Signal Electronics, Inc. AF252 Schematic

Signal Electronics, Inc. AF252

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Product Information:
Model:AF252
Manufacturer:Signal Electronics, Inc.

Schematics Content

Page 2:

Lack of sensitivity and poor tone quality may be due to any one or ? combination of causes such as weak or defective tubes or speaker, open resistors or shorted condensers, etc. DO NOT ATTEMPT TO REALIGN THIS RECEIVER UNTIL ALL OTHER POSSIBLE SOURCES OF TROUBLE HAVE BEEN FIRST THOROUGHLY INVESTIGATED AND DEFINITELY PROVED NOT TO BE THE CAUSE.

EQUIPMENT NECESSARY

ALIGNMENT PROCEDURE

1. Signal generator-accurately calibrated that will cover the following frequencies:
AM BAND 455 KC, 1400 KC, 1620 KC.
FM BAND 21.75 MC, 88 MC, 103 MC, 108 MC.

2. Output indicator; to be connected across the voice coil or primary of the output transformer.

BROADCAST BAND ALIGNMENT - (AM)

1. Set signal generator at 455 KC. Receiver variable condenser plates completely unmeshed.
2. Connect generator to grid of converter tube through a. 1 mfd. condenser.
3. Adjust trimmers T1, T2, T3, and T4 in order for maximum output.
4. Connect generator to external antenna lead on loop.
5. Set generator at 1620 KC. Receiver variable condenser completely unmeshed,
6. Adjust oscillator trimmer T5 for maximum output.
7. Set generator and receiver at 1400 KC.
8. Adjust RF trimmer T6 for maximum output.

FREQUENCY MODULATION BAND ALIGNMENT (FM)

NOTES: The average noise output of this receiver, when no FM signal is present is approximately 150 milliwatts in 3.2 ohms (4 volts across 3.2 ohms). The output meter range should be set accordingly.

1. Set generator at 21.75 MC, with modulation off.
2. Couple generator to RF grid (pin # 8) of 14F8 through a 2 mmfd. condenser.
3. Adjust T7 on IF can for minimum output.
4. Remove jumper between terminals A2 and A3 on loop and connect generator to terminals Al and A2 through a 300 ohm resistor, ground lead of generator to Al.
5. Set RF trimmer T9 to 1/2 capacity, (lettering on the trimmer should be at right angles to its length.)
6. Turn receiver dial to the market on the extreme right side of the dial back. This corresponds to 108 mc.
7. Set generator at 108 mc.
8. Adjust oscillator trimmer T8 for minimum output.
9. Set generator at 88 mc.
10. Set receiver dial to second marker from the extreme left side of the dial back. This corresponds to 88 mc.
11. Adjust oscillator coil for minimum output. Squeeze turns together to bring frequency lower, separate turns to bring frequency higher. Care must be exercised in this adjustment as a slight movement of the turns of the coil will change the frequency of the oscillator a few magacycles, Make certain that the turns do not touch each other.
12. Repeat steps 6 to 11 inclusive as the adjustment at 88 mc. will affect the adjustment at 108 mc and vice versa.
13. Set generator at 103 mc.
14. Tune receiver to 103 mc.
15. Adjust RF trimmer T9 for minimum output while rocking the variable condenser.