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Elenco Electronics AM/FM-108CK Assembly And Instruction Manual
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Elenco Electronics AM/FM-108CK Assembly And Instruction Manual

Am/fm radio kit
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AM/FM RADIO KIT
MODEL AM/FM-108CK SUPERHET RADIO
CONTAINS TWO SEPARATE AUDIO SYSTEMS:
IC AND TRANSISTOR
Assembly and Instruction Manual
ELENCO
®
Copyright © 2012 by ELENCO
®
All rights reserved.
753510
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/FM RADIO KIT MODEL AM/FM-108CK SUPERHET RADIO CONTAINS TWO SEPARATE AUDIO SYSTEMS: IC AND TRANSISTOR Assembly and Instruction Manual ELENCO ® Copyright © 2012 by ELENCO ® All rights reserved. 753510 No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.
  • Page 2 The AM/FM Radio project is divided into two parts, the AM Radio Section and the FM Radio Section. At this time, only identify the parts that you will need for the AM radio as listed below. DO NOT OPEN the bags listed for the FM radio.
  • Page 3 PARTS LIST FOR THE AM RADIO SECTION (continued) MISCELLANEOUS Qty. Description Part # Qty. Description Part # PC board, transistor audio amplifier 510007 Earphone 629250 PC board, main 517055 Screw M1.8 x 7.5mm (battery holder) 641100 Switch 541023 Screw M2.5 x 7.5mm (dial) 641107 Battery holder 590096...
  • Page 4 IDENTIFYING RESISTOR VALUES Use the following information as a guide in properly identifying the value of resistors. BAND 1 BAND 2 Multiplier Resistance 1st Digit 2nd Digit Tolerance Color Digit Color Digit Color Multiplier Color Tolerance BANDS Black Black Black Silver ±10% Multiplier...
  • Page 5 INTRODUCTION The Elenco ® Superhet 108C AM/FM Radio Kit is a with an understanding of what that stage has been designed “superheterodyne” receiver of the standard AM (amplitude to accomplish, and how it actually works. After each modulation) and FM (frequency modulation) broadcast assembly, you will be instructed to make certain tests and frequencies.
  • Page 6 CONSTRUCTION Introduction • Turn off iron when not in use or reduce temperature setting when using a soldering station. The most important factor in assembling your Superhet 108C AM/FM Radio Kit is good soldering techniques. Using the proper soldering iron •...
  • Page 7 SEMICONDUCTOR PARTS FAMILIARIZATION This section will familiarize you with the proper method used to test the transistors and the diode. TRANSISTOR TEST (NPN and PNP) Refer to the parts list and find a NPN transistor. Refer Refer to parts list and find a PNP transistor, refer to the Figure J (page 16) for locating the Emitter, Base Figure K (page 16) for locating the Emitter, Base and and Collector.
  • Page 8 SECTION 1A INTEGRATED CIRCUIT (IC) AUDIO AMPLIFIER This radio kit contains two separate audio Equivalent Schematic and Connection Diagrams systems. The first is an integrated circuit (IC) and the second is a five-transistor circuit. The objective 15kΩ is to show you how these two circuits function and to compare the performance of each.
  • Page 9 ASSEMBLY INSTRUCTIONS We will begin by installing resistor R43. Identify the resistor by its color and install as shown on page 4. 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. Check the box when you have completed each installation.
  • Page 10 ASSEMBLY INSTRUCTIONS Battery holder 3 Screws M1.8 x 7.5 3 Nuts M1.8 ** Solder and cut off excess leads. ** Volume/S2 (50kΩ Pot / SW) with nut & washer Plastic washer Knob (pot) Figure E Washer Foil (green) side Knob Legend Jack (blue) side...
  • Page 11 STATIC MEASUREMENTS POWER TEST For all measurements, connect your equipment GND reading if necessary. If the current is greater than 20 to circuit GND TP15. Set your VOM (Volt-Ohm- milliamps, immediately turn the power off. The Millimeter) to read 2 amps DC. Connect the meter to current should be less than 10 milliamps.
  • Page 12 If you do not have an audio generator, skip the following test and go directly to Section 1B. DYNAMIC MEASUREMENTS GAIN Connect the VOM and audio generator to the circuit lead of your VOM to the Jumper J3. Record the AC as shown in Figure 8.
  • Page 13 If an oscilloscope is not available, skip the following test and go directly to Section 1B. AC BANDWIDTH or 2.8 divisions. This frequency is called the low frequency 3dB corner. Record your answer. Connect the oscilloscope and audio generator to your circuit as shown in Figure 9.
  • Page 14 MAXIMUM POWER OUTPUT The maximum power output before distortion due to “clipping” can be calculated using the voltage Vclp Clipped obtained in the Distortion Step as follows: Vpeak (Vp) = Vclp/2 Vroot mean squared (Vrms) = Vp x 0.7 Max power out = (Vrms) /8 ohms = (Vclp x 0.35) Maximum power output should be greater than 200 milliwatts.
  • Page 15 If you do not have a power supply, Generator use a 9 volt battery instead. – Power Supply TP15 Oscilloscope TP15 Figure 11 Vp = Vclp/2 Vp = ______ Vrms = Vp x 0.7 Vrms = ______ Max power out = (Vrms) Max power out = ______ Since the battery power equals the battery voltage times the current taken from the battery;...
  • Page 16 SECTION 1B TRANSISTOR AUDIO AMPLIFIER If you have successfully completed the IC audio amplifier, you are now ready to build the five-transistor audio amplifier. The transistor audio amplifier is built on a separate PC board and will plug into the IC socket. It will be necessary to remove the IC from its socket.
  • Page 17 ASSEMBLY INSTRUCTIONS 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. Check the box when you have completed each installation. Wear safety goggles during all assembly stages in this manual.
  • Page 18 Remove IC from socket and install transistor audio amplifier PC board on the same socket. STATIC MEASUREMENTS POWER TEST Set your VOM (Volt-Ohm-Millimeter) to read 2 amps is greater than 20 milliamps, immediately turn the DC. Connect the meter to the circuit as shown in power OFF.
  • Page 19 Adjust your VOM to read 9 volts and connect it as OFF and check that all of the transistors are correctly shown in Figure 14. Make sure that the battery, or a 9 inserted in the correct locations. The E on the transistor volt power supply (if available), is properly connected indicates the emitter lead and should always be in the and turn the power ON.
  • Page 20 It is advisable to use a digital meter because of the Turn the radio ON and turn the power supply ON. small voltage changes in the following test. Connect Increase the supply voltage until the voltage at TP19 is your VOM to the circuit as shown in Figure 15. Set your equal to V .
  • Page 21 You may have to change scales on your VOM for the output voltage divided by the AC input voltage, or 1/Vin. most accurate reading. Turn the power OFF. The AC The gain should approximately equal the calculated voltage gain of your audio amplifier is equal to the AC gain.
  • Page 22 Slowly decrease the frequency of the generator until MAXIMUM POWER OUTPUT the output drops to 0.7 of its original reading, 1.4Vpp or The maximum power output before distortion due to 2.8 divisions. This frequency is called the low frequency “clipping” can be calculated using the voltage Vclp 3dB corner - the low frequency 3dB corner or (f high obtained in step 4 as follows: 3dB) - (f low 3dB).
  • Page 23 If you do not have a power supply, Generator use a 9 volt battery instead. – Power Supply TP17 Oscilloscope TP17 Figure 21 Vp = Vclp/2 Vp = ______ Vrms = Vp x 0.7 Vrms = ______ Max power out = (Vrms) Max power out = ______ Since the battery power equals the battery voltage times the current taken from the battery;...
  • Page 24 SECTION 2 AM DETECTOR AND AGC STAGE The purpose of the detector is to change the charge to approximately the same voltage as the amplitude modulated IF signal back to an audio negative peak of the IF signal. After conduction stops signal.
  • Page 25 ASSEMBLY INSTRUCTIONS C34 - 100μF Lytic R38 - 100Ω Resistor (see Figure B) (brown-black-brown-gold) T6 - AM IF Coil TP3 - Test Point Pin (Yellow Dot) (see Figure A) R35 - 27kΩ Resistor T8 - AM IF Coil (Black Dot) (red-violet-orange-gold) TP5 - Test Point Pin D4 - 1N4148 Diode...
  • Page 26 DYNAMIC MEASUREMENTS AM DETECTOR AND AGC TEST Connect your VOM and RF generator as shown in Figure 24. .001μF Generator TP15 TP15 Figure 24 Set the VOM to accurately read 2 volts DC and set generator until the voltage at TP5 just starts to drop. the output of the RF generator for 455kHz, no This point is called the AGC threshold with no IF modulation, and minimum voltage output.
  • Page 27 AM DETECTOR BANDWIDTH TEST Connect your test equipment as shown in Figure 25. increase the modulation frequency until the output Set the generator at 455kHz with 80% modulation at drops to 0.28Vpp. Record the modulation frequency a modulation frequency of 1kHz. Set the oscilloscope on the generator here: to read 0.1 volts per division.
  • Page 28 ASSEMBLY INSTRUCTIONS R39 - 39kΩ Resistor (orange-white-orange-gold) C36 - .02μF Discap (203) T7 - AM IF Coil or .022μF Discap (223) (White Dot) Q9 - 2N3904 transistor TP4 - Test Point Pin (see Figure J) (see Figure A) C37 - .02μF Discap (203) R40 - 10kΩ...
  • Page 29 DYNAMIC MEASUREMENTS AC GAIN Connect your test equipment as shown in Figure 28. Generator Oscilloscope .001μF TP15 TP15 Figure 28 Set the generator at 455kHz, no modulation and BANDWIDTH minimum voltage output. Set the oscilloscope at 1 Reconnect your test equipment as shown in Figure 28. volt per division.
  • Page 30 SECTION 4 FIRST AM IF AMPLIFIER The operation of the first IF amplifier is the same as emitter of Q8. This drop lowers the voltage across the second IF amplifier with one important difference. R37 and thus, reduces the DC current through R37. The gain of the first IF amplifier decreases after the Since all of the DC current from the emitter of Q8 AGC threshold is passed to keep the audio output...
  • Page 31 DYNAMIC MEASUREMENTS Generator Oscilloscope Short TP3 to R38 as shown below. .001μF TP15 TP15 Figure 29 AC GAIN probe to the base of Q8 and record the peak to peak level of the 455kHz signal here: Connect your test equipment as shown in Figure 29. Vb=___________Vpp.
  • Page 32 The “difference frequency” is used as the 455kHz below the oscillator frequency. The intermediate frequency in AM radios. The collector of frequency of the undesired station 455kHz above the Q7 also contains an IF transformer (T6) tuned only to oscillator is called the image frequency. If the the difference frequency.
  • Page 33 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. r Put the tab of the first holder into the right hole and twist the tab 90°. r Put the tab of the second holder into the left hole and twist the tab 90°.
  • Page 34 ASSEMBLY INSTRUCTIONS Screw M2.5 x 7.5mm Knob Fasten the knob to the shaft of the capacitor with a screw. Rotate the knob fully clockwise. Peel off the protective backing on the label. Line up the long white lines on the label with the arrows on the PC board.
  • Page 35 STATIC MEASUREMENTS Q7 BIAS Connect your VOM to the circuit as shown in Figure 30. Short TP6 to the collector of Q7 as shown. TP15 Figure 30 Connect a clip lead from TP6 to the collector of Q7. leave the power ON and check the battery voltage. If This short prevents Q7 from oscillating.
  • Page 36 AM FINAL ALIGNMENTS ALIGNMENT WITHOUT TEST There are two different AM alignment procedures. EQUIPMENT The first alignment procedure is for those who do not It is best to use an earphone for this procedure. have test equipment and the second is for those who Make sure that the switch is in the AM position.
  • Page 37 ANTENNA ALIGNMENT Tune the radio for a station around 600kHz. With the Once the antenna is properly aligned, CAREFULLY “magic wand” place the brass end near the antenna APPLY CANDLE WAX or glue to the antenna coil and coil as shown in Figure 32. If the signal heard at the the ferrite rod to prevent it from moving (see Figure 33).
  • Page 38 Set the RF generator at 455kHz, modulation of 400Hz 80% and minimum voltage out. Set the Calculate the bandwidth: __________kHz. oscilloscope to read 0.1 volts per division and turn the power ON. Increase the amplitude of the OSCILLATOR ALIGNMENT generator until the oscilloscope shows a 400Hz Set the RF generator at 540kHz, 400Hz 80% AM sinewave 5 divisions or 0.5 volts pp.
  • Page 39 Set the generator at 600kHz, 400Hz 80% brass end of the “magic wand” near the antenna coil. modulation, moderate signal strength. Set the If the signal increases, it means that the antenna coil oscilloscope to read 0.1 volt per division. Turn the needs less capacitance.
  • Page 40 DC VOLTAGES The voltage readings below should be used in troubleshooting the AM section (switch at AM position). 0.06 TP5 (AGC) TP19 Test Conditions 1. Volume set to minimum. 3. Battery voltage = 9V 2. Connect side of capacitor C29 (that goes to L4) 4.
  • Page 41 PARTS LIST FOR FM SECTION RESISTORS Qty. Symbol Value Color Code Part # R9, 23 100Ω 5% 1/4W brown-black-brown-gold 131000 220Ω 5% 1/4W red-red-brown-gold 132200 470Ω 5% 1/4W yellow-violet-brown-gold 134700 R18, 22, 24, 26, 27 1kΩ 5% 1/4W brown-black-red-gold 141000 1.8kΩ...
  • Page 42 SECTION 6 THE FM RADIO Section 6 begins the construction of the FM radio. Detector and work back to the FM Antenna. Each The stages that we will build are shown in the block stage will be tested before proceeding to the next diagram below.
  • Page 43 ASSEMBLY INSTRUCTIONS R24 - 1kΩ Resistor R23 - 100Ω Resistor (brown-black-red-gold) (brown-black-brown-gold) C21 - .01μF Discap (103) C23 - .02μF Discap (203) or .022μF Discap (223) R21 - 47kΩ Resistor (yellow-violet-orange-gold) R25 - 220Ω Resistor (red-red-brown-gold) C19 - .01μF Discap (103) C24 - 470μF Lytic T3 - FM IF Coil (see Figure S)
  • Page 44 STATIC MEASUREMENTS Battery TP15 Figure 37 FM VOLTAGE Connect your VOM as shown in Figure 37. Switch the this point should be between 7 and 9 volts. Turn the AM/FM switch to the FM position. Set your VOM to power OFF. If you do not get this reading, check R25, read 9 volts DC.
  • Page 45 If you don’t have an RF generator and oscilloscope, skip to Section 7. DYNAMIC MEASUREMENTS AC GAIN The AC gain of the ratio detector is set by the AC Reduce the generator input to maintain 150mVpp on impedance of the primary side of T4 and the current the scope.
  • Page 46 METHOD #2 Turn the power ON and set the volume control to a minimum. Increase the amplitude of the sweep ALIGNMENT OF RATIO DETECTOR USING A generator until an “S” curve is seen (refer to Figure 41). RF GENERATOR AND OSCILLOSCOPE Using an alignment tool or screwdriver, adjust the blue Connect the RF generator and oscilloscope to the coil T5 until the “S”...
  • Page 47 ASSEMBLY INSTRUCTIONS R17 - 47kΩ Resistor (yellow-violet-orange-gold) R19 - 10kΩ Resistor (brown-black-orange-gold) Q5 - 2N3904 Transistor TP10 - Test Point Pin (see Figure R) (see Figure Q) C20 - .01μF Discap (103) T2 - FM IF Coil C18 - .01μF Discap (103) (Green Dot) C17 - .01μF Discap (103) R16 - 10kΩ...
  • Page 48 Oscilloscope Generator .001μF TP15 TP15 Figure 44 DYNAMIC MEASUREMENTS AC GAIN BANDWIDTH Connect the RF generator and oscilloscope to the With the power turned OFF, connect your test circuit as shown in Figure 44. The scope probe must equipment as shown in Figure 44. Set your generator have an input capacitance of 12pF or less otherwise at 10.7MHz no modulation and minimum voltage the probe will detune T3 resulting in a false reading...
  • Page 49 SECTION 8 FIRST FM IF AMPLIFIER The operation of the first IF amplifier is the same as Capacitors C14 and C15 bypass the AC signal to the second IF amplifier except that the gain is ground. C13 and C16 are bypass capacitors from V+ different.
  • Page 50 If you don’t have an RF generator and oscilloscope, skip to Section 9. Oscilloscope Generator .001μF TP15 TP15 Figure 46 DYNAMIC MEASUREMENTS AC GAIN BANDWIDTH Connect the RF generator and oscilloscope and Connect your test equipment as shown in Figure 46. oscilloscope to the circuit as shown in Figure 46.
  • Page 51 SECTION 9 FM RF AMPLIFIER, MIXER, OSCILLATOR, AND AFC STAGE In a superheterodyne receiver, the radio waves are 10.7MHz. T1 also couples the 10.7MHz signal to the emitted and then mixed with the local oscillator to first FM IF amplifier. The RF amplifier and the produce the intermediate frequency (IF).
  • Page 52 STATIC MEASUREMENTS Q3 BIAS TP15 Figure 47 With the power turned OFF, connect your VOM to the your answer varies by more than 2 volts, turn the circuit as shown in Figure 47. Set your VOM to read power OFF and check components R7, R8, R11 and 9 volts DC and turn the power ON.
  • Page 53 Oscilloscope Generator .001μF TP15 TP15 Figure 48 BANDWIDTH TEST Turn the power OFF. The bandwidth can be calculated as follows: Connect your test equipment to the circuit as shown in Figure 48. Set your generator at 10.7MHz Bandwidth = Fh - Fl no modulation and minimum voltage output.
  • Page 54 STATIC MEASUREMENTS Q2 BIAS Connect your VOM to the circuit as shown in should be about 4 volts. Turn the power OFF. If you Figure 49. Set your VOM to read 9 volts and turn do not get this measurement, check R4, R5 and the power ON.
  • Page 55 If you don’t have an RF generator, skip to the RF Amplifier Assembly Procedure. Generator .001μF TP15 TP15 Figure 50 Connect the RF generator and VOM to the circuit as Increase the frequency of the generator until the shown in Figure 50. Set your VOM to read 9 volts DC. voltage is equal to V(D1).
  • Page 56 STATIC MEASUREMENTS Q1 BIAS Connect your VOM to the circuit as shown in Figure 51. Set your VOM to read 9 volts and turn the power ON. The voltage at the base of Q1 should be about 1.6 volts. If you do not get this reading, check R1, R2, R3 and Q1.
  • Page 57 ALIGNMENT WITH NO TEST EQUIPMENT With an alignment tool or screwdriver turn coils T1, THE COILS ANY FURTHER. Turn each coil in about T2 and T3 fully counter-clockwise. DO NOT FORCE 1¼ to 1½ turns. IF ALIGNMENT TP15 Figure 52 With an alignment tool or screwdriver turn coils T1, If the station is heard, this means that L3 needs less T2 and T3 fully counter-clockwise.
  • Page 58 is heard. Place the iron end of the “magic wand” near This concludes the alignment of the FM radio section. L3. If the station is heard, it means that L3 needs less If no stations are heard, verify that FM signals are capacitance.
  • Page 59 OSCILLATOR ALIGNMENT RF ALIGNMENT Remove the clip lead and set your generator at Set your generator at a frequency around 90MHz 88MHz modulator at 1kHz, 22.5kHz deviation and modulated at 1kHz, 22.5kHz deviation and minimum minimum voltage output. Tune the radio until a 1kHz voltage out.
  • Page 60 DC VOLTAGES The voltage readings below should be used in troubleshooting the FM section (Switch at FM position.) Test Conditions 1. Volume set to minimum. 2. Connect TP14 to TP15 with a jumper wire. 3. Battery voltage = 9V 4. All voltages are referenced to circuit common.
  • Page 61 QUIZ - FM RADIO SECTION INSTRUCTIONS: Complete the following examination, check your answers carefully. 1. The FM broadcast band is . . . 6. The ratio detector is used because ... r A) 550 - 1,600kHz. r A) it is sensitive to noise. r B) 10.7MHz.
  • Page 62 Acoustic Suspension. 2 Screws M1.8 x 7.5mm 2 Nuts M1.8 Baffle AM/FM-108CK Kit Carton 1. Start at one edge and carefully remove the baffle from the bottom the kit box. 2. Bend the four flaps upward as shown.
  • Page 63 3. Bend the top side upward as shown. 4. Bend the two sides upward. Attach the three sides using scotch tape or glue (Elmer’s, Duco Cement, or other). 5. Bend the bottom side upward and attach it to the other sides using scotch tape or glue. Bend the two mounting flaps down.
  • Page 64 SCHEMATIC DIAGRAM - AM/FM RADIO ELENCO ® 150 Carpenter Avenue Wheeling, IL 60090 (847) 541-3800 Website: www.elenco.com e-mail: elenco@elenco.com...