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Old Cobra CB Tricks

Citizen's Band--commonly shortened to CB--radio originated in 1947, when the Federal Communications Commission, known as the FCC, decided on the need for a citizen's communication network. Dynascan, a leading manufacturer of CB radios, developed the Sidewinder CB in 1963, followed by the Cobra model. The name "Cobra" caught on and quickly became the corporate name. If you have an old Cobra CB radio and some basic electronics knowledge, you can improve its performance with a number of tricks.

Cobra 148 and F-GTL Tricks
- To receive extra channels on these old Cobra models, the MB8719 chip located behind the channel selector has to be altered by wiring switches on certain electronic contacts, or pins. According to the "Tips and Tricks" page on the DTB Radio website, "Wire a single-pole, single-throw switch from pin 10 to ground (SW-2 on chart), and another from pin 11 to pin 12."
Cobra 140/142 Tricks
- Receiving extra channels on Cobra 140/142 models requires a crystal change. Remove the 11.1125 MHz crystal and replace with an 11.3258 crystal. According to the "Tips and Tricks" page on the DTB Radio website, "Locate the MB8719 chip (usually right behind the channel selector). Isolate pin 10 from ground (Cut the trace). Wire a switch from pin 10 to ground (SW-2 on the chart), and another from pin 11 to pin 12."
Cobra 200 GTL-DX Tricks
- To improve noise cancelling on the microphone, change the R181 feedback resistor on the 4558 microphone preamp integrated circuit. According to the "Tips and Tricks" page on the DTB Radio website, the original resistor is 150 kHz, and changing it to a higher value, such as 470 kHz to 1 MHz, improves the microphone noise cancellation. A trick for increasing or decreasing the echo delay involves replacing the R550 with a 100K potentiometer.
Interference Tricks
- Interference can be a problem with old Cobra CBs, especially in mobile units. If interference constantly makes itself present, twist the power leads. According to "CB Radio Tips and Tricks," by Mark Truett, "Use twin lead type cable and run it all the way to the battery. Before hook-up, put one end in a vise and the other in a cordless drill and twist the wire up tight." Another interference cure is grounding the vehicle's body panels by connecting flexible grounding straps from the body to the frame, including the tailpipe. This helps eliminate interference from improper grounding.

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