Ramsey Electronics SR2, User Manual

Page: 13 / 28

SR2 – 13
We will now begin constructing the local oscillator section.
ˆ 5. Install C22, one of the 10µF electrolytic capacitors. Electrolytic
capacitors have a right and wrong way to be installed. Usually,
capacitors have a wide stripe which indicates their negative lead and the
PC board or Parts Layout Diagram will show the positive side of the
capacitor's installation hole. Be sure to place the ( + ) capacitor lead
into the PC board ( + ) hole and the ( - ) lead into the ( - ) hole before
soldering.
ˆ 6. Install D3, the varactor diode, marked MVAM108. This part looks
like a transistor except that it only has two leads. It must be installed
with the proper polarity to work correctly. You will note that it has a flat
side. Be sure to look at the PC board silkscreen or parts layout diagram
for proper placement of the flat side. Once you have correctly placed
the part, solder the leads.
ˆ 7. Install R23, 10K ohm [brown-black-orange].
ˆ 8. Install Q3, an NPN transistor, [marked 2N3904]. This part is also
oriented by the flat side so check your parts layout diagram for proper
placement. Bend the center lead out until it fits in the board and seat
the part as close to the PC board as possible. Solder all three leads.
ˆ 9. Install C17, a 100 pF capacitor [marked 100, 101, or 100K].
ˆ 10. Install C25, .001µF disc capacitor [marked .001, 102, or 1nF].
ˆ 11. Install C19, a .1µF ceramic disc capacitor [marked .1 or 104].
ˆ 12. Install C18, another .1µF ceramic disc capacitor [marked .1 or 104].
ˆ 13. Install R20, 100K ohms [brown-black-yellow].
ˆ 14. Install R25, a 270 ohm resistor [red-violet-brown].
ˆ 15. Install R19, 10K ohms [brown-black-orange].
ˆ 16. Install R24, 1K ohms [brown-black-red].
ˆ 17. Install C26, the 1000µF electrolytic capacitor. Remember to check
the polarity and install properly before soldering.
ˆ 18. Install R22, 270 ohms [red-violet-brown].
ˆ 19. Install C20, .001µF disc capacitor [marked .001, 102, or 1nF].
ˆ 20. Install C21, another .001µF disc capacitor [marked .001, 102, or
1nF].
Before installing T3, the shielded can inductor [marked 42IF123] we must
make a modification to the part. It's time for a little "destruction"! (If you