Ramsey Electronics SR2, User Manual

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SR2 – 16
jumped ahead and installed T3, we've got bad news for you). Before this
shielded transformer can be installed, its internal capacitor needs to be
removed. Looking at the underside of this transformer, you'll see a tubular
part, probably white with a brown band, somewhat like the resistors in this
kit. This is brittle and easily crushed with any sharp object that can be
pressed against it with mild force (small nail, nutpick, small screwdriver).
You'll find this capacitor will easily disintegrate into particles. DO NOT crush
the capacitors in the other two inductors!
ˆ 21. After crushing the internal capacitor, install T3. The part fits in the
board only one way. Solder all pins.
That completes assembly of the local oscillator section except for two parts.
You may notice that we skipped over C15 and C16 while installing the other
parts in the area. The reason is that you will have to decide the frequency
range you’re trying to receive to know what value capacitors to install. We’ll
leave that until the end of the assembly process.
We’ll now move on to the RF section of your SR2 kit. The next few parts
form an input filter and mixer section, to combine the RF input with the L.O.
section just built. The output of the mixer is the IF, from which we’ll extract
the final audio. But let’s not get ahead of ourselves.
ˆ 22. Install L1, 1µH inductor [looks like a fat resistor with brown-black-
gold bands].
ˆ 23. Install L2, the other 1µH inductor [looks like a fat resistor with
brown-black-gold bands].
ˆ 24. Install C3, .001µF disc capacitor [marked .001, 102, or 1nF].
ˆ 25. Install C2, 330 pF disc capacitor [marked 330 or 331].
ˆ 26. Install C1, .001µF disc capacitor [marked .001, 102, or 1nF].
ˆ 27. Install R13, 1K ohms [brown-black-red]. R13 isn’t part of the RF
section but is easier to install now, while we’re in the area.
ˆ 28. Install R3, 1K ohm [brown-black-red]. Watch that third color band
as red is easily confused with orange!
ˆ 29. Install Q1, another of the NPN transistors [marked 3904]. Observe
correct orientation of the flat side when placing this part.
ˆ 30. Install C10, .1µF ceramic disc capacitor [marked .1 or 104].
ˆ 31. Install R12, 1M ohm [brown-black-green]. C10 and R12 are part of
the bias circuit for the audio amplifier, U1. Like R13, it is easier to install
these parts now.
ˆ 32. Install C30, 10pF [marked 10].