Cobra 25, 29 Uniden PC 66, 68, 78 Talkback Mod

This is a easy $1 mod to add talkback to your CB Radio.
This will work for the following radios with no problems.

Cobra 25
Cobra29
Uniden 66
Uniden 68
Uniden 76
Uniden 78
and many more.

All you need is a simple resistor added to the bottom of the board, near the Ext and Pa speaker jacks.

Find the 2 solder points, closest to the rear of the radio, directly above the EXT and Pa jacks.
These are going to be the Negative or Ground side for the audio.

Solder a 1/4 or 1/2 watt resistor between these two solder points. Make sure that the resistor itself does not short out anything on the board or touch anything else. You can wrap it in tape, heat shrink or just keep it lifted slightly above the board.




Use a 100-500 ohm resistor.
The Lower the resistance is, the Louder it will be.
A 100 ohm will be Louder than a 470 ohm.
I like to use a 220 for most mics, or a 470 for good power mics.
You can also wire up a 1K variable pot to adjust the volume level.
You can also use a switch to turn it on/off, just wire it in series.
Ive used the Norm/Ch9/Ch19 switch as a Off/Low/Hi with 2 resistors, to make it adjustable for different mics or volume levels.


Thats it! Just 2 solder points for basic talkback.

CB Mic Connector Problem

If you have ever had a CB mic that randomly cuts out on the Receive, Transmit or Audio, even when you have checked the wiring in the plug and it seems fine, then this is the EASY fix for most radios.

Most radios, including Cobra, Uniden, Galaxy and more use a connector that can fail easily, but its a simple 30 second FREE fix.
This is only for 4 pin microphone connectors, as the 5 and 6 pin are built different.

If you look closely at the male pins on the radio's connector, you will notice that they are split down the center. I have found over the years that these pins tend to get pinched together and flattened, when they should be slightly spaced apart, to create a good electrical connection.


Simply take a small flat head screwdriver and push it into the slots on the pins and spread them SLIGHTLY apart. Spread them less than 1mm. If you spread them too much, you can bend they way out of place and they may break when trying to bend it back.
This allows the MALE pins to fit better into the FEMALE holes in the mic's plug.

this should solve most problems, as long as the wires are soldered properly.
I have done this in over 50 radios over the years after other people have tried to re-wire mic plugs and swap out mics endlessly, when it was just a simple bad connection thats easily overlooked.

Cobra 148 GTL Audio and Power Mods.

A simple way to really increase the audio of a Cobra 148 GTL CB radio is to find R126 and jumper it. It is a 10K ohm resistor about 1" to the LEFT of the MIC jack.
Do NOT remove the TR25 Mod Limiter on this radio, as it will sound like crap later.

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To add extra channels install 2 switches in the radio, or use the HI/LOW and BRT/DIM switches on the front.
My friend wanted 2 new switches on the rear, so thats what I did with this radio.

You will need 2 SPST switches.

Find the PLL IC and find pins 10, 11 and 12 and the large Ground trace near pin 10.

Wire Switch 1 to Pin 10 (pin goes to nothing) and also to GND pad.
Wire Switch 2 to pin 11 and pin 12.
Be very careful to not use too much heat on the IC pins, and they are fragile and you can damage the PLL chip. Use a 30watt max solder pencil.

RX Recieve boost on Cobra 29 and Uniden PC 78

Here is a very simple was to use 1 or 2 components to add super recieve boost to a Cobra 29 or Uniden PC78 CB radio.

Parts + tools required:
CB radio (duh)
Soldering pencil 15-40w. Do NOT use a large gun.
Small solder like .032" 60/40 mix or similar mix.
22-24guage wire
220k to 470k ohm 1/4 or 1/2watt resistor.
Simple SPST switch or existing switch on radio.

Disconect the power cord from the radio. Dont do any work with it plugged in, just in case.

1st find pin 14 on the PLL of the radio. Do this with the radio upside down, front facing you.
you will see that Pin 14 is a blank pin with no traces, or it may have a small capacitor on it going to the large ground trace.
Solder a wire to that, being very carefully not to use too much heat or leave it on too long, as the PLL chip is very fragile.

Attach this wire to your switch with about 4-8" of wire, depending where your switch is located. If using an existing switch read below. I prefer to use the pointless CH9 switch.

On the other side of the switch connect your resistor. Be sure to trim the resistor so it doesnt have a long leg to where it may touch anything else.
On the other side of the resistor, add about 6-8" of wire.

Now find Resistor R11. You will need to tap the wire onto this resistor on the end of the resistor closest to the BACK of the radio. If you test it, you should get about + 0.8volts from here. This is going to supply the power for you receive boost.

Thats it! 2 wires, a switch and a resistor.
The reason you need a switch is cause this is going to be VERY sensitive and you should only use it when you need it, cause strong signals may peg your meter.
I got results of a signal of 2db with the boost off. I flipped it on and it jumped to 10+db.
This doesnt just increase the meter reading. It boosts up the actual receive and makes it so much louder and clearer.

I recomend using the 470k ohm resistor as the 220k may be too high, and the 470k is plenty for any of my customer's needs.

This should work on all the Cobra 29 models.
Cobra 29 WX
Cobra 29 LTD
Cobra 29 Classic
Cobra 29 ST
or any other variation, Except the older D858 PLL chip.
It also works for the Uniden PC 78 models or any variation.