Ramsey Electronics HR40 - Manual (Page 12)

HR40
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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.
ˆ 12. Install C1, 100pF disc capacitor (marked 100 or 101K).
ˆ 13. Install C3, .001µF disc capacitor (marked 102 or .001 or 1nF).
ˆ 14. Install L2, shielded oscillator coil (marked K6883 or K6886).
ˆ 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.
ˆ 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.
ˆ 17. Install R5, 10k ohms (brown-black-orange)
ˆ 18. Install R2, 10k potentiometer tuning control.
ˆ 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.
ˆ 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.
ˆ 21. Install S1, the power switch.
ˆ 22. Install the 9-volt battery snap connector, making sure that the red (+)
and black (-) leads are correctly installed.
ˆ 23. Install C7, .01µF disc capacitor (marked 103 or .01 or 10nF).
ˆ 24. Install C8, a small 4.7-10µF electrolytic capacitor. Observe correct
polarity.
ˆ 25. Install R6, 10K ohm resistor (brown-black-orange).
ˆ 26. nstall U2, the LM386 audio amplifier IC chip. Just like the SA602, you
must correctly position the notched or banded end.
ˆ 27. Install C12, 100-220µF electrolytic capacitor; observe polarity. This
capacitor couples the output of the LM-386 to the speaker jack.
ˆ 28. Install C9, 4.7-10µF electrolytic capacitor; observe polarity.