Cobra 138 cb radio

It's the standard electric guitar plug (if you've ever fiddled around with those before) so all you need to do is figure out which wire is ground, etc, and go from there...look on cbtricks.com for a diagram....it would seem to me you'd want to stay away from those 5 wire mics (more wires to figure out)

It's a good radio for what it is, it's just it would get expensive if you want to mod it for channels (it only has 23) because it's a crystal radio (4+ crystals to replace, at about $15+ a piece...then finding someone who knows WHAT they're doing to do it...) If you want to go that way (40+ channels) get a Galaxy....

 

I know what he's talking about....and no it's not a 5 pin either....



At one time, some CB's used a mic jack that looked like a guitar jack, indeed. It took a plug like the above except it had a 3rd set of contacts.

The way it worked it worked was this: there's 3 connections...one, when grounded, activates the relay inside the radio. That puts the radio in transmit mode. The other 2 connections are for the mic element.

If you knew how to wire up a mic, you could buy you a 3 connector style mic jack from Radio shack and wire the switch in the mic as to provide a ground for the relay when pushed, and run the other 2 to the element.

The big question would be, if the radio is worth it to you. While those old cobras were good radios, and they'd give you channel 19, they're also limited to 23 channels, plus being that they're crystal controlled, the crystals might be a tad off frequency. Nevertheless still a good radio for tinkering with.

Here's a pic of my old Midland 13-871 which used the same style mic plug.

 

Inside this plug you will find only three points to attach a wire to sometimes there will actually be a screw on the terminals sometimes not.

The center pin will be easy to spot as it will be obvious it is in the center this pin will be the TIP of the connector and will always be the audio or pin

the center ring pin will be the next in line and will be the TRANSMIT pin this will be switched to ground when the mic is keyed.

the 3rd and largest ring is the ground and the shield will go on this and it will be the largest contact on the back side of the connector.

Hope this helps I could tell you how to connect the wires and what colors will most likely be the ones you want to connect to what pins if you need more help I will try to be helpfull I have worked on these radios since the day CB started so I have some knowledge of these old dogs.

 

I collect vintage CB radio's. I bought a Cobra 138 knowing it had 23 channels; but it was sideband. Well it had crappy sound reports from truck drivers. The meter did not light up either. I could not have an extra mic to try out. I liked the radio though. I bought another on Ebay. The meter light did not illuminate until I tapped it; but now it lights very bright and got good reports from truckers. This is a full size radio. I can talk to my wife on 16 lower sideband. Someday I will figure out getting a chrystal for channels 38.

 

Is it a pj-068 plug like this one?

If so, most of the microphones I use came stock with that plug..



Not sure if they are wired to work with your radio, but google aircraft microphone and search ebay images to find one cheap.

 

So apparently this exists.