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HR40 • 12
capacitor is a first step in setting up the resonant frequency of the SA602’s
internal oscillator, using the resonant LC circuit to be created along with
C1, C3 and L1.
12. Install C1, 100pF disc capacitor (marked 100 or 101K).
13. Install C3, .001µF disc capacitor (marked 102 or .001 or 1nF).
14. Install L2, shielded oscillator coil (marked K6883 or K6886).
15. Install C4, 100pFdisc capacitor (marked 100 or 101). C4 adds variable
capacitance of the varactor tuning network to the oscillator circuit already
formed by L2, C1, C2 and the SA602.
16. Install D1, the 1N4002 diode, making sure that the cathode or banded
end is oriented towards the back of the PC board. This diode performs the
function of a varactor diode. A varactor diode acts like a variable capacitor
whose capacitance is controlled by the voltage across it. There is nothing
fancy about the varactor diodes, so we are using a common rectifier diode
as a varactor.
17. Install R5, 10k ohms (brown-black-orange)
18. Install R2, 10k potentiometer tuning control.
19. Install R3, 10k potentiometer volume control. This control varies the
level of audio from pin 4 of the SA602 to the LM386 audio amplifier.
20. Using a scrap piece of wire, snipped from an installed component,
install JMP-1. Jumpers are required sometimes in PC board layout to
make a connection that has to cross over other PC-board traces.This
particular jumper brings 9 volts from the power switch to the long circuit
trace supplying voltage to the entire circuit. Notice how the jumper crosses
over the other traces leading from the volume control.
21. Install S1, the power switch.
22. Install the 9-volt battery snap connector, making sure that the red (+)
and black (-) leads are correctly installed.
23. Install C7, .01µF disc capacitor (marked 103 or .01 or 10nF).
24. Install C8, a small 4.7-10µF electrolytic capacitor. Observe correct
polarity.
25. Install R6, 10K ohm resistor (brown-black-orange).
26. nstall U2, the LM386 audio amplifier IC chip. Just like the SA602, you
must correctly position the notched or banded end.
27. Install C12, 100-220µF electrolytic capacitor; observe polarity. This
capacitor couples the output of the LM-386 to the speaker jack.
28. Install C9, 4.7-10µF electrolytic capacitor; observe polarity.