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1 AM-550CK_REV-A_010416.qxp 1/19/16 9:03 AM Page 1 AM RADIO KIT MODEL AM-550CK DUAL AUDIO SUPERHET INTEGRATED CIRCUIT, 7 TRANSISTORS, 2 DIODES Assembly and Instruction Manual ® ELENCO ® Copyright © 2016, 2011 by ELENCO Electronics, Inc. All rights reserved. REV-A Revised 2016 753008 No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.

2 AM-550CK_REV-A_010416.qxp 1/19/16 9:03 AM 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 DO NOT additional assistance, if needed. contact your place of purchase as they will not be able to help you. (see page 3 “Identifying Resistor Values”) RESISTORS Qty. Symbol Value Color Code Part # r 1 R19 1 1/4W 5% brown-black-gold-gold 111000 W 1/4W 5% brown-black-black-gold 121000 r 1 R21 10 W r 1/4W 5% brown-black-brown-gold 131000 3 R8, R15, R17 100 W 1/4W 5% yellow-violet-brown-gold 134700 1 R10 470 r W r 1 R18 820 W 1/4W 5% gray-red-brown-gold 138200 W r 2 R6, R16 1k 1/4W 5% brown-black-red-gold 141000 1/4W 5% brown-red-red-gold 141200 W r 1 R20 1.2k 1/4W 5% red-red-red-gold 142200 1 R12 2.2k r W 1/4W 5% orange-orange-red-gold 143300 W r 2 R3, R11 3.3k W 1/4W 5% brown-black-orange-gold 151000 r 1 R9 10k W 1 R2 12k r 1/4W 5% brown-red-orange-gold 151200 W r 1/4W 5% red-violet-orange-gold 152700 1 R5 27k 1/4W 5% orange-white-orange-gold 153900 r 1 R7 39k W 1 R14 47k W 1/4W 5% yellow-violet-orange-gold 154700 r r 1 R1 56k W 1/4W 5% green-blue-orange-gold 155600 W 1/4W 5% gray-red-orange-gold 158200 1 R13 82k r r 1/4W 5% brown-black-green-gold 171000 1 R4 1M W 1 Pot/SW1 50k / SW Pot/SW with nut and washer 192522 r W (see page 3 “Identifying Capacitor Values”) CAPACITORS Qty. Symbol Value Description Part # 1 C1 Variable Tuning 211677 r m r 1 C15 0.001 F Discap (102) 231036 2 C3, C10 0.01 m F Discap (103) 241031 r 5 C2, C5, C7, C8, C9 0.02 m r m F Discap (203) or (223) 242010 F or 0.022 r m F Discap (473) 244780 1 C20 0.047 1 C19 0.1 m r F Discap (104) 251010 m r F Electrolytic (Lytic) 271045 5 C4,C11,C16,C17,C18 10 F Electrolytic (Lytic) 274744 r 1 C12 47 m F Electrolytic (Lytic) 281044 1 C6 100 r m F Electrolytic (Lytic) 284744 m r 2 C13, C14 470 SEMICONDUCTORS Qty. Symbol Description Part # r 2 D1, D2 1N4148 Diode 314148 r 4 Q1, Q2, Q3, Q4 2N3904 Transistor NPN 323904 r 1 Q5 2N3906 Transistor PNP 323906 1 Q6 MPS8050 or 6560 Transistor NPN 328050 r r 1 Q7 MPS8550 or 6562 Transistor PNP 328550 r 1 U1 LM386 Integrated circuit 330386 COILS Qty. Symbol Value Description Part # r 1 L2 Oscillator (red dot) 430057 r 1 T1 IF (yellow dot) 430260 r 1 T2 IF (white dot) 430262 1 T3 Detector (black dot) 430264 r r 1 L1 AM Antenna with holders 484004 MISCELLANEOUS Qty. Description Part # Qty. Description Part # r 1 Screw M2.5 x 8mm (gang) 641107 1 PC board 517039 r r 1 Switch 541023 2 Screw 2.5 x 4mm (gang) 641310 r r 4 Nut M1.8 644210 r 1 Battery holder 590096 r 1 Speaker 590102 1 Socket 8-pin 664008 r 10 Test point pin 665008 r 1 Knob (dial) 622040 r 1 Knob (pot) 622050 r r 1 Label, dial knob 720422 1 Earphone jack with nut 622130 r r 1 Speaker pad 780128 1 Radio stand 626100 r r 1 Wire 4” 814920 1 Solder lead-free 9LF99 r 1 Earphone 629250 r r 4 Screw M1.8 x 7mm (battery holder) 641100 **** SAVE THE BOX THAT THIS KIT CAME IN. IT WILL BE USED ON PAGES 29 AND 34. **** -1-

3 AM-550CK_REV-A_010416.qxp 1/19/16 9:03 AM Page 3 PARTS IDENTIFICATION SEMICONDUCTORS RESISTORS CAPACITORS Diode Resistor LM386 IC 50k W Potentiometer/ Electrolytic Tuning Discap Switch Radial with Nut and Washer 8-pin Socket Transistor Color dot COILS Plastic holders Coil Ferrite core Antenna Assembly Coil MISCELLANEOUS Earphone Slide Switch Knob (dial) Battery Knob (pot) Label Speaker Pad Holder Speaker Test Point Pin Screw Nut M2.5 x 4mm M1.8 Screw Screw Earphone Jack M2.5 x 8mm M1.8 x 7mm Radio Stand with Nut -2-

4 AM-550CK_REV-A_010416.qxp 1/19/16 9:03 AM Page 4 IDENTIFYING RESISTOR VALUES Use the following information as a guide in properly identifying the value of resistors. BAND 1 Resistance Multiplier BAND 2 1st Digit Tolerance 2nd Digit Color Digit Color Color Multiplier Tolerance Digit Color BANDS Black 0 0 Black Black 1 ±10% Silver 2 Multiplier Tolerance 1 1 Brown 1 Gold Brown 10 Brown ±5% 2 Red Red Brown 2 100 Red ±1% 3 Orange 1,000 Orange Orange ±2% Red 3 Yellow 4 Orange Yellow 4 Yellow ±3% 10,000 5 Green ±0.5% Green Green Green 100,000 5 Blue 6 Blue 1,000,000 6 Blue ±0.25% Blue 7 Violet ±0.1% Violet 0.01 Silver 7 Violet 8 Gray 8 0.1 Gold Gray 9 White 9 White IDENTIFYING CAPACITOR VALUES Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or m F (microfarads). Most capacitors will have their actual value printed on them. Some capacitors may have their value printed in the following manner. The maximum operating voltage may also be printed on the capacitor. Electrolytic capacitors have a positive 2 8 5 4 3 9 1 0 For the No. and a negative electrode. The Multiplier negative lead is indicated on the 1 Multiply By 10k 1k .01 100k 0.1 100 10 packaging by a stripe with minus signs and possibly arrowheads. Also, the CERAMIC DISC MYLAR negative lead of a radial electrolytic is Tolerance * shorter than the positive one. Second digit Multiplier Multiplier 101K Second digit Tolerance * 100V First digit Warning: 50V 2A222J First digit If the capacitor is connected with incorrect polarity, it Maximum working voltage (may or may not appear may heat up and on the cap) Polarity either leak, or The value is 22 x 100 = marking 2,200pF or .0022 m F, + 5%, 100V cause the capacitor The value is 10 x 10 = 100pF, + 10%, 50V to explode. (–) 20% The letter M indicates a tolerance of + * (+) 10% The letter K indicates a tolerance of + The letter “R” may be used at times Note: (–) (+) The letter J indicates a tolerance of + 5% to signify a decimal point; as in 3R3 = 3.3 Radial Axial METRIC UNITS AND CONVERSIONS Abbreviation Means Multiply Unit By Or 1. 1,000 pico units = 1 nano unit -12 p Pico .000000000001 10 2. 1,000 nano units = 1 micro unit -9 n nano .000000001 10 3. 1,000 micro units = 1 milli unit -6 micro .000001 10 m -3 m milli .001 10 4. 1,000 milli units = 1 unit 0 – unit 1 10 5. 1,000 units = 1 kilo unit 3 k kilo 1,000 10 6 6. 1,000 kilo units = 1 mega unit M mega 1,000,000 10 -3-

5 AM-550CK_REV-A_010416.qxp 1/19/16 9:03 AM Page 5 INTRODUCTION ® Dual Audio Superhet 550C AM Radio is The Elenco This will provide the student with an understanding of a “superheterodyne” receiver of the standard AM what that stage has been designed to accomplish, (amplitude modulated) broadcast frequencies. The and how it actually works. After each assembly, you unique design of the Superhet 550C allows you to will be instructed to make certain tests and place the parts over its corresponding symbol in the measurements to prove that each section is schematic drawing on the surface of the printed circuit functioning properly. If a test fails to produce the board during assembly. This technique maximizes the proper results, a troubleshooting guide is provided to learning process while keeping the chances of an help you correct the problem. If test equipment is assembly error at a minimum. It is very important, available, further measurements and calculations are however, that good soldering practices are used to demonstrated to allow each student to verify that each prevent bad connections. The Soldering Guide should stage meets the engineering specifications. After all be reviewed before any assembly is attempted. of the stages have been built and tested, a final alignment procedure is provided to peak the The actual assembly is broken down into five performance of the receiver and maximize the Dual sections. The theory of operation for each section, or Audio Superhet 550C’s reception capabilities. stage, should be read before the assembly is started. GENERAL DISCUSSION bandwidth of this stage should be approximately The Dual Audio Superhet 550C can best be 6kHz. Section 4 is the first IF amplifier which has a understood by analysis of the block diagram shown variable gain that depends on the AGC voltage in Figure 1. received from the AGC stage. The first IF amplifier is The purpose of section 1, the Audio Amplifier Stage, also tuned to 455kHz and has a 3dB bandwidth of is to increase the power of the audio signal received approximately 6kHz. Section 5 includes the mixer, from the detector to a power level capable of driving oscillator and antenna stages. When the radio wave the speaker. The audio amplifier is switchable passes through the antenna, it induces a small between transistor or IC function. voltage across the antenna coil. This voltage is Section 2 includes the detector circuit and the AGC coupled to the mixer, or converter, stage to be (automatic gain control) circuit. The detector converts changed to a frequency of 455kHz. This change is the amplitude modulated IF (intermediate frequency) accomplished by mixing (heterodyning) the radio signal to a low level audio signal. The AGC stage frequency signal with the oscillator signal. Each of feeds back a DC voltage to the first IF amplifier in these blocks will be explained in detail in the Theory order to maintain a near constant level of audio at the of Operation given before the assembly instructions detector. Section 3 is the second IF amplifier. The for that stage. second IF amplifier is tuned to 455kHz (kilohertz) and has a fixed gain at this frequency of 100. The 3dB Antenna Section 3 Section 1 Section 2 Section 4 Section 5 Speaker TRANSISTOR FIRST SECOND AUDIO DETECTOR MIXER IF AMPLIFIER IF AMPLIFIER AMPLIFIER LOCAL IC AUDIO AGC OSCILLATOR AMPLIFIER Figure 1 -4-

6 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 6 CONSTRUCTION ● Turn off iron when not in use or reduce temperature setting when Introduction ® using a soldering station. The most important factor in assembling your Elenco Dual Audio Superhet 550C AM Radio Kit is good soldering techniques. Using the ● Tips should be cleaned frequently to remove oxidation before it becomes proper soldering iron is of prime importance. A small pencil type soldering ® #SH-1025) or Tip impossible to remove. Use Dry Tip Cleaner (Elenco The tip of the iron must be kept iron of 25 watts is recommended. ® Cleaner (Elenco #TTC1). If you use a sponge to clean your tip, then use clean at all times and well-tinned. distilled water (tap water has impurities that accelerate corrosion). Solder Safety Procedures For many years leaded solder was the most common type of solder used Always wear safety glasses or safety goggles to protect ● by the electronics industry, but it is now being replaced by lead-free your eyes when working with tools or soldering iron, solder for health reasons. This kit contains lead-free solder, which and during all phases of testing. contains 99.3% tin, 0.7% copper, and has a rosin-flux core. when soldering. Be sure there is adequate ventilation ● Lead-free solder is different from lead solder: It has a higher melting point than lead solder, so you need higher temperature for the solder to flow Locate soldering iron in an area where you do not have to go around ● O F; higher properly. Recommended tip temperature is approximately 700 it or reach over it. Keep it in a safe area away from the reach of temperatures improve solder flow but accelerate tip decay. An increase children. in soldering time may be required to achieve good results. Soldering iron ● Do not hold solder in your mouth. Solder is a toxic substance. tips wear out faster since lead-free solders are more corrosive and the Wash hands thoroughly after handling solder. higher soldering temperatures accelerate corrosion, so proper tip care is important. The solder joint finish will look slightly duller with lead-free Assemble Components solders. In all of the following assembly steps, the components must be installed Use these procedures to increase the life of your soldering iron tip when on the top side of the PC board unless otherwise indicated. The top using lead-free solder: legend shows where each component goes. The leads pass through the corresponding holes in the board and are soldered on the foil side. ● Keep the iron tinned at all times. Use only rosin core solder. Use the correct tip size for best heat transfer. The conical tip is the ● DO NOT USE ACID CORE SOLDER! most commonly used. What Good Soldering Looks Like Types of Poor Soldering Connections A good solder connection should be bright, shiny, smooth, and uniformly flowed over all surfaces. Soldering Iron Rosin Component Lead Insufficient heat 1.Solder all components from the 1. - the solder will Foil copper foil side only. Push the not flow onto the lead as shown. soldering iron tip against both the lead and the circuit board foil. Soldering iron positioned Circuit Board incorrectly. Solder Soldering Iron - let the solder Insufficient solder 2. 2.Apply a small amount of solder to flow over the connection until it is Solder the iron tip. This allows the heat to covered. leave the iron and onto the foil. Use just enough solder to cover Immediately apply solder to the Foil the connection. Gap opposite side of the connection, away from the iron. Allow the Component Lead heated component and the circuit foil to melt the solder. Solder Excessive solder 3. - could make connections that you did not intend to between adjacent foil Soldering Iron Solder areas or terminals. 3.Allow the solder to flow around the connection. Then, remove the Foil solder and the iron and let the connection cool. The solder should have flowed smoothly and Soldering Iron 4. Solder bridges - occur when not lump around the wire lead. solder runs between circuit paths and creates a short circuit. This is usually caused by using too much solder. Here is what a good solder 4. To correct this, simply drag your connection looks like. soldering iron across the solder bridge as shown. Drag Foil -5-

7 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM 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 parts list and find a PNP transistor, refer to Refer to the parts list and find a NPN transistor. Refer Figure B (page 8) for locating the Emitter, Base and the Figure A (page 8) for locating the Emitter, Base and Collector. Using an Ohmmeter, connect the transistor as Collector. Using an Ohmmeter, connect the transistor as shown in Test C. Your meter should be reading a low shown in Test A. Your meter should be reading a low resistance. Switch the lead from the Emitter to the resistance. Switch the lead from the Emitter to the Collector. Your meter should again be reading a low Collector. Your meter should again be reading a low resistance. resistance. Using an Ohmmeter, connect the transistor as shown in Using an Ohmmeter, connect the transistor as shown in Test D. Your meter should be reading a high resistance. Test B. Your meter should be reading a high resistance. Switch the lead from the Emitter to the Collector. Your Switch the lead from the Emitter to the Collector. Your meter should again be reading a high resistance. Typical meter should again be reading a high resistance. W results read approximately 1M to infinity. Low Resistance High Resistance Low Resistance High Resistance W W W W COM PNP COM W NPN W NPN PNP W COM W COM EBC EBC EBC EBC TEST A TEST C TEST B TEST D DIODE TEST Refer to the parts list and find a diode. Refer to Figure E connect the diode as shown in Test F. Your meter should (page 8) for locating the Cathode and Anode. The end be reading a high resistance. Typical results read W with the band is the cathode. Using an Ohmmeter, approximately 1M to infinity for silicon diodes connect the diode as shown in Test E. Your meter should (1N4148). be reading a low resistance. Using an Ohmmeter, High Resistance Low Resistance W W W COM COM W Diode Diode TEST E TEST F -6-

8 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 8 SECTION 1A TRANSISTOR AUDIO AMPLIFIER Transistor Q4 is a Class A amplifier that drives the base Theory of Operation - The purpose of the Audio Amplifier is to increase the audio power to a level of transistor Q5 directly. Q5 is a current amplifier that multiplies the collector current of Q4 by the beta (current sufficient to drive an 8 ohm speaker. To do this, DC gain, B) of Q5. The current from Q5 drives the output (direct current) from the battery is converted by the transistors Q6 and Q7 through the bias string R17, D2 amplifier to an AC (alternating current) in the speaker. and R18. Bias stability is achieved by using 100% DC The ratio of the power delivered to the speaker and the feedback from the output stage to the emitter of Q4 power taken from the battery is the efficiency of the through resistor R16. This gives the Audio Amplifier a DC amplifier. In a Class A amplifier (transistor on over entire gain of one. The AC gain is set by resistors R16, R15 cycle) the maximum theoretical efficiency is 0.5 or 50%, but in a Class B amplifier (transistor on for 1/2 cycle) the and capacitor C12. In this circuit, the value of R16 is maximum theoretical efficiency is 0.785 or 78.5%. Since 1000 ohms and R15 is 100 ohms. Their ratio is 10 to 1, therefore the AC gain of the amplifier is 10 times. transistor characteristics are not ideal, in a pure Class B amplifier, the transistors will introduce crossover Resistors R13 and R14 set the DC voltage at the base of Q4 to approximately 5.2V. The emitter of Q4 is set at distortion. This is due to the non-linear transfer curve 4.5V, which is the same voltage at this output to the near zero current or cutoff. This type distortion is shown speaker. Note that this voltage is 1/2 the battery voltage. in Figure 2. Capacitor C11 AC couples the audio signal from the In order to eliminate crossover distortion and maximize volume control to the input of the Audio Amplifier. efficiency, the transistors (Q6 and Q7) of the audio Capacitor C13 blocks the DC to the speaker, while amplifier circuit are biased on for slightly more than 1/2 allowing the AC to pass. of the cycle, Class AB. In other words, the transistors are working as Class A amplifiers for very small levels of power to the speaker, but they slide toward Class B operation at larger power levels. Figure 2 -7-

9 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM 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. Check the box when you have completed each installation. Warning: If the capacitor is connected with incorrect polarity, Electrolytics have a polarity NPN Transistor marking indicating the (–) lead. or if it is subjected to voltage exceeding its working voltage, Mount so E lead is in The PC board is marked to it may heat up and either leak or cause the capacitor to the arrow hole and flat side is in the same show the lead position. explode. direction as shown on the top legend. Leave Capacitor C14 Polarity mark 1/4” between the part Flat side For safety, solder and PC board. capacitor C14 on the 1/4” Figure A copper side as shown. Bend the leads 90° and insert into holes. Check PNP Transistor + that the polarity is correct, Mount so E lead is in Flat side then solder in place. Trim the arrow hole and flat side is in the same the excess leads on (–) (+) direction as shown on 1/4” legend side. – the top legend. Leave Figure Da Figure Db 1/4” between the part and PC board. Test Point Pin Diode Figure B Be sure that the band is in Legend side the correct direction. of PC board Band Jumper Wire Q5 - 2N3906 Transistor PNP Use an excess lead to form a jumper (see Figure B) wire. Bend the wire to the correct Cathode Anode length and mount it to the PC board. TP7 - Test Point Pin Figure F 1/8” (see Figure F) Figure E Q6 - MPS8050 (6560) Figure C Transistor NPN (see Figure A) W R14 - 47k Resistor W Resistor R19 - 1 (yellow-violet-orange-gold) (brown-black-gold-gold) Q4 - 2N3904 Transistor NPN R17 - 100 Resistor W (see Figure A) (brown-black-brown-gold) TP6 - Test Point Pin TP8 - Test Point Pin (see Figure F) (see Figure F) J1 - Jumper Wire m C13 - 470 F Lytic (see Figure C) (see Figure Da) C11 - 10 m F Lytic SW2 - Slide Switch (see Figure Da) Q7 - MPS8550 (6562) Resistor R13 - 82k W Transistor PNP (see Figure B) (gray-red-orange-gold) Resistor W R18 - 820 m C14 - 470 F Lytic (gray-red-brown-gold) (see Figure Db) D2 - 1N4148 Diode Pot / SW1 with (see Figure E) Nut and Washer Knob (pot) Resistor R16 - 1k W (brown-black-red-gold) Top Side TP10 - Test Point Pin Solder 5 lugs (see Figure F) to PC board W R15 - 100 Resistor C12 - 47 F Lytic m (brown-black-brown-gold) (see Figure Da) -8-

10 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 10 ASSEMBLY INSTRUCTIONS Figure G Your kit may contain a different type of J1 - Earphone Jack earphone jack. Before installing the jack, with Nut determine which one you have. (see Figure G) GND pad Foil side Speaker 1 Speaker Pad Nut Jack 4” Wire 2 (see Figures H & I) 3 Battery Holder 1 - GND 3 Screws M1.8 x 7mm 2 - Tip 3 Nuts M1.8 3 - N.C. Tip Solder and cut off excess leads. Mount the jack with the nut from the foil side of the PC board (terminal #1 on the GND pad of the PC board). Be sure to line up the tab with the pad on the copper side of the PC board. Solder terminal #1 to the pad of the PC board. Step 2 Step 3 Step 1 Figure H Pad Step 1: If the speaker pad has center and outside pieces, then remove them. Peel the backing off of one side of the Backing speaker pad and stick the pad onto the speaker. PC Board (solder side) Backing Speaker Step 2: Remove the other backing from the speaker pad. Stick the speaker onto the Step 3: solder side of the PC board. Figure I Cut two 1” wires and one 1½” wire and strip ¼” of insulation off of both ends. Solder the wires in the locations shown. 1½” Wire 1” Wires -9-

11 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 11 You have completed wiring the Transistor Audio Amplifier. We shall proceed in testing this circuit. You will need a Volt- Ohm-Milliammeter, preferably a digital type. STATIC MEASUREMENTS - TRANSISTOR AUDIO AMPLIFIER (SW2 on the top [TR] position) RESISTANCE TEST Adjust the Volt-Ohm-Milliammeter (VOM) to the highest , check the W leads. If you get a reading lower than 20k resistance scale available. Connect the VOM to the circuit for shorts or parts inserted incorrectly. Check C14 circuit as shown in Figure 3. Do not connect the battery. to see if it’s leaky or inserted backwards. If you get a The VOM should indicate a low resistance first and then reading higher than 150k W , check for open copper or as C14 charges, resistance should rise to approximately bad solder connections on resistors R13 and R14. . If you get a lower reading, reverse multimeter W 100k GND TP10 Figure 3 POWER UP TEST Set your VOM to read the highest possible DC current. Adjust your meter for a more accurate reading if necessary. Connect the meter to the circuit as shown in Figure 4. If the current is greater than 25 milliamps, immediately turn Make sure that the On/Off switch (SW1) is in the OFF the power off. The current should be between 5 and 15 milliamps. If you circuit fails this test, check that all parts position. While watching your VOM, flip switch SW1 to the ON have been installed correctly and check for shorts or poor solder connections. Turn OFF SW1. position. The VOM should indicate a very low current. + – Figure 4 -10-

12 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 12 OUTPUT BIAS TEST Adjust your VOM to read 9 volts DC and connect it to test circuit fails this test, turn the power OFF and check that point 8 (TP8) as shown in Figure 5. all of the transistors are correctly inserted in the correct Make sure that the battery, or a 9 volt power supply (if locations. The E on the transistor indicates the emitter available), is properly connected and turn the power ON. lead and should always be in the hole with the arrow. The voltage at TP8 should be between 4.5 to 5.5 volts. Check that resistors R13 and R14 are the correct values and not interchanged. If you get this reading, go on to the next test. If your GND TP10 Figure 5 TRANSISTOR BIAS TEST approximately 0.7V from the base to the emitter. If your Move the positive lead of your VOM to test point 7 (TP7). circuit fails this test, turn off the power and check that Make sure that the power is ON. The voltage should be between 0.5 and 0.8V higher than the voltage at TP8. Q6 is properly inserted into the circuit board. All silicon transistors biased for conduction will have INPUT BIAS Move the positive lead of the VOM to test point 6 (TP6). test, leave the VOM connected and go to test 1 in the Make sure that the power is ON. The voltage at TP6 Dynamic Measurements Section. If your circuit fails this should be very close to the voltage at TP7. This is true test, turn the power OFF and check transistors Q4, Q7 because very little DC current flows through resistor R16 and resistor R16. All static tests must pass before making the voltage at the emitter of Q4 very close to the proceeding to the Dynamic Tests or the next section. voltage at the emitter of Q6. If your circuit passes this -11-

13 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 13 DYNAMIC MEASUREMENTS DC GAIN Adjust your VOM to read 9 volts DC. Connect the Once again, parallel resistor R13 with resistor R4 as positive lead of the VOM to TP6 and the negative lead shown in Figure 6. The voltage at TP8 should also drop to TP10. Turn the power ON and record the voltage at to a lower voltage. Record the new reading at TP8 here: TP6 here: V4=__________ volts. V1=________ volts. Remove R4 from the circuit but leave your VOM Place resistor R4 across resistor R13 as shown in connected to TP8 for the next test. Turn the power OFF. Figure 6. Since the DC GAIN equals the DC change at the output The voltage at TP6 should drop to a lower value. Record divided by the DC change at the input, the DC gain of that lower voltage here: this amplifier is (V1-V2)/(V3-V4). Your calculated answer should be very close to 1. V2=__________ volts. Remove R4 from the circuit and move the positive lead of the VOM to TP8. Record the voltage at TP8 here: V3=__________ volts. 1M W GND TP10 Figure 6 If you do not have a generator, skip the following test and go directly to Section 1B. -12-

14 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 14 AC GAIN Connect the VOM and generator to TP6 as shown in the positive lead of your VOM to TP6. Record the AC Figure 7. voltage input to the amplifier here: Turn the power ON. Normally the AC gain is measured at a frequency of 1 kilohertz (kHz). Your VOM, however, Vin=___________ volts. may not be able to accurately read AC voltages at this frequency. It is recommended, therefore, that this test be You may have to change scales on your VOM for the performed at 400Hz. Set the generator at 400Hz and most accurate reading. Turn the power OFF. The AC minimum voltage output. Set your VOM to read an AC voltage gain of your Audio Amplifier is equal to the AC output voltage divided by the AC input voltage, or 1/Vin. voltage of 1 volt at the output of your Audio Amplifier. Slowly increase the output of the generator until the VOM Your calculated AC Gain should be approximately 10. reads 1 volt AC. Leave the audio at this setting and move Generator F m 10 Output Adjust GND TP10 GND TP10 Figure 7 If an oscilloscope is not available, skip the following test and go directly to Section 2. -13-

15 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 15 AC BANDWIDTH waveform on the oscilloscope drops to 0.7 of its original Connect the oscilloscope (set to AC input measurement) and generator to your circuit as shown in Figure 8. reading, 1.4 Vpp or 2.8 divisions. Use the oscilloscope probe to check TP6 to make sure the input voltage did Set the generator for a frequency of 1kHz and minimum not change. The frequency of the generator when the voltage output. Set the oscilloscope to read 0.5 volts per output drops to 0.7 of its original value is called the high division. Turn the power ON and slowly increase the generator output until the oscilloscope displays 2 volts frequency 3 decibel (dB) corner. peak to peak (Vpp) at TP8. Move the oscilloscope probe to TP6 and record the input voltage here: Repeat this procedure by lowering the frequency from the generator to obtain the low frequency 3dB corner. Vin=___________ Vpp Leave the oscilloscope connected to TP8 and turn the power OFF. By subtracting the frequency of the low (at this point you may want to verify the AC Gain). corner from the frequency of the high corner, you calculate the bandwidth of the Audio Amplifier. Your Move the oscilloscope probe back to TP8 and slowly bandwidth should be greater than 100kHz. increase the frequency from the generator until the Oscilloscope Generator m F 10 Output Adjust GND TP10 Probe GND TP10 Figure 8 -14-

16 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 16 DISTORTION peaks of the sinewave at TP8 are clipped as shown in Connect the generator and oscilloscope as shown in Figure 8. Set the generator at a frequency of 1kHz, turn Figure 9A. the power ON and adjust the generator output until the Clipped Crossover distortion A B Figure 9 The waveform on your oscilloscope should resemble Measure the maximum voltage peak to peak when clipping Figure 9B. The “flat spots” near the center of each first occurs and record that value here: sinewave demonstrate what is called crossover Vclp = _______ Vpp. distortion. This distortion should disappear when you remove the shorting lead. Turn the power OFF Using a wire short out resistor R17 and diode D2 as shown in Figure 10. MAXIMUM POWER OUTPUT The maximum power output before distortion due to “clipping” can be calculated using the voltage Vclp obtained in step 4 as follows: Wire lead or clip lead Vpeak (Vp) = Vclp/2 Vroot mean squared (Vrms) = Vp x .7 2 2 Max power out = (Vrms) /8 ohms = (Vclp x .35) /8 Maximum power output should be greater than 200 milliwatts. Figure 10 EFFICIENCY By measuring the DC power taken from the battery at voltage from changing during this measurement. the maximum power output level, the efficiency to the Efficiency can then be calculated as follows: Audio Amplifier can be calculated. Power from the battery is equal to the current taken from the battery Eff = times the voltage of the battery during maximum power Max audio power output. It is best to use a power supply to prevent battery Battery power / -15-

17 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 17 SECTION 1B INTEGRATED CIRCUIT (IC) AUDIO AMPLIFIER For the IC Audio Amplifier, we use the integrated circuit (IC) LM-386. In Figure 11, you can see equivalent schematic and connection diagrams. Figure 12a Dual In-Line and Small Outline Packages Top View Figure 11 Figure 12b To make the LM-386 a more versatile amplifier, two pins (1 and 8) are provided for gain control. With pins W 1 and 8 open, the 1.35k resistor sets the gain at 20 (see Figure 12a). The gain will go up to 200 (see Figure 12b) if a capacitor is placed between pins 1 and 8. The gain can be set to any value from 20 to 200 if a resistor is placed in series with the capacitor. The amplifier in our kit with a gain of 50 is shown in Figure 13. Capacitor C11 couples the audio signal from the volume control to the input of the audio amplifier. Capacitor C13 blocks the DC to the speaker, while allowing the AC to pass. Figure 13 -16-

18 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 18 ASSEMBLY INSTRUCTIONS F (473) Discap m C20 - .047 Integrated Circuit Insert the IC socket into the PC F Lytic Capacitor m C18 - 10 board with the notch in the direction C16 - 10 F Lytic Capacitor m shown on the top legend. Solder (see Figure Da) the IC socket into place. Insert the IC into the socket with the notch in 5% 1/4W Resistor W R20 - 1.2k the same direction as the notch on (brown-red-red-gold) the socket. TP9 - Test Point Pin IC (see Figure F) m F Lytic Capacitor C17 - 10 IC socket Notch (see Figure Da) U1 - IC Socket 8-Pin U1 - Integrated Circuit LM-386 PC board (see Figure J) C19 - 0.1 m F Discap (104) 5% 1/4W Resistor R21 - 10 W Notch marking (brown-black-black-gold) Figure J You have completed wiring the IC 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 - IC AUDIO AMPLIFIER (SW2 on the down [IC] position) RESISTANCE TEST Adjust the Volt-Ohm-Milliammeter (VOM) to the highest 4M W . If you get a lower reading, reverse multimeter resistance scale available. Connect the VOM to pin 6 of W , check the leads. If you get a reading lower than 100k the IC as shown in Figure 14. Do not connect the battery. circuit for shorts or parts inserted incorrectly. If you get The VOM should indicate a low resistance first and then a reading higher than 10M W , check for open copper or as C14 charges, resistance should rise to approximately bad solder connections on all components. GND TP10 Figure 14 -17-

19 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 19 POWER UP TEST Set your VOM to read the highest possible DC current. necessary. If the current is greater than 25 milliamps, Connect the meter to the circuit as shown in Figure 15. immediately turn the power off. The current should be Make sure that the On/Off switch (SW1) is in the OFF between 3 and 15 milliamps. If you circuit fails this test, check that all parts have been installed correctly and position. While watching your VOM, flip switch SW1 to the ON check for shorts or poor solder connections. Turn OFF SW1. position. The VOM should indicate a very low current. Adjust your meter for a more accurate reading if + – Figure 15 INPUT BIAS OUTPUT BIAS TEST Adjust your VOM to read 9 volts DC and connect it to Move the positive lead of the VOM to test point 9 (TP9). test point 8 (TP8) as shown in Figure 16. Make sure that the power is ON. The voltage at TP9 Make sure that the battery, or a 9 volt power supply (if should be close to the voltage at test point 10 (TP10). If available), is properly connected and turn the power ON. your circuit passes this test, leave the VOM connected The voltage at TP8 should be between 4 to 5 volts. If and go to test 1 in the Dynamic Measurements Section. you get this reading, go on to the next test. If your circuit If your circuit fails this test, turn the power OFF and fails this test, turn the power OFF and check that the check the IC. All static tests must pass before integrated circuit is correctly inserted in the correct proceeding to the Dynamic Tests or the next section. locations. GND TP10 Figure 16 If you do not have an audio generator, skip the following test and go directly to Section 2. -18-

20 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 20 DYNAMIC MEASUREMENTS AC GAIN Connect the VOM and audio generator as shown in of the audio generator until the VOM reads 1 volt AC. Figure 17. Turn the power ON. Normally the AC gain is Leave the audio at this setting and move the positive measured at a frequency of 1 kilohertz (kHz). Your VOM, lead of your VOM to TP9. Record the AC voltage input to the amplifier here: Vin=___________ volts. You may however, may not be able to accurately read AC have to change scales on your VOM for the most voltages at this frequency. It is recommended, therefore, that this test be performed at 400Hz. Set the audio accurate reading. Turn the power OFF. The AC voltage gain of your Audio Amplifier is equal to the AC output generator at 400Hz and minimum voltage output. Set your VOM to read an AC voltage of 1 volt at the output voltage divided by the AC input voltage, or 1/Vin. Your of your Audio Amplifier (TP8). Slowly increase the output calculated AC Gain should be approximately 30 - 50. F m 10 Generator GND TP10 Output Adjust GND Figure 17 TP10 If an oscilloscope is not available, skip the following test and go directly to Section 2. AC BANDWIDTH Connect the oscilloscope and audio generator to your divisions Use the oscilloscope probe to check TP9 to circuit as shown in Figure 18. make sure the input voltage did not change. The Set the audio generator for a frequency of 1kHz and frequency of the generator when the output drops to 0.7 minimum voltage output. Set the oscilloscope to read of its original value is called the high frequency 3 decibel 0.5 volts per division. Turn the power ON and slowly (dB) corner. increase the generator output until the oscilloscope Repeat this procedure by lowering the frequency from displays 2 volts peak to peak (Vpp) at TP8. Move the the generator to obtain the low frequency 3dB corner. oscilloscope probe to TP9 and record the input voltage Leave the oscilloscope connected to TP8 and turn the here: Vin=___________ Vpp, (at this point you may power OFF. By subtracting the frequency of the low want to verify the AC Gain). Move the oscilloscope probe corner from the frequency of the high corner, you back to TP8 and slowly increase the frequency from the calculate the bandwidth of the Audio Amplifier. Your audio generator until the waveform on the oscilloscope bandwidth should be greater than 100kHz. drops to 0.7 of its original reading, 1.4 Vpp or 2.8 -19-

21 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 21 Oscilloscope F 10 m Generator Probe GND TP10 Output Adjust GND TP10 Figure 18 DISTORTION peaks of the sinewave at TP8 are clipped as shown in Connect the generator and oscilloscope as shown in Figure 18. Set the generator at a frequency of 1kHz, turn Figure 9A. the power ON and adjust the generator output until the Measure the maximum voltage peak to peak when clipping first occurs and record that value here: Vclp = _______ Vpp. MAXIMUM POWER OUTPUT The maximum power output before distortion due to “clipping” can be calculated using the voltage Vclp obtained in step 3 as follows: Vpeak (Vp) = Vclp/2 Vroot mean squared (Vrms) = Vp x .7 2 2 Max power out = (Vrms) /8 ohms = (Vclp x .35) /8 Maximum power output should be greater than 200 milliwatts. EFFICIENCY By measuring the DC power taken from the battery at output. It is best to use a power supply to prevent battery the maximum power output level, the efficiency to the voltage from changing during this measurement. Audio Amplifier can be calculated. Power from the Efficiency can then be calculated as follows: battery is equal to the current taken from the battery times the voltage of the battery during maximum power Max power output Eff = Battery power / -20-

22 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 22 SECTION 2 AM DETECTOR AND AGC STAGES THEORY OF OPERATION The purpose of the detector is to change the amplitude The purpose of the automatic gain control (AGC) circuit modulated IF signal back to an audio signal. This is is to maintain a constant audio level at the detector, accomplished by a process called detection or regardless of the strength of the incoming signal. demodulation. First, the amplitude modulated IF signal Without AGC, the volume control would have to be is applied to a diode in such a way as to leave only the adjusted for each station and even moderately strong negative portion of that signal (see Figure 19). The diode stations would clip in the final IF amplifier causing audio acts like an electronic check valve that only lets current distortion. AGC is accomplished by adjusting the DC pass in the same direction as the arrow (in the diode bias of the first IF amplifier to lower its gain as the signal symbol) points. When the diode is in conduction (On strength increases. Figure 19 shows that the audio at Condition), it will force capacitors C9 and C10 to charge the top of the volume control is actually “riding” on a to approximately the same voltage as the negative peak negative DC voltage when strong signals are of the IF signal. After conduction stops in the diode (Off encountered. This negative DC component corresponds Condition), the capacitors will discharge through to the strength of the incoming signal. The larger the resistors R11, R12 and the volume control. The signal, the more negative the component. At test point discharge time constant for this circuit must be small three (TP3), the audio is removed by a low pass filter, enough to follow the audio signal or high frequency R11 and C4, leaving only the DC component. Resistor audio distortion will occur. The discharge time constant R5 is used to shift the voltage at TP3 high enough to must be large enough, however, to remove the bias the base of transistor Q2 to the full gain position intermediate frequency (455kHz) and leave only the when no signal is present. Resistors R5 and R11 also audio at the volume control as shown in Figure 19. forward bias diode D1 just enough to minimize “On Condition” threshold voltage. Figure 19 -21-

23 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 23 ASSEMBLY INSTRUCTIONS - DETECTOR m F Lytic C6 - 100 (see Figure Da) Resistor R8 - 100 W Resistor W R5 - 27k (brown-black-brown-gold) (red-violet-orange-gold) T3 - IF Coil (black) T1 - IF Coil (yellow) TP5 - Test Point Pin TP3 - Test Point Pin (see Figure F) (see Figure F) m C15 - .001 F Discap C4 - 10 m F Lytic (marked 102) (see Figure Da) D1 - 1N4148 Diode W Resistor R11 - 3.3k (see Figure E) (orange-orange-red-gold) m C10 - .01 F Discap F Discap m F or .022 m C9 - .02 (marked 103) (marked 203 or 223) R12 - 2.2k W Resistor (red-red-red-gold) STATIC MEASUREMENTS (SW2 on the top [TR] position) AGC ZERO SIGNAL BIAS approximately 1.5 volts DC. If your reading varies more With the power turned OFF, connect the VOM to test point three (TP3) as shown in Figure 20. than 0.5 volts from this value, turn the power OFF and check the polarity of D1, and resistors R11 and R5. Also Check that the VOM is adjusted to read 9 volts DC and turn the power ON. The voltmeter should read check that transformer T1 is properly installed. GND TP10 Figure 20 T3 TEST as your battery voltage or power supply voltage. If not, With the power turned OFF, connect the positive lead of the VOM to TP5 and the negative lead to TP10. Make turn OFF the power and check that T3 is properly installed. sure that the VOM is set to read 9 volts DC and turn the power ON. The voltage on the VOM should be the same If you do not have an RF generator, go to Section 3. -22-

24 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 24 DYNAMIC MEASUREMENTS DETECTOR AND ACG TEST Turn the power OFF and connect the VOM and RF until the voltage at TP3 just starts to drop. This point is generator as shown in Figure 21. Set the VOM to called the AGC threshold with no IF gain. Make a note of the amplitude setting on the RF generator here: accurately read 2 volts DC and set the output of the RF generator for 455kHz, no modulaton, and minimum ____________. amplitude. Turn the power ON and slowly increase the amplitude of the 455kHz signal from the RF generator Turn the power OFF. Generator .02 F m Output Adjust GND TP10 GND TP10 Figure 21 If your RF generator does not have amplitude modulation or you do not have an oscilloscope, go to Section 3. SYSTEM CHECK Slowly adjust the amplitude of the RF generator output Connect equipment as shown in Figure 22. until you hear the 1kHz on the speaker. If this test fails, Set the RF generator at 455kHz, 1kHz at 80% turn the power OFF and check C11, R12, volume modulation and minimum output. Turn the power ON and put the volume control at full clockwise position. control, D1 and TP3. Generator Oscilloscope .02 m F Output Adjust GND TP10 Probe GND Figure 22 TP10 DETECTOR BANDWIDTH TEST Connect equipment as shown in Figure 22. Set the RF the RF output at 455kHz, but increase the modulation generator at 455kHz with 80% modulation at a frequency until the output drops to 0.28 Vpp. Record modulation frequency of 1kHz. Set the oscilloscope to the modulation frequency on the RF generator here: read 0.1 volts per division. Turn the power ON and put _________. the volume control at minimum. Increase the amplitude of the RF generator until the signal on the oscilloscope This frequency should be greater than 5kHz. Turn the is 4 divisions peak to peak. Check the signal to make power OFF. sure it is free of all distortion. Leave the frequency of -23-

25 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 25 SECTION 3 SECOND IF AMPLIFIER THEORY OF OPERATION The purpose of the SECOND IF AMPLIFIER is to The gain at 455kHz in the second IF amplifier is fixed by increase the amplitude of the intermediate frequency (IF) the AC impedance of the primary side of transformer T3, and at the same time provide SELECTIVITY. Selectivity and the DC current in Q3. The current in Q3 is set by is the ability to “pick out” one radio station while rejecting resistors R7, R9 and R10. Both C7 and C8 bypass the all others. The second IF transformer (T3) acts as a 455kHz signal to ground, making Q3 a common emitter bandpass filter with a 3dB bandwidth of approximately amplifier. The signal is coupled from the first IF amplifier 6kHz. The amplitude versus frequency response of the to the second IF amplifier through transformer T2. The second IF amplifier is shown in Figure 23. IF transformers not only supply coupling and selectivity, they also provide an impedance match between the collector of one stage and the base of the next stage. Both IF amplifiers are tuned to a frequency of 455kHz This match allows maximum power to transfer from one and only need to be aligned once when the radio is assembled. These amplifiers provide the majority of the stage to the next. gain and selectivity needed to separate the radio stations. .707 452kHz 458kHz 455kHz Figure 23 ASSEMBLY INSTRUCTIONS - SECOND IF AMPLIFIER R7 - 39k W Resistor T2 - IF Coil (White) (orange-white-orange-gold) TP4 - Test Point Pin Resistor W R9 - 10k (see Figure F) (brown-black-orange-gold) Q3 - 2N3904 Transistor NPN C7 - .02 m F or .022 m F Discap (see Figure A) (marked 203 or 223) R10 - 470 W Resistor m F Discap C8 - .02 m F or .022 (yellow-violet-brown-gold) (marked 203 or 223) -24-

26 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 26 STATIC MEASUREMENTS Q3 BIAS With the power OFF, connect the negative lead of your emitter of Q3 should be approximately 1 volt. If your VOM to any ground and the positive lead to the emitter reading is different by more than 0.5 volts, turn off the power and check your battery of power supply voltage. of Q3 as shown in Figure 24. Set the VOM to read 9 volts DC and turn ON the power. The voltage at the Also check components R7, R9, R10 and Q3. GND TP10 Figure 24 If you do not have an RF generator or oscilloscope, skip the following test and go to Section 4. DYNAMIC MEASUREMENTS AC GAIN With the power turned OFF, connect the oscilloscope and 4Vpp at the oscilloscope. After T3 is aligned, move the the RF generator to the circuit as shown in Figure 25. Set scope probe tip to the base of Q3 and record the peak the RF generator at a frequency of 455kHz, no to peak amplitude of the signal here: modulation and minimum amplitude output. Set the oscilloscope vertical sensitivity at 1 volt/division. The Vb=__________Vpp. scope probe must have an input capacitance of less than 50pF or it will detune transformer T3. Turn the Turn the power OFF. The AC gain of the second IF power ON and slowly increase the amplitude of the RF amplifier at 455kHz is equal to 4/Vb, and should be signal until you have 4 volts peak to peak on the greater than 100. If your gain is less than 100, check oscilloscope. Tune transformer T3 for a maximum output components C7, C8, R7, R9 and R10. Also, make sure while readjusting the RF generator amplitude to keep that transistor Q3 is properly installed. Oscilloscope Generator F m .02 Probe Output Adjust GND TP10 GND TP10 Figure 25 -25-

27 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 27 BANDWIDTH TEST Now increase the frequency of the RF generator past With the power OFF, connect your equipment as shown in Figure 26. Turn the power ON and adjust the RF the peak to a point where the signal drops to 0.707 of its peak value. Record that frequency point here: generator for 0.4Vpp at the cathode of D1. If necessary, realign transformer T3 for maximum output while FH=___________kHz. adjusting the output of the RF generator to maintain 0.4Vpp. Slowly decrease the frequency of the RF By subtracting the frequency of the lower 3dB corner generator until the signal drops to 0.707 of its peaked from the frequency of the higher 3dB corner you get the value or 0.28Vpp. Record the frequency of the RF BANDWIDTH of the second IF amplifier. Your results generator here: should be similar to the values shown in Figure 23. FL=___________kHz. Oscilloscope Generator F m .02 Output Adjust Probe GND TP10 GND TP10 Figure 26 SECTION 4 FIRST IF AMPLIFIER THEORY OF OPERATION The operation of the first IF amplifier is the same as for lowers the voltage across R6 and thus reduces the DC the second IF amplifier with one important difference. current through R6. Since all of the DC current from the The gain of the first IF amplifier decreases after the AGC emitter of Q2 must go through R6, the DC current in Q2 threshold is passed to keep the audio output constant at is therefore lowered. When the DC current in a transistor the detector and prevent overload of the second IF is lowered, its effective emitter resistance increases. The amplifier. This is accomplished by making the voltage on AC gain of transistor Q2 is equal to the AC collector load the base of transistor Q2, lower as the signal strength of Q2 divided by its effective emitter resistance. Raising increases. Since the voltage from base to emitter is fairly the value of the effective emitter resistance thus lowers constant, the drop in voltage at the base produces a the AC gain of Q2. similar drop in voltage at the emitter of Q2. This drop ASSEMBLY INSTRUCTIONS - FIRST IF AMPLIFIER Q2 - 2N3904 Transistor NPN W R4 - 1M Resistor (see Figure A) (brown-black-green-gold) Resistor R6 - 1k W TP2 - Test Point Pin (brown-black-red-gold) (see Figure F) m C5 - .02 m F or .022 F Discap (marked 203 or 223) -26-

28 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 28 STATIC MEASUREMENTS Q2 BASE BIAS voltage should be approximately 1.5 volts. If your circuit With the power turned OFF, reconnect your VOM to test point 3 (TP3) as shown in Figure 20. Set the VOM to fails this test, turn the power OFF and check Q2 and R6. read 2 volts DC accurately and turn the power ON. The Q2 CURRENT With the power turned OFF, connect the positive lead of should be approximately 0.8 volts. Since the current in Q2 is equal to the current in R6, I(Q2)=0.8/R6 or the VOM to the emitter of Q2. Connect the negative lead approximately 0.8 milliamps. of the VOM to TP10 and turn the power ON. The voltage If you do not have an RF generator or oscilloscope, skip the following test and go to Section 5. DYNAMIC MEASUREMENTS AC GAIN With the power turned OFF, connect the RF generator and generator amplitude in order to keep 4Vpp at TP4. Now the oscilloscope to your circuit as shown in Figure 27. move the oscilloscope probe to the base of Q2 and record Using a clip lead, short TP5 to R8 as shown in Figure 27. the peak to peak level of the 455kHz signal here: This short prevents the AGC from lowering the gain of the first IF ampifier. Set the RF generator to 455kHz, no Vb=____________Vpp. modulation, and minimum amplitude output. Set the oscilloscope for a vertical sensitivity of 1 volt/division and The AC gain of the first IF amplifier is equal to 4/Vb. The turn the power ON. Increase the amplitude output from AC gain of this amplifier should be greater than 100. DO the RF generator until approximately 4Vpp registers on NOT TURN THE POWER OFF. GO TO THE NEXT the oscilloscope. Tune the IF transformer (T2) to maximize TEST. the 455kHz at TP4. After tuning T2, adjust the RF AGC ACTION Move the oscilloscope probe back to TP4 and adjust the lead shorting TP5 to R8. The AGC should reduce the signal level at TP4 to approximately 0.3 volts. RF generator for 4Vpp if necessary. Remove the clip Oscilloscope Probe Generator .02 m F Wire lead GND TP10 or clip lead Output Adjust GND TP10 Figure 27 -27-

29 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 29 SECTION 5 MIXER AND OSCILLATOR THEORY OF OPERATION frequencies except those near 455kHz. T1 also couples In a superheterodyne type receiver the radio wave at the antenna is amplified and then mixed with the local the 455kHz signal to the base of Q2 to be processed by the IF amplifiers. oscillator to produce the intermediate frequency (IF). Transistor Q1 not only amplifies the RF signal but also The antenna and the oscillator coils are the only two simultaneously oscillates at a frequency 455kHz above resonant circuits that change when the radio is tuned for the desired radio station frequency. Positive feedback different stations. Since a radio station may exist 455kHz from the collector to the emitter of Q1 is provided by coil above the oscillator frequency, it is important that the L2 and capacitor C3. During the heterodyne process, antenna rejects this station and selects only the station the following four frequencies are present at the collector 455kHz below the oscillator frequency. The frequency of of Q1. the undesired station 455kHz above the oscillator is 1. The local oscillator frequency, LO. called the image frequency. If the selectivity of the antenna (Q factor) is high, the image will be reduced 2. The RF carrier or radio station frequency. sufficiently. 3. The sum of these two frequencies, LO + RF. 4. The difference of these two frequencies, LO - RF. The oscillator circuit must also change when the radio The “difference frequency” is used as the intermediate is tuned in order to remain 455kHz above the tuning of the desired radio station. The degree of accuracy in frequency in AM radios. The collector of Q1 also contains an IF transformer (T1) tuned only to the keeping the oscillator frequency exactly 455kHz above the tuning of the antenna is called tracking accuracy. difference frequency. This transformer rejects all ASSEMBLY INSTRUCTIONS - ANTENNA, MIXER AND OSCILLATOR Resistor R1 - 56k W (green-blue-orange-gold) L1 - Antenna with Holders (see Figures K & L) L2 - Oscillator Coil (red) F Discap F or .022 C2 - .02 m m Q1 - 2N3904 Transistor NPN (marked 203 or 223) (see Figure A) TP1 - Test Point Pin m F Capacitor C3 - .01 (see Figure F) (marked 103) W R2 - 12k Resistor C1 - Tuning Gang Capacitor (brown-red-orange-gold) 2 Screws M2.5 x 3.8mm Knob (dial) Resistor R3 - 3.3k W Screw M2.5 x 8mm (orange-orange-red-gold) Label (dial knob) (see Figure M) 4 Wire 3 Wire Figure K Determine if you have a three wire or four wire coil. Resistance White White measurements will be used to check the configuration of the coil. Slide one holder off the ferrite core of the antenna assembly. Then slide the coil off the the ferrite core. Measure the resistance of the coil. Your readings should match the approximate values as shown. W R=9 - 11 W R=9 - 11 Note: If the end of a wire from the antenna should break off, } strip the insulation off the end with a hot soldering iron. } Black Lay the wire down on a hard surface and stroke the R=1 - 1.5 W Black Red } wire with your iron. The insulation should come The soldering CAUTION: off very easily. Red iron will burn the hard surface that you W R=1 - 1.5 } are working on. Green -28-

30 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 30 Assemble it to the PC board as shown below. 3 Wire Type Antenna Mount the antenna assembly to the PC board. Solder the 3 colored wires to the PC board. Wire A (red) to the hole marked “3”. r r Put the tab of the first holder into the right hole and twist the tab 90°. r Wire B (black) to the hole marked “2”. r Put the tab of the second holder into the left Wire C (white) to the hole marked “1”. r hole and twist the tab 90°. C (white) B (black) A (red) Slide the ferrite core through the holders. r Slide the antenna coil through the ferrite core. r If the end of a wire from the antenna should Note: break off, strip the insulation off the end with a hot Tabs 4 Wire Type Antenna soldering iron. Lay the wire down on a hard Solder the 4 colored wires to the PC board. surface and stroke the wire with your iron. The insulation should come off very easily. Wire A (green) to the hole marked “3”. r r Wire B (red and black twisted together) to the The soldering iron will burn the hard CAUTION: hole marked “2”. surface that you are working on. Wire C (white) to the hole marked “1”. r Twisted together B C (white) Punch out one antenna shim from the front flap of the box. Black Insert the cardboard antenna shim between the ferrite core and the antenna coil. This will temporarily hold the Red coil in place. A (green) Tabs OR C (white) B Twisted together Black Figure L A (green) Red M2.5 x 8mm Your kit may contain a 3 lead or a 4 lead Fasten the knob to the Screw capacitor. Bend the leads as shown. Fasten C1 shaft of the capacitor Knob into place on the top side of the PC board with with one M2.5 x 8mm two M2.5 x 4mm screws. screw. Knob post C1 Turn the dial fully clockwise. Remove the protective backing from the label and align the 1600 with the arrow on the 3 Leads Screw holes PC board. Solder leads to pads 4 Leads Figure M -29-

31 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 31 PC Board Stand Insert the PC board into the stand as shown. Figure N STATIC MEASUREMENTS Q1 BIAS TP1 should be 1.6 volts. If the voltage in your circuit With the power turned OFF, connect the VOM to your differs by more than 0.5 volts, leave the power ON and circuit as shown in Figure 28. Connect a clip lead from test point two (TP2) to the collector of Q1. This short check the battery voltage. If the battery voltage is greater than 8.5 volts, turn the power OFF and check prevents Q1 from oscillating. Set the VOM to read 2 volts DC accurately and turn the power ON. The DC voltage at components R1, R2, R3 and Q1. Wire lead or clip lead GND TP10 Figure 28 If you do not have an oscilloscope, go to the Final Alignments With No Test Equipment Section. -30-

32 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 32 DYNAMIC MEASUREMENTS OSCILLATOR CIRCUIT wave. The frequency of the sine wave should change With the power turned OFF, connect the oscilloscope to when capacitor C1 is turned. If your circuit fails this test, Set the oscilloscope for the circuit as shown in Figure 29. a vertical sensitivity of 1 volt/division and turn the power turn the power OFF and check components Q1, C1, C2, ON. The oscilloscope should display a low voltage sine C3, L1 and L2. Oscilloscope Figure 29 GND TP10 If you do not have an RF generator, go to the Final Alignments with No Test Equipment Section. FINAL ALIGNMENTS IF BANDWIDTH With the power turned OFF, connect the RF generator and After IF alignment, lower the frequency from the RF the oscilloscope to your circuit as shown in Figure 30. generator until the reading on the VOM drops to 0.707 Short TP2 to the collector of Q1 with a clip lead to “kill” of its peaked value. Record the frequency of this lower the local oscillator. Set the RF generator at a frequency 3dB corner here: of 455kHz, modulation of 400Hz 80%, minimum Fl=____________kHz. amplitude output. Set the oscilloscope to read 0.1Vpp Increase the RF generator frequency past the peak to and turn the power ON. Increase the amplitude of the the upper 3dB corner and record that frequency here: RF signal until the oscilloscope registers 0.5Vpp. Align Fh=____________kHz. transformers T3, T2 and T1 for the maximum AC reading on the oscilloscope. Decrease the amplitude of the The bandwidth of the IF amplifiers is BW=Fh - Fl. IF signal from the RF generator to restore 0.5Vpp on the bandwidth should be between 1 to 2kHz. This bandwidth oscilloscope. Repeat the last two steps until no change will widen as the AGC is approached. in the peak at the oscilloscope is noticed. Oscilloscope Generator .02 m F Probe Output Adjust GND TP10 GND Wire lead TP10 Figure 30 or clip lead -31-

33 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 33 SETTING OSCILLATOR RANGE With the power turned OFF, connect the equipment to the Oscillator trimmer Antenna trimmer circuit as shown in Figure 30. DO NOT connect the clip lead from TP2 to Q1. Set the RF generator at 540kHz, 400Hz 80% modulation, and a low level of output. Turn 3 Leads the tuning capacitor fully counter-clockwise. Turn the power ON and a 400Hz tone should be heard coming from the speaker. Tune the oscillator coil (L2) for a peak on the oscilloscope. Adjust the RF generator output Antenna trimmer Oscillator trimmer during this process to maintain a peak at 0.5Vpp or less. After peaking L2, set the RF generator frequency to 1600kHz and turn the tuning capacitor (C1) fully 4 Leads clockwise. A 400Hz tone should be heard coming from the speaker. Tune the oscillator trimmer capacitor on the back of C1 for a peak on the oscilloscope (see Figure 31). Figure 31 After peaking the oscillator trimmer capacitor, return the verify this alignment by measuring the frequency at the emitter of Q1 for both ends of the tuning capacitor (C1). RF generator to 540kHz, and capacitor C1 to the fully counter-clockwise position and readjust L2. Repeat the Be careful not to mistune the oscillator during this last few steps until both settings of the oscillator are measurement. A coupling capacitor of 82 picofarads or correct. This process sets the oscillator range at 995kHz less to the frequency counter is recommended. to 2055kHz. If a frequency counter is available, you may ANTENNA ALIGNMENT With the power turned OFF, connect test equipment to generator to 1400kHz and adjust C1 until a 400Hz tone your circuit as shown in Figure 32. Set the RF generator can be heard coming from the speaker. Carefully peak the at 600kHz, 400Hz 80% modulation, moderate signal reading on the oscilloscope by adjusting the frequency of strength. Set the oscilloscope to read 0.5Vpp and turn the the RF generator. Now tune the antenna coil to this power ON. Turn C1 fully counter-clockwise, then slowly frequency by adjusting the antenna trimmer on the back turn C1 clockwise until a 400Hz tone can be heard coming of C1 (see Figure 31). This process should be repeated from the speaker. Slowly slide the antenna coil back and until both settings of the antenna track the oscillator forth on the ferrite rod to obtain a peak on the tuning. Once the antenna is properly aligned, carefully oscilloscope. For maximum signal, your location of the apply candle wax or glue to the antenna coil and ferrite antenna coil may have to be on the end of the ferrite rod rod (as shown in Figure 33). (as shown in Figure 33). Change the frequency of the RF Oscilloscope Close to antenna Probe Generator Output Adjust GND TP10 GND Figure 32 TP10 Holders Wax Coil Figure 33 Wax -32-

34 AM-550CK_REV-A_010416.qxp 1/19/16 9:04 AM Page 34 AM ALIGNMENT WITH NO TEST EQUIPMENT It is best to use an earphone for this alignment their broadcast frequency is announced. If no stations procedure. Rotate the tuning knob fully counter- are present at the low side of the AM band, adjust L2 clockwise and place the label on the knob with the white until a station is heard. Once a station is found and its arrow pointing at the 540kHz marking. broadcast frequency is known, rotate the dial until the white pointer is aligned with that station’s frequency With an alignment tool or screwdriver, turn coils L2, T1, marking on the dial. Adjust L2 until the station is heard. T2 and T3 fully counter-clockwise until they stop. DO Tune the radio until a station around 1400kHz is heard. NOT FORCE THE COILS ANY FURTHER. Turn each It may be necessary to listen to the station until their coil in about 1¼ to 1½ turns. Set the antenna coil about broadcast frequency is announced. If no stations are 1/8” from the end of its ferrite rod. Refer to Figure L on present at the high end of the AM band, adjust the page 29. oscillator trimmer on the back of the gang. Once a station is found and its broadcast frequency is known, Turn the power ON and adjust the volume to a rotate the dial until the white pointer is aligned with that comfortable level. Tune the dial until a weak station is station’s frequency marking on the dial. Adjust the heard. If no stations are present, carefully slide the oscillator trimmer located on the back of the gang until antenna back and forth on its ferrite rod and retune the a station is heard. Repeat these steps until the oscillator dial if necessary. With an alignment tool or screwdriver, alignment is optimized. This procedure set the oscillator adjust T1 until the station is at its loudest. Reduce the range at 995kHz to 2055kHz. volume control if necessary. Adjust T2 until the station is at its loudest and reduce the volume control if Tune the radio for a station around 600kHz. Carefully necessary. Adjust T3 until the station is at its loudest and slide the antenna back and forth until the station is at its reduce the volume if necessary. Retune the radio for loudest. Tune the radio for a station around 1400kHz. another weak station and repeat this procedure until Adjust the antenna trimmer located on the back of the there is no more improvement noticed on the weakest gang until the station is at its loudest. Repeat these possible station. This procedure peaked the IF amplifiers steps until the antenna alignment is optimized. This to their maximum gain. procedure set the antenna to “track” the oscillator. Once the antenna is properly aligned, carefully apply candle Tune the radio until a known station around 600kHz is wax or glue the antenna coil to the ferrite rod to prevent found. It may be necessary to listen to the station until it from moving (as shown in Figure 33). DC Voltages The voltage readings below should be used in troubleshooting the AM radio. Measure the voltage on transistors Q4 - Q6 with switch SW2 in the top position. When measuring the voltage on the IC, make sure the switch SW2 is in the down position. Q6 B 1.5V Q1 B 5.8V E 1.0V E 5.2V C 8.9V C 9.0V Test Conditions 1. Volume control set to minimum. Q2 B 1.4V Q7 B 4.6V 2. Connect a jumper wire between capacitor C2 (side that E 0.7V E 5.2V goes to red lead of coil L1) to negative battery. C 8.9V C 0.0V 3. Battery voltage: 9.0V 4. All voltages are referenced to circuit common. Q3 B 1.7V U1 1 - 1.3V 5. Voltage reading can vary + 10%. E 1.0V 2 - 0 C 9.0V 3 - 0 4 - 0 B 5.7V 5 - 4.5V Q4 E 5.2V 6 - 9V C 8.3V 7 - 4.6V 8 - 1.3V Q5 B 8.3V E 9.0V C 5.8V -33-

35 AM-550CK_REV-A_010416.qxp 1/19/16 9:05 AM Page 35 AM-550CK RADIO BAFFLE . After you have completed the radio and it operates satisfactorily, you may want to install a baffle : NOTICE Keep the box the kit came in 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. If it does not want to come out easily, use a knife to cut the holding tabs. When a speaker is not enclosed, sound waves can travel in all directions. As a speaker moves outward, it creates positive pressure on the air in front of it and negative pressure on the rear. At low frequencies, out of phase front and rear waves mix causing partial or total cancellation of the sound wave. The end result is a speaker less efficient and distorted. To eliminate the low frequency cancellation, a speaker is placed inside an enclosure. Now the front sound waves are prevented from traveling to the back. The speaker will now compress and decompress air inside, increasing its resonant frequency and Q relative to the free air values. This type of effectively air-tight box is called an Acoustic Suspension . Screw M1.8 x 7mm AM-550C Kit Carton Nut M1.8 brown side Baffle 2. Bend the four flaps upward as shown. 1. Start at one edge and carefully remove the baffle from the bottom of the kit box. 3. Bend the top side upward as shown. 4. Bend the two sides upward. Attach the 5. Bend the bottom side upward and three sides using scotch tape or glue attach it to the other sides using scotch (Elmer’s, Duco Cement, or other). tape or glue. Bend the two mounting flaps as shown. 6. Back View M1.8 x 7mm Screw Seal M1.8 Nut M1.8 x 8mm Screw (from battery holder) Remove the nut from the top M1.8 x 7mm screw. Insert the baffle as shown in Step 6. Insert an M1.8 x 7mm screw and fasten down r the baffle with two M1.8 nuts as shown in Step 6. : To make an air tight seal, place a bead of seal between the PC board and the baffle. Optional -34-

36 AM-550CK_REV-A_010416.qxp 1/19/16 9:05 AM Page 36 SCHEMATIC DIAGRAM ® ELENCO 150 Carpenter Avenue ● Wheeling, IL 60090 (847) 541-3800 ● Website: www.elenco.com ● e-mail: [email protected]

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