Elenco Electronics SUPERHET AM-550TK Assembly And Instruction Manual
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Elenco Electronics SUPERHET AM-550TK Assembly And Instruction Manual

Elenco Electronics SUPERHET AM-550TK Assembly And Instruction Manual

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AM RADIO KIT
MODEL
SUPERHET AM-550TK
7 TRANSISTORS
Assembly and Instruction Manual
Elenco
Electronics, Inc.
TM
Copyright © 2003, 1999 Elenco
TM
Electronics, Inc.
Revised 2003
REV-D
752550T

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Summary of Contents for Elenco Electronics SUPERHET AM-550TK

  • Page 1 AM RADIO KIT MODEL SUPERHET AM-550TK 7 TRANSISTORS Assembly and Instruction Manual Elenco Electronics, Inc. Copyright © 2003, 1999 Elenco Electronics, Inc. Revised 2003 REV-D 752550T...

  • Page 2: Parts List

    If you are a student, and any parts are missing or damaged, please see instructor or bookstore. If you purchased this AM radio kit from a distributor, catalog, etc., please contact Elenco (address/phone/e-mail is at the back of this manual) for additional assistance, if needed.

  • Page 3: Parts Identification

    PARTS IDENTIFICATION RESISTORS Resistor 50kW Potentiometer/ Switch with Nut and Washer Color Dot Coil Knob (dial) Screw M2.5 2-56 x 1/4” Speaker CAPACITORS Discap Electrolytic Tuning Radial COILS Antenna Assembly MISCELLANEOUS Knob (pot) 2-56 Screw Earphone Jack with Nut Speaker Pad Label SEMICONDUCTORS Diode...
  • Page 4 IDENTIFYING RESISTOR VALUES Use the following information as a guide in properly identifying the value of resistors. BAND 1 1st Digit Color Digit Black Brown Orange Yellow Green Blue Violet Gray White IDENTIFYING CAPACITOR VALUES Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or mF (microfarads). Most capacitors will have their actual value printed on them.

  • Page 5: General Discussion

    INTRODUCTION The Elenco Superhet 550T AM Radio is a “superheterodyne” receiver of the standard AM (amplitude modulated) broadcast frequencies. The unique design of the Superhet 550T allows you to place the parts over its corresponding symbol in the schematic drawing on the surface of the printed circuit board during assembly.
  • Page 6 CONSTRUCTION Introduction The most important factor in assembling your Elenco Superhet 550T AM Transistor Radio Kit is good soldering techniques. Using the proper soldering iron is of prime importance. A small pencil type soldering iron of 25 - 40 watts is recommended. The tip of the iron must be kept clean at all times and well tinned.
  • Page 7 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 a NPN transistor. Refer the Figure C (page 8) for locating the Emitter, Base and Collector.

  • Page 8: Audio Amplifier

    AUDIO AMPLIFIER Theory of Operation - 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.
  • Page 9 ASSEMBLY INSTRUCTIONS - AUDIO AMPLIFIER We will begin by installing resistor R14. Identify the resistor by its color code and install as shown on page 3. Be careful to properly mount and solder all components. Diodes, transistors and electrolytic capacitors are polarized, be sure to follow the instructions carefully so that they are not mounted backwards.

  • Page 10: Assembly Instructions

    ASSEMBLY INSTRUCTIONS Figure G Step 1: If the speaker pad has center and outside pieces, then remove them. Peel the backing off of one side of the speaker pad and stick the pad onto the speaker. Step 2: Remove the other backing from the speaker pad.

  • Page 11: Static Measurements

    You have completed wiring the Audio Amplifier. We shall proceed in testing this circuit. You will need 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 the circuit as shown in Figure 3.

  • Page 12: Input Bias

    OUTPUT BIAS TEST Adjust your VOM to read 9 volts and connect it to test point 8 (TP8) as shown in Figure 5. Make sure that the battery, or a 9 volt power supply (if available), is properly connected and turn the power ON.
  • Page 13 DYNAMIC MEASUREMENTS DC GAIN Adjust your VOM to read 9 volts DC. Connect the positive lead of the VOM to TP6 and the negative lead to any ground. Turn the power ON and record the voltage at TP6 here: V1=________ volts. Place resistor R4 across resistor R13 as shown in Figure 6.
  • Page 14 AC GAIN Connect the VOM and generator to TP6 as shown in Figure 7. Turn the power ON. Normally the AC gain is measured at a frequency of 1 kilohertz (kHz). Your VOM, however, may not be able to accurately read AC voltages at this frequency.
  • Page 15 AC BANDWIDTH Connect the oscilloscope and generator to your circuit as shown in Figure 8. Set the 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 TP8.
  • Page 16 DISTORTION Connect the generator and oscilloscope as shown in Figure 8. Set the generator at a frequency of 1kHz, turn the power ON and adjust the generator output until the Clipped Measure the maximum voltage peak to peak when clipping first occurs and record that value here: Vclp = _______ Vpp.
  • Page 17 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. First, the amplitude modulated IF signal is applied to a diode in such a way as to leave only the negative portion of that signal (see Figure 11).
  • Page 18 ASSEMBLY INSTRUCTIONS - DETECTOR C6 - 100mF Lytic (see Figure B) R5 - 27kW Resistor (red-violet-orange-gold) T1 - IF Coil (yellow) TP3 - Test Point Pin (see Figure A) C4 - 10mF Lytic (see Figure B) R11 - 3.3kW Resistor (orange-orange-red-gold) C9 - .02mF or .022mF Discap (marked 203 or 223)

  • Page 19: Dynamic Measurements

    DYNAMIC MEASUREMENTS DETECTOR AND ACG TEST Turn the power OFF and connect the VOM and RF generator as shown in Figure 13. accurately read 2 volts DC and set the output of the RF generator for 455kHz, no modulaton, and minimum amplitude.
  • Page 20 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 21 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 16. Set the VOM to read 9 volts DC and turn ON the power. The voltage at the Amps COM Figure 16 If you do not have an RF generator or oscilloscope, skip the following test and go to Section 4.

  • Page 22: Bandwidth Test

    BANDWIDTH TEST With the power OFF, connect your equipment as shown in Figure 17A. 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 23 STATIC MEASUREMENTS Q2 BASE BIAS With the power turned OFF, reconnect your VOM to test point 3 (TP3) as shown in Figure 12. Set the VOM to read 2 volts DC accurately and turn the power ON. The voltage Q2 CURRENT With the power turned OFF, connect the positive lead of the VOM to the emitter of Q2.
  • Page 24 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 25 ASSEMBLY INSTRUCTIONS - ANTENNA, MIXER AND OSCILLATOR L1 - Antenna with Holders (see Figures I & J) C2 - .02mF or .022mF Discap (marked 203 or 223) TP1 - Test Point Pin (see Figure A) R2 - 12kW Resistor (brown-red-orange-gold) R3 - 3.3kW Resistor (orange-orange-red-gold) Figure I...
  • Page 26 Your kit may contain a 3 lead or a 4 lead capacitor. Bend the leads as shown. Fasten C1 into place on the top side of the PC board with two M2.5 screws. Knob Post Screw Holes Solder leads to pads Punch out one antenna shim from the front flap of the box.

  • Page 27: Oscillator Circuit

    STATIC MEASUREMENTS Q1 BIAS With the power turned OFF, connect the VOM to your circuit as shown in Figure 19. 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 28 FINAL ALIGNMENTS IF BANDWIDTH With the power turned OFF, connect the RF generator and the oscilloscope to your circuit as shown in Figure 21. 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 29: 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 30 AM ALIGNMENT WITH NO TEST EQUIPMENT It is best to use an earphone for this alignment procedure. Rotate the tuning knob fully counter- clockwise and place the label on the knob with the white arrow pointing at the 540kHz marking. With an alignment tool or screwdriver, turn coils L2, T1, T2 and T3 fully counter-clockwise until they stop.

  • Page 31: Schematic Diagram

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

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