Cobra CB models 25 and 29 (all versions)
DESCRIPTION: Adding talkback
ACTION: Talkback can be easily added to these radios by installing a resistor from the
sleeve of the external speaker connector to ground. See picture of the location.
Adding a resistor will give a fixed audio level on the talkback. Try starting with a 100 ohm resistor, and adjust as needed for the desired volume level.
If an adjustable talkback level is desired, a potentiometer can be used in place of the resistor. A 200 ohm potentiometer is recommended.