WD2XES LF 5 WATT AMPLIFIER
This small linear amplifier has been useful for low-power testing. It would also make a good driver
for a higher-powered amplifier that required real driving power. The present model is built in a cast
aluminum case, and is used with an external power supply. My bench supply provides 30 VDC, good enough
for a clean 8 watts. The capacitors are all rated at 50 volts or more, and I plan to run it from a 40
VDC supply, assuring the full 10 watts. At 24 VDC, the amp is clean to 6 watts output.
The 50k trimpot on the 2N2222A was used to center the LM2876 output at 1/2 of the supply
voltage. The 1k input pot has a knob, and becomes the power level control. I suggest using a low-pass
"T" network at the output for extra harmonic rejection and better stability with a real-world antenna
load. The LM2876 can be bolted directly to the case or a grounded heat sink. Pin 8 is a Mute pin, and
could be used for keying if needed. See the National data sheet for more information.
Change on 11 Dec 2005: The output transformer was changed to 5T:15T, with the primary and secondary windings interleaved. This increased the power output to the figures listed above.
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