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SS70A • 10
without "straining" the leads. Solder all three connections securely.
16. Install R12, 1K ohm (brown-black-red).
17. Install R9, 470 ohm (what colors were those?!) (yellow-violet-brown).
18. Install C12, a 10 uF electrolytic capacitor. This component is
"polarized" and must be oriented correctly before soldering. The positive
or ( + ) points are clearly marked on the PC board layout diagram. Study
the style and markings of the capacitors supplied in your kit. Generally,
electrolytic capacitors indicate the negative, or ( - ) lead with a black
edge strip or a ( - ) marking. Be alert about polarity throughout assembly!
19. Install Q1, a 2N3904 transistor. Be sure to face the flat side as
shown in the diagram.
20. Install R7, 1K ohm resistor (brown-black-red).
21. Install C5, 10 uF electrolytic capacitor. Again, this component is
polarized so check the parts layout for correct orientation.
22. Install jumper JMP2 (formed from a scrap component lead).
23. Install R5, 470 ohm (yellow-violet-brown).
24. Install C14, a .01 uF disc capacitor (marked .01 or 10 nf or 103).
25. Install U2 the LM380 audio amplifier IC. Notice that one end of the
chip is marked with a notch, dot, or band. Check the parts diagram for
correct placement. Before soldering, ensure all pins have made it
through the board. (It’s not much fun removing a chip because one pin is
bent under!)
26. Install C15, a 1000 uF electrolytic capacitor. Be sure to orient it
correctly, as electrolytic caps can explode if installed backwards! This
capacitor acts to filter the supply voltage for noise free audio.
27. Install capacitor C10, the 100-220 uF electrolytic. Note the polarity on
the parts placement diagram.
28. Install C13, a .1 uF disc capacitor (marked .1 or 104).
29. Install R13, 2 ohm (red-black-gold). Components C13 and R13 keep
the audio output from becoming unstable with different speaker loads.
30. Install J4, the 3 pin header strip. Later we’ll use a small jumper block
to enable switching between line or speaker level audio output without
having to remove and resolder jumpers.
31. Install jumper JMP4.
You’ve just completed the output paths for both the TX and RX portions of
the circuit. Take a break and recheck your work. It’s also a good time to take
a look at the schematic diagram and follow through what we’ve done.
Moving on, we'll build the "heart" of your scrambler unit, containing the
MX128 IC and associated components. Since the majority of the work is