Elenco Electronics AM-780K Assembly And Instruction Manual
AM RADIO KIT
MODEL AM-780K
Assembly and Instruction Manual
Elenco®Electronics, Inc.
Copyright © 2007, 1999 by Elenco®Electronics, Inc. All rights reserved. Revised 2007 REV-F 753108
No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.
PARTS LIST
If you are a student, and any parts are missing or damaged, please see instructor or bookstore.
If you purchased this kit from a distributor, catalog, etc., please contact Elenco
®
Electronics (address/phone/email is at the back of this manual) for additional assistance, if needed. DO NOT contact your place of purchase
as they will not be able to help you.
RESISTORS
Qty. Symbol Value Color Code Part #
1 R6 10Ω 5% 1/4W brown-black-black-gold 121000
1 R4 150Ω 5% 1/4W brown-green-brown-gold 131500
1R2 3.3kΩ 5% 1/4W orange-orange-red-gold 143300
1R5 8.2kΩ 5% 1/4W gray-red-red-gold 148200
1 R1 100kΩ 5% 1/4W brown-black-yellow-gold 161000
1 R3 Potentiometer 50kΩ & 192522
switch w/ Nut & Washer
CAPACITORS
Qty. Symbol Value Description Part #
1 C2 Variable Tuning Capacitor 211677
1C1 .01μF Discap (103) 241031
2 C3, C9 .047μF Discap (473) 244700
3 C4, C5, C8 10μF Electrolytic Radial 271045
2 C6, C7 470μF Electrolytic Radial 284743
SEMICONDUCTORS
Qty. Symbol Value Description Part #
2 D1, D2 1N4148 Semiconductor Silicon Diode 314148
1 IC2 LM-386 Integrated Circuit 330386
1 IC1 484 / 7642 Integrated Circuit 33K484
MISCELLANEOUS
PARTS IDENTIFICATION
Qty. Description Part #
1 Antenna with Holders 484004
1 PC Board 517053
1 Battery Holder 590096
1 Speaker 8Ω 590102
1 Knob for Potentiometer 622017
1 Knob for Variable Capacitor 622030
1 Screw 2-56 x 5/16” 641231
Qty. Description Part #
3 Screw #3 x 5/32” 641310
1 Nut 2-56 644201
1 Socket IC 8-pin 664008
1 Label 720421
1 Speaker Pad 780128
4 Wire 2” 834011
1 Solder Lead-free 9LF99
-1-
RESISTORS SEMICONDUCTORS
Resistor
Diode
484 / 7642
LM-386
IC Socket
Antenna with Holders
MISCELLANEOUS
Speaker
50kΩ Potentiometer
and Switch
CAPACITORS
Discap
Electrolytic
Radial
Tuning
Battery Holder
Knob (dial)
Knob
(pot)
Label
Screw
#3 x 5/32”
Nut
2-56
Screw
2-56 x 5/16”
Speaker Pad
-2-
• 9V Battery
• 25 or 30 watt Soldering Iron
• Small Phillips and Slotted Screwdrivers
• Long Nose Plier
• Side Cutters
IDENTIFYING RESISTOR VALUES
Use the following information as a guide in properly identifying the value of resistors.
BANDS
METRIC UNITS AND CONVERSIONS
Abbreviation Means Multiply Unit By Or
p Pico .000000000001 10
-12
n nano .000000001 10
-9
μ micro .000001 10
-6
m milli .001 10
-3
– unit 1 10
0
k kilo 1,000 10
3
M mega 1,000,000 10
6
1. 1,000 pico units = 1 nano unit
2. 1,000 nano units = 1 micro unit
3. 1,000 micro units = 1 milli unit
4. 1,000 milli units = 1 unit
5. 1,000 units = 1 kilo unit
6. 1,000 kilo units = 1 mega unit
You Will Need:
IDENTIFYING CAPACITOR VALUES
Capacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or μF (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.
Second Digit
First Digit
Multiplier
Tolerance*
Note: The letter “R”
may be used at times
to signify a decimal
point; as in 3R3 = 3.3
103K
100V
The letter M indicates a tolerance of +20%
The letter K indicates a tolerance of +
10%
The letter J indicates a tolerance of +5%
Maximum Working Voltage
The value is 10 x 1,000 =
10,000pF or .01μF 100V
*
Electrolytic capacitors have a positive
and a negative electrode. The
negative lead is indicated on the
packaging by a stripe with minus
signs and possibly arrowheads.
Warning:
If the capacitor is
connected with
incorrect polarity, it
may heat up and
either leak, or cause
the capacitor to
explode.
Polarity
Marking
BAND 1
1st Digit
Color Digit
Black 0
Brown
1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Gray 8
White 9
BAND 2
2nd Digit
Color Digit
Black 0
Brown 1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Gray 8
White 9
Multiplier
Color Multiplier
Black 1
Brown 10
Red 100
Orange 1,000
Yellow 10,000
Green 100,000
Blue 1,000,000
Silver 0.01
Gold 0.1
Resistance
Tolerance
Color Tolerance
Silver ±10%
Gold ±5%
Brown ±1%
Red ±2%
Orange ±3%
Green ±0.5%
Blue ±0.25%
Violet ±0.1%
1
2 Multiplier Tolerance
Multiplier
For the No. 0 1 2 3 4 5 8 9
Multiply By 1 10 100 1k 10k 100k .01 0.1
INTRODUCTION
-3-
Radio
Frequency
Amplifier
Detector
Audio
Amplifier
Figure 1
IC 484 / 7642
IC LM-386 Speaker
The Model AM-780K AM Radio can be best
understood by analysis of the block diagram shown
in Figure 1.
The coils on the ferrite rod antenna (L1 and L2) and
the variable capacitors (C2) make up a “tuned circuit”
(see schematic diagram below). It is a very selective
filter. The frequency is selectable over a certain range
by adjusting the tuning capacitor. The selectable
signal is passed into IC1 (integrated circuit 484/7642)
where it is amplified and then detected. The 484/7642
is a monolithic integral circuit equal to a ten transistor
tuned radio frequency circuit. The resistor R2 and the
capacitor C3 set the automatic gain control of IC1.
The 484/7642 requires a low voltage power supply
(1.1 - 1.8V). The voltage drop across diodes D1, D2,
and resistor R4 is the correct supply voltage to IC1.
The output from a diode detector of the 484/7642 is
typically 40 - 60mV. This audio signal is too weak to
drive a speaker directly. Capacitor C3 filters out the
radio frequency component of the signal, leaving a
clean audio signal.
The amount of gain control is varied by potentiometer
R3, which also varies the audio level and
consequently the volume. Capacitor C5 couples the
audio signal from the volume control to the input of
the audio amplifier. Our kit uses the standard design
for the audio amplifier on the base of the integral
circuit LM-386. To make the LM-386 a more versitile
amplifier, two pins (1 and 8) are provided for gain
control. With pins 1 and 8 open, the gain at 20, the
capacitor will go up to 200. Capacitor C7 blocks the
DC from the speaker while allowing the AC to pass.
SCHEMATIC DIAGRAM AM-780K
The AM-780K is a tuned radio frequency (TRF)
receiver of the standard AM (amplitude modulation)
broadcast frequencies (550kHz - 1600kHz). Easyto-build, using only two integral circuits (IC).
Assembly of your AM-780K AM Radio Kit will prove
to be an exciting project and give you much
satisfaction and personal achievement. Care must
be given to identifying the proper components and
in good soldering habits. Above all, take your time
and follow these easy step-by-step instructions.
Remember, “An ounce of prevention is worth a
pound of cure”. Avoid making mistakes and no
problems will occur.
Construction Time: About 3 Hours.
WHAT IT IS
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