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 14 transistors, 5 diodes
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AM/FM RADIO KIT
MODEL AM/FM-108TK
14 TRANSISTORS, 5 DIODES
Assembly and Instruction Manual
Elenco
®
Electronics, Inc.
Copyright © 2010, 2000 by Elenco
®
Electronics, Inc. All rights reserved.
Revised 2010
REV-L
753508T
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-108TK 14 TRANSISTORS, 5 DIODES Assembly and Instruction Manual Elenco ® Electronics, Inc. Copyright © 2010, 2000 by Elenco ® Electronics, Inc. All rights reserved. Revised 2010 REV-L 753508T 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. A separate parts list will be shown for the FM radio after you have completed the AM radio.
  • Page 3 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 4: General Discussion

    INTRODUCTION The Elenco ® Superhet 108T AM/FM Radio Kit is a read before the assembly is started. This will provide the “superheterodyne” receiver of the standard AM (amplitude student with an understanding of what that stage has been modulation) and FM (frequency modulation) broadcast designed to accomplish, and how it actually works.
  • Page 5 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 108 AM/FM Transistor Radio Kit is good soldering techniques. Using the proper • Tips should be cleaned frequently to remove oxidation before it becomes soldering iron is of prime importance.
  • Page 6 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 Refer to parts list and find a PNP transistor, refer to the Figure C (page 7) for locating the Emitter, Base and Figure D (page 7) for locating the Emitter, Base and Collector.

  • Page 7: Audio Amplifier

    SECTION 1 AUDIO AMPLIFIER The purpose of the Audio Amplifier is to in-crease 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 8 ASSEMBLY INSTRUCTIONS We will begin by installing resistor R43. Identify the resistor by its color and install. 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 9 ASSEMBLY INSTRUCTIONS Note: Mount the Pot/SW, earphone jack, and speaker to the foil side of the PC Battery Holder board. 3 Screws M1.8 x 7.5 3 Nuts M1.8 Solder and cut off excess leads. Volume/S2 (50kΩ Pot / SW) Knob with Nut &...

  • Page 10: Static Measurements

    STATIC MEASUREMENTS Wear safety goggles during all tests in this manual. POWER TEST For all measurements, connect your equipment GND to meter for a more accurate reading if necessary. If the circuit GND TP15. Set your VOM (Volt-Ohm-Millimeter) current is greater than 20 milliamps, immediately turn to read 2 amps DC.
  • Page 11 Adjust your VOM to read 9 volts and connect it as OFF and check that all of the transistors are correctly shown in Figure 4. 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 12 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 TP1 is your VOM to the circuit as shown in Figure 5. Set your equal to Vo.
  • Page 13 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 14 Slowly decrease the frequency of the generator until MAXIMUM POWER OUTPUT the output drops to .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 “clipping” can be calculated using the voltage Vclp frequency 3dB corner - the low frequency 3dB corner or obtained in step 4 as follows: (f high 3dB) - (f low 3dB).
  • Page 15 If you do not have a power supply, use a 9 Generator volt battery instead. Power Supply Amps Amps COM TP15 TP15 TP15 Figure 11 Vp = Vclp/2 Vp = ______ Vrms = Vp x .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 2 AM DETECTOR AND AGC STAGE The purpose of the detector is to change the amplitude to charge to approximately the same voltage as the modulated IF signal back to an audio signal. This is negative peak of the IF signal. After conduction stops accomplished by a process called detection or in the diode (Off Condition), the capacitors will demodulation.
  • Page 17 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 (red-violet-orange-gold) (Black Dot) D4 - 1N4148 Diode TP5 - Test Point Pin (see Figure A)

  • Page 18: System Check

    DYNAMIC MEASUREMENTS AM DETECTOR AND AGC TEST Connect your VOM and RF generator as shown in Figure 14. Generator Amps COM V/Ω .001μF TP15 TP15 Figure 14 Set the VOM to accurately read 2 volts DC and set the voltage at TP5 just starts to drop. This point is called output of the RF generator for 455kHz, no modulation, the AGC threshold with no IF gain.
  • Page 19 AM DETECTOR BANDWIDTH TEST Connect your test equipment as shown in Figure 15. generator at 455kHz, but increase the modulation Set the generator at 455kHz with 80% modulation at a frequency until the output drops to .28Vpp. Record the modulation frequency of 1kHz. Set the oscilloscope to modulation frequency on the generator here: read .1 volts per division.
  • Page 20 ASSEMBLY INSTRUCTIONS R39 - 39kΩ Resistor (orange-white-orange-gold) C36 - .02μF Discap (203) TP4 - Test Point Pin (see Figure A) Q9 - 2N3904 transistor (see Figure C) T7 - AM IF Coil (White Dot) C37 - .02μF (203) or .022μF (223) Discap R40 - 10kΩ...
  • Page 21 DYNAMIC MEASUREMENTS AC GAIN Connect your test equipment as shown in Figure 18. Oscilloscope Generator .02μF Probe TP15 TP15 Figure 18 Set the generator at 455kHz, no modulation and BANDWIDTH minimum voltage output. Set the oscilloscope at 1 volt Reconnect your test equipment as shown in Figure 18. per division.
  • Page 22 SECTION 4 FIRST AM IF AMPLIFIER The operation of the first IF amplifier is the same as the lowers the voltage across R37 and thus, reduces the DC second IF amplifier with one important difference. The current through R37. Since all of the DC current from gain of the first IF amplifier decreases after the AGC the emitter of Q8 must go through R37, the DC current threshold is passed to keep the audio output constant at...

  • Page 23: Dynamic Measurements

    DYNAMIC MEASUREMENTS Short TP3 to R38 as shown below. Oscilloscope .001μF TP15 TP15 Figure 19 AC GAIN the base of Q8 and record the peak to peak level of the 455kHz signal here: Connect your test equipment as shown in Figure 19. Vb=___________Vpp.
  • Page 24 The “difference frequency” is used as the intermediate rejects this station and selects only the station 455kHz frequency in AM radios. The collector of Q7 also below the oscillator frequency. The frequency of the contains an IF transformer (T6) tuned only to the undesired station 455kHz above the oscillator is called difference frequency.
  • 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 Punch out one antenna shim from the front flap of the box.
  • Page 26 ASSEMBLY INSTRUCTIONS Figure M 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 27 STATIC MEASUREMENTS Q7 BIAS Connect your VOM to the circuit as shown in Figure 20. Short TP6 to the collector of Q7 as shown below. TP15 Figure 20 Connect a clip lead from TP6 to the collector of Q7. in your circuit differs by more than .5 volts, leave the This short prevents Q7 from oscillating.
  • Page 28 AM FINAL ALIGNMENTS ALIGNMENT WITHOUT TEST There are two different AM alignment procedures. The EQUIPMENT first alignment procedure is for those who do not have It is best to use an earphone for this procedure. Make test equipment and the second is for those who do have sure that the switch is in the AM position.

  • Page 29: Antenna Alignment

    ANTENNA ALIGNMENT Tune the radio for a station around 600kHz. With the CAREFULLY APPLY CANDLE WAX or glue to the “magic wand” place the brass end near the antenna coil antenna coil and the ferrite rod to prevent it from as shown in Figure 23.
  • Page 30 Set the RF generator at 455kHz, modulation of 400Hz ON and set the volume control to a comfortable level. 80% and minimum voltage out. Set the oscilloscope to Turn the tuning knob counter-clockwise until the white read .1 volts per division and turn the power ON. pointer is aligned at the 540kHz marking on the dial.
  • Page 31 Set the generator at 600kHz, 400Hz 80% modulation, steps. Place the brass end of the “magic wand” near the moderate signal strength. Set the oscilloscope to read antenna coil. If the signal increases, it means that the .1 volts per division. Turn the tuning knob fully counter- antenna coil needs less capacitance.
  • Page 32 QUIZ - AM SECTION INSTRUCTIONS: Complete the following examination, check your answers carefully. 1. The number of cycles produced per second by a 6. When the two metal plates on a variable source of sound is called the ... capacitor are unmeshed the ... A) amplitude.
  • Page 33 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 34 SECTION 6 THE FM RADIO Section 6 begins the construction of the FM radio. The work back to the FM Antenna. Each stage will be stages that we will build are shown in the block diagram tested before proceeding to the next stage. below.
  • Page 35 ASSEMBLY INSTRUCTIONS Notch Note: The line or notch must be R23 - 100Ω Resistor pointing to the top R24 - 1kΩ Resistor (brown-black-brown-gold) of the PC board. (brown-black-red-gold) C23 - .02μF (203) Line C21 - .01μF Discap (103) or .022μF (223) Discap C19 - .01μF Discap (103) R25 - 220Ω...

  • Page 36: Static Measurements

    STATIC MEASUREMENTS Amps COM V/Ω Battery TP15 Figure 29 FM VOLTAGE Connect your VOM as shown in Figure 29. Switch the point should be between 7 and 9 volts. Turn the power AM/FM switch to the FM position. Set your VOM to OFF.
  • Page 37 DYNAMIC MEASUREMENTS AC GAIN The AC gain of the ratio detector is set by the AC on the scope. With an alignment tool or screwdriver, impedance of the primary side of T4 and the current adjust T4 for a peak. Reduce the generator input to through Q6.
  • Page 38 METHOD #2 ON and set the volume control to a minimum. Increase the amplitude of the sweep generator until an “S” curve ALIGNMENT OF RATIO DETECTOR USING A is seen (refer to Figure 33). Using an alignment tool or RF GENERATOR AND OSCILLOSCOPE screwdriver, adjust the blue coil T5 until the “S”...
  • Page 39 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 D) (see Figure B) C20 - .01μF Discap (103) T2 - FM IF Coil C18 - .01μF Discap (103) (Green Dot) C17 - .01μF Discap (103) R16 - 10kΩ...
  • Page 40 Generator Oscilloscope .001μF TP15 Probe TP15 Figure 36 AC GAIN BANDWIDTH Connect the RF generator and oscilloscope to the With the power turned OFF, connect your test circuit as shown in Figure 36. The scope probe must equipment as shown in Figure 36. Set your generator have an input capacitance of 12pF or less otherwise the at 10.7MHz no modulation and minimum voltage probe will detune T3 resulting in a false reading of the...

  • Page 41: Static Tests

    SECTION 8 FIRST FM IF AMPLIFIER The operation of the first IF amplifier is the same as the C15 bypass the AC signal to ground. C13 and C16 are second IF amplifier except that the gain is different. The bypass capacitors from V+ to ground to prevent gain is set by the AC impedance of the primary side of feedback on the V+ line.
  • Page 42 If you don’t have an RF generator and oscilloscope, skip to Section 9. Generator Oscilloscope .001μF TP15 Probe TP15 Figure 38 Connect the RF generator and oscilloscope and BANDWIDTH oscilloscope to the circuit as shown in Figure 38. The Connect your test equipment as shown in Figure 38. scope probe must have an input capacitance of 12pF or Set your generator at 10.7MHz no modulation and less otherwise the probe will detune T2 causing an...
  • Page 43 SECTION 9 FM RF AMPLIFIER, MIXER AND OSCILLATOR In a superheterodyne receiver, the radio waves are except those near 10.7MHz. T1 also couples the emitted and then mixed with the local oscillator to 10.7MHz signal to the first FM IF amplifier. The RF produce the intermediate frequency (IF).
  • Page 44 STATIC MEASUREMENTS Q3 BIAS Amps COM V/Ω TP15 Figure 39 With the power turned OFF, connect your VOM to the are seen on the scope. With an alignment tool or a circuit as shown in Figure 39. Set your VOM to read 9 screwdriver, adjust T1 for peak.

  • Page 45: Bandwidth Test

    Generator Oscilloscope .001μF Probe TP15 TP15 Figure 40 BANDWIDTH TEST Connect your test equipment to the circuit as shown Turn the power OFF. The bandwidth can be in Figure 40. Set your generator at 10.7MHz no calculated as follows: modulation and minimum voltage output. Set the scope for 10mV per division.
  • Page 46 STATIC MEASUREMENTS Q2 BIAS Connect your VOM to the circuit as shown in Figure 41. volts. Turn the power OFF. If you do not get this Set your VOM to read 9 volts and turn the power ON. measurement, check R4, R5 and Q2. The voltage at the base of Q2 should be about 4 Amps COM V/Ω...
  • Page 47 If you don’t have an RF generator, skip to the RF Amplifier Assembly Procedure. .001μF Generator Amps COM V/Ω TP15 TP15 Figure 42 Connect the RF generator and VOM to the circuit as the frequency of the generator until the voltage is equal shown in Figure 42.
  • Page 48 STATIC MEASUREMENTS Q1 BIAS Connect your VOM to the circuit as shown in Figure 43. 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 49 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 1 1/4 to 1 1/2 turns. IF ALIGNMENT Battery Amps V/Ω...
  • Page 50 Repeat this step until the pointer is aligned to the Spacer station’s frequency. Adjusting both the oscillator coil L3 and the oscillator trimmer capacitor will effect the oscillator’s frequency, so it is advisable to repeat this Approx. Approx. procedure until the FM oscillator alignment is 1/16”...
  • Page 51 OSCILLATOR ALIGNMENT RF ALIGNMENT Remove the clip lead and set your generator at 88MHz Set your generator at a frequency around 90MHz modulator at 1kHz, 22.5kHz deviation and minimum modulated at 1kHz, 22.5kHz deviation and minimum voltage output. Tune the radio until a 1kHz signal is voltage out.

  • Page 52: Specifications

    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 53 QUIZ - FM SECTION INSTRUCTIONS: Complete the following examination, check your answers carefully. 1. The FM broadcast band is . . . 6. The ratio detector is used because ... A) 550 - 1,600kHz. A) it is sensitive to noise. B) 10.7MHz.
  • Page 54 AM/FM-108T RADIO BAFFLE NOTICE: Keep the box the kit came in. After you have completed the radio and it operates satisfactorily, you may want to install a baffle to improve the sound. 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.
  • Page 55 SCHEMATIC DIAGRAM - AM/FM-108T RADIO -54-...
  • Page 56 Elenco ® Electronics, Inc. 150 Carpenter Avenue Wheeling, IL 60090 (847) 541-3800 Website: www.elenco.com e-mail: elenco@elenco.com...

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