Elenco Electronics AM-550K Assembly And Instruction Manual
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Elenco Electronics AM-550K Assembly And Instruction Manual

Elenco Electronics AM-550K Assembly And Instruction Manual

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AM RADIO KIT
MODEL AM-550K
INTEGRAL CIRCUIT, 3 TRANSISTORS, DIODE
Assembly and Instruction Manual
Elenco
®
Electronics, Inc.
Copyright © 2007, 1999 Elenco
®
Electronics, Inc.
Revised 2007
REV-S
752550
No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.

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  • Page 1 AM RADIO KIT MODEL AM-550K INTEGRAL CIRCUIT, 3 TRANSISTORS, DIODE Assembly and Instruction Manual Elenco ® Electronics, Inc. Copyright © 2007, 1999 Elenco ® Electronics, Inc. Revised 2007 REV-S 752550 No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.

  • Page 2: Parts List

    PARTS LIST If you are a student, and any parts are missing or damaged, please see instructor or bookstore. If you purchased this kit from a distributor, catalog, etc., please contact Elenco mail is at the back of this manual) for additional assistance, if needed. DO NOT contact your place of purchase as they will not be able to help you.

  • Page 3: Parts Identification

    PARTS IDENTIFICATION RESISTORS CAPACITORS SEMICONDUCTORS Diode Resistor 50kΩ Potentiometer with Switch Discap Electrolytic Tuning Radial LM-386 IC Transistor COILS Color Dot Plastic Holders Coil Ferrite Core Coil Antenna Assembly MISCELLANEOUS Screw M2.5 x 3.8mm 2-56 Screw Screw 2-56 x 1/4” 2-56 x 5/16”...
  • Page 4 IDENTIFYING RESISTOR VALUES Use the following information as a guide in properly identifying the value of resistors. BAND 1 BAND 2 1st Digit 2nd Digit Color Digit Color Digit Black Black Brown Brown Orange Orange Yellow Yellow Green Green Blue Blue Violet Violet...

  • Page 5: General Discussion

    INTRODUCTION The Elenco ® Superhet 550 AM Radio Kit is a “superheterodyne” receiver of the standard AM (amplitude modulation) broadcast frequencies. The unique design of the Superhet 550 allows you to place the parts over their corresponding symbol in the schematic drawing on the surface of the printed circuit board during assembly.
  • Page 6 CONSTRUCTION Introduction Assembly of your AM-550 AM Radio Kit will prove to be an exciting project and give you much satisfaction and personal achievement. If you have experience in soldering and wiring techniques, then you should have no problem with the assembly of this kit. Care must be given to identifying the proper components and in good soldering habits.
  • Page 7 A poorly soldered joint can greatly affect small current flow in circuits and can cause equipment failure. You can damage a PC board or a component with too much heat or cause a cold solder joint with insufficient heat. Sloppy soldering can cause bridges between two adjacent foils preventing the circuit from functioning. What Good Soldering Looks Like A good solder connection should be bright, shiny, smooth, and uniformly flowed over all surfaces.
  • Page 8 SEMICONDUCTOR PARTS FAMILIARIZATION This section will familiarize you with the proper method used to test the transistors and the diode. TRANSISTOR TEST Refer to the parts list and find transistors. These are NPN transistors. Refer to Test A for locating the Emitter, Base and Collector.

  • Page 9: Audio Amplifier

    AUDIO AMPLIFIER The purpose of the Audio Amplifier is to increase the audio power to a level sufficient to drive an 8 ohm speaker. To do this, DC (direct current) from the battery is converted by the amplifier to an AC (alternating current) in the speaker. The ratio of the power delivered to the speaker and the power taken from the battery is the efficiency of the amplifier.

  • Page 10: Assembly Instructions

    ASSEMBLY INSTRUCTIONS We will begin by installing the speaker. Be careful to properly mount and solder all components. Diodes and electrolytic capacitors are polarized, be sure to follow the instructions carefully so that they are not mounted backwards. Check the box when you have completed each installation. Figure B If the speaker pad has center and outside pieces, then remove them.
  • Page 11 ASSEMBLY INSTRUCTIONS TP6 - Test Point Pin (see Figure E) C12 - 10μF Lytic Capacitor (see Figure F) C11 - 10μF Lytic Capacitor (see Figure F) R13 - 47Ω 5% 1/4W Resistor (yellow-violet-black-gold) U1 - IC Socket 8-Pin U1 - Integrated Circuit LM-386 (see Figure I) Pot with Switch Nut &...

  • Page 12: Power Up Test

    You have completed wiring the Audio Amplifier. We shall proceed in testing this circuit. You will need for static measurements, a Volt-Ohm-Milliammeter, preferably a digital type. STATIC MEASUREMENTS RESISTANCE TEST Adjust the Volt-Ohm-Milliammeter (VOM) to the highest resistance scale available. Connect the VOM to pin 6 of the IC as shown in Figure 6.
  • Page 13 OUTPUT BIAS TEST Adjust your VOM to read 9 volts and connect it to test point 7 (TP7) as shown in Figure 8. Make sure that the battery, or a 9 volt power supply (if available), is properly connected and turn the power ON. The voltage at TP7 should be between 4 to 6 volts.
  • Page 14 DYNAMIC MEASUREMENTS AC BANDWIDTH Connect the oscilloscope and audio generator to your circuit as shown in Figure 10. Set the audio generator for a frequency of 1kHz and minimum voltage output. Set the oscilloscope to read .5 volts per division. Turn the power ON and slowly increase the generator output until the oscilloscope displays 2 volts peak to peak (Vpp) at TP7.
  • Page 15 DISTORTION Connect the generator and oscilloscope as shown in Figure 10. Set the generator at a frequency of 1kHz, turn the power ON and adjust the generator output Clipped Measure the maximum voltage peak to peak when clipping first occurs and record that value here: Vclp = _______ Vpp.
  • Page 16 AM DETECTOR AND AGC STAGES THEORY OF OPERATION The purpose of the detector is to change the amplitude modulated IF signal back to an audio signal. This is accomplished by a process called detection or demodulation. modulated IF signal is applied to a diode in such a way as to leave only the negative portion of that signal (see Figure 13).
  • Page 17 ASSEMBLY INSTRUCTIONS - AM DETECTOR AND AGC STAGES C6 - 100μF Lytic Capacitor (see Figure F) R5 - 27kΩ 5% 1/4W Resistor (red-violet-orange-gold) T1 - IF Coil (Yellow Dot) TP3 - Test Point Pin (see Figure E) R11 - 3.3kΩ Resistor (orange-orange-red-gold) C4 - 10μF Lytic Capacitor (see Figure F)

  • Page 18: System Check

    DYNAMIC MEASUREMENTS DETECTOR AND ACG TEST Turn the power OFF and connect the VOM and RF generator as shown in Figure 15. Set the VOM to accurately read 2 volts DC and set the output of the RF generator for 455kHz, no modulation, and minimum amplitude.
  • Page 19 SECOND IF AMPLIFIER THEORY OF OPERATION The purpose of the SECOND IF AMPLIFIER is to increase the amplitude of the intermediate frequency (IF) and at the same time provide SELECTIVITY. Selectivity is the ability to “pick out” one radio station while rejecting all others.
  • Page 20 STATIC MEASUREMENTS Q3 BIAS With the power OFF, connect the negative lead of your VOM to any ground and the positive lead to the emitter of Q3 as shown in Figure 18. Set the VOM to read 9 volts DC and turn ON the power. The voltage at the Figure 18 If you do not have an RF generator or oscilloscope, skip the following test and go to Section 4.

  • Page 21: Bandwidth Test

    BANDWIDTH TEST With the power OFF, connect your equipment as shown in Figure 20. Turn the power ON and adjust the RF generator for .4Vpp at the cathode of D1. If necessary, realign transformer T3 for maximum output while adjusting the output of the RF generator to maintain .4Vpp.
  • Page 22 STATIC MEASUREMENTS Q2 BASE BIAS With the power turned OFF, reconnect your VOM to test point 3 (TP3) as shown in Figure 14. Set the VOM to read 2 volts DC accurately and turn the power ON. The Q2 CURRENT With the power turned OFF, connect the positive lead of the VOM to the emitter of Q2.
  • Page 23 MIXER AND OSCILLATOR THEORY OF OPERATION In a superheterodyne type receiver the radio wave at the antenna is amplified and then mixed with the local oscillator to produce the intermediate frequency (IF). Transistor Q1 not only amplifies the RF signal but also simultaneously oscillates at a frequency 455kHz above the desired radio station frequency.
  • Page 24 ASSEMBLY INSTRUCTIONS - ANTENNA, MIXER AND OSCILLATOR L1 - Antenna (see Figure K) C2 - .02μF Discap (203) or .022μF Discap (223) TP1 - Test Point Pin (see Figure E) R2 - 12kΩ Resistor (brown-red-orange-gold) R3 - 3.3kΩ Resistor (orange-orange-red-gold) Tuning Capacitor Your kit may contain a 3 lead or a 4 lead capacitor.
  • Page 25 IMPORTANT: Before installing the antenna coil, determine if you have a 3 wire coil or a 4 wire coil. Assemble it to the PC board as shown below. Mount the antenna assembly to the PC board. Put the tab of the first holder into the right hole and twist the tab 90 Put the tab of the second holder into the left hole and twist the tab 90 Slide the ferrite core through the holders.
  • Page 26 STATIC MEASUREMENTS Q1 BIAS With the power turned OFF, connect the VOM to your circuit as shown in Figure 22. Connect a clip lead from test point two (TP2) to the collector of Q1. This short prevents Q1 from oscillating. Set the VOM to read 2 volts DC accurately and turn the power ON.
  • Page 27 FINAL ALIGNMENTS IF BANDWIDTH With the power turned OFF, connect the RF generator and the oscilloscope to your circuit as shown in Figure 24. Short TP2 to the collector of Q1 with a clip lead to “kill” the local oscillator. Set the RF generator at a frequency of 455kHz, modulation of 400Hz 80%, minimum amplitude output.

  • Page 28: Antenna Alignment

    After peaking the oscillator trimmer capacitor, return the RF generator to 540kHz, and capacitor C1 to the fully counter-clockwise position and readjust L2. Repeat the last few steps until both settings of the oscillator are correct. This process sets the oscillator range at 995kHz to 2055kHz.
  • Page 29 FINAL ALIGNMENT WITH NO TEST EQUIPMENT It is best to use an earphone for this alignment procedure. With an alignment tool or screwdriver, turn coils L2, T1, T2 and T3 fully counter-clockwise until they stop. DO NOT FORCE THE COILS ANY FURTHER. Turn each coil in about 1 1/4 to 1 1/2 turns.
  • Page 30 The final step in the radio kit will be to assemble and attach a baffle to the speaker. You will need to remove the baffle located in the bottom of the box. If it does not want to come out easily, use a knife to cut the holding tabs.

  • Page 31: Schematic Diagram

    SCHEMATIC DIAGRAM -30-...
  • Page 32 Elenco ® Electronics, Inc. 150 Carpenter Avenue Wheeling, IL 60090 (847) 541-3800 Web site: www.elenco.com e-mail: elenco@elenco.com...

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