signal path through the radio.
On the right side of the diagram, there are insets that provide additional details:
- A pointer and dial cord drive illustration showing the front and back orientations for the tuning mechanism.
- Close-up views of tube socket pin arrangements for tubes 35A5, 12J5, 12SA7, 12SK7, 12SQ7, and 50L6.
- An illustration of a condenser with a note indicating “2 1/2 TURNS” and “CONDENSER FULLY CLOSED”.
Below the radio schematic, there’s a section titled “CONDITIONS FOR VOLTAGE AND RESISTANCE READINGS” which specifies the test conditions needed to measure voltages and resistances accurately:
- All voltage readings are peak-to-peak values unless otherwise specified.
- Set volume control at maximum resistance (fully clockwise).
- Band switch position at broadcast.
- The line voltage is assumed to be 117 volts AC.
- Resistance measurements are made with a 20,000 ohms-per-volt meter or equivalent.
- The negative meter lead is connected to the chassis (except where noted).
Specifications
| Tube Type | Function |
|---|---|
| 35A5 | Output Amplifier |
| 12J5 | Oscillator |
| 12SA7 | Mixer |
| 12SK7 | IF Amplifier |
| 12SQ7 | Detector |
| 50L6 | Rectifier |
DIAGRAM
CONDITIONS FOR VOLTAGE AND RESISTANCE READINGS
- Voltage readings are + dc. volts, resistance readings are obms unless otherwise noted.
- All measurements made with voltohmyst or equivalent.
- Socket connections are shown as bottom views, with valves measured from socket pin to chassis.
- No signal applied for voltage measurements.
- Nominal tolerance on component valves makes possible a variation of $ 15c, in readings.
- Me Ge velage and resistance diagram, readings above line are voltage, valves below line indicate resistance. K=- kilohms.
- Valves marked * measured to pin 4 of V-4 (B+).
FAQ
What is the significance of the 2 1/2 TURNS note on the condenser?
This indicates the position at which the condenser is fully closed, which may be relevant for tuning or repair purposes.
How should the volume control be set for taking voltage and resistance readings?
The volume control should be set to the maximum resistance, which means turning it fully clockwise.
What is the line voltage assumed for the voltage readings specified in the manual?
The readings are based on an assumed line voltage of 117 volts AC.
Why is the negative meter lead connected to the chassis?
This is a common ground reference point for taking measurements unless otherwise noted in specific test conditions. The document concludes with the page number 49 at the bottom, indicating its sequence in the manual.
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