Ramsey Electronics FM25B, Assembly And Instruction Manual

Page: 15 / 36

FM25B
•
15
ˆ 16. Install J4, the other stereo jack.
Now we’ll install some electrolytic caps. Electrolytic capacitors have a right and
wrong way to be installed. Usually, capacitors have a wide black 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. Observe correct polarity when installing the electrolytic capacitors.
ˆ 17. Install C32, 1000 µF electrolytic capacitor. Remember polarity!
ˆ
18. Install C30, 10 µF electrolytic capacitor. The next two parts will be
identical, and will have the same polarity so be careful with this first one.
ˆ 19. Install C29, another 10 µF electrolytic capacitor.
ˆ 20. Install C28, yet another 10 µF electrolytic capacitor.
ˆ 21. Install C40, 100 pF disc capacitor (marked 100 or 101).
ˆ
22. Install C39, 100 pF disc capacitor (marked 100 or 101).
ˆ 23. Install C37, 75 pF disc capacitor (marked 75 or 75K).
ˆ 24. Install C38, 47 pF disc capacitor (marked 47).
ˆ 25. Install L4, a prewound spring style inductor.
ˆ 26. Install L2, the other prewound spring style inductor.
ˆ 27. Install C34, 47 pF disc capacitor (marked 47).
ˆ 28. Install C33, .001 µF disc capacitor (marked .001, 102 or 1nF).
ˆ 29. Install C24 and C27, 3300 pF (marked 332 or 0.0033). For use in
Europe, use 2200 pF capacitors (marked 222 or .0022). These capacitors
set the pre-emphasis characteristics for the FM25B. Pre-emphasis is a
technique used in FM transmitters to increase the high frequency signal to
noise ratio.
ˆ 30. Install C25, 150 pF (marked 150 or 151).
ˆ 31. Install C22, 150 pF (marked 150 or 151).
ˆ 32. Install R25, 1k ohm trimmer pot (marked 102). This potentiometer ad-
justs the final RF output.
ˆ 33. Install C31, .001 µF disc capacitor (marked .001, 102 or 1nF).
ˆ 34. Install R26, 120 ohms (large, 1 watt, brown-red-brown). You’ll notice
that this part is quite a bit bigger than the other resistors in your kit. This is
a 1 watt resistor and the others are 1/4 watt. That means this resistor can
dissipate 1 watt of power if needed.
ˆ 35. Install C26, .01 µF disc capacitor (marked .01 or 103 or 10 nF).