How to Convert CB Linears for HF
Citizen's band, or CB, amplifiers can be converted to operate on a higher high frequency, or HF, by replacing the transmitter crystal and inserting a PNP keying transistor. A CB linear operates at a frequency of about 26 to 27 megahertz in the U.S., which is within the HF band. HF broadcasting -- also known as shortwave -- operates at 3 to 30 MHz. You can perform a conversion to raise the frequency that the CB linear operates at, making the range 28 to 30 MHz. While the U.S. Federal Communications Commission states that professional radio stations must not raise the power output of CB units, any amateur radio operator is permitted to convert a home CB radio to a ham frequency.
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Things You'll Need
- Non-metallic screwdriver
- Master link pliers
- 10.610 MHz X11 crystal
- PNP keying transistor
- Soldering iron
Instructions
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Replace the Transmitter Crystal
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1
Unplug the amplifier from the power supply. Disassemble the amp by removing the four screws at the front of the unit with a screwdriver. Lift the lid off the box. The three main sections of the amp should be aligned from left to right in the box as such: tubes and printed circuit board; transformer and power supply; and pi-greek and switches.
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2
Isolate the circuit board and identify the transmitter crystal -- a raised silver elliptical component on the circuit board that is located at the center of the top of the board and to the right of the crystal oscillator. Turn the circuit board upside down, and cut the soldered wire holding the crystal in place, using pliers. Turn the circuit board faceup, and remove the crystal by teasing the wires through the holes with pliers.
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3
Replace the transmit crystal with a 10.160MHz X11 crystal. To do this, insert the crystal's wires into the holes where the previous transmit crystal was positioned. Turn the circuit board upside down. Heat the soldering iron, and daub the crystal wires that are poking out of the back of the board with the iron until they melt. Leave the soldered wire to cool for several minutes, until it sets and secures the wires in place.
Insert a PNP Keying Transistor
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4
The PNP keying transistor functions to interrupt the power supply to the Q6 transistor. Trim the red and black wires on the PNP keying transistor to roughly 1 inch in length, using pliers. Insert the positive probe into the positive-marked hole above -- and midway between -- the two transistors on the circuit board. The positive hole will be marked with a white plus sign. Use the still-hot soldering iron to melt the end of the exposed probe at the back of the board, to secure the transistor in place. Leave the soldered wire to cool until it sets.
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5
Insert the negative probe of the transistor into the negative hole located adjacent to the positive hole, which will be marked with a white minus symbol. Use the hot soldering iron to secure the exposed end of the probe in place at the back of the board. Leave the circuit board for several minutes until the soldered wire has cooled and hardened.
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6
Place the circuit board back into the amp box so that the three main sections of the amp are aligned from left to right in this order: tubes and circuit board; transformer and power supply; and pi-greek and switches. Put the lid back onto the amp box, and screw the four screws back into place using the screwdriver.
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7
Plug the amplifier into the base radio unit. Set the radio to manual tuning. Turn the dial clockwise to the desired frequency, for example, 28 MHz.
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Tips & Warnings
Always turn any electrical equipment off at the power supply before attempting rewiring or disassembly.
References
Resources
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