Midland 13-857 Talkback Mod?

[Midlander853]

Hi everyone,

I have a good-looking Midland 13-857 that was quite the eBay steal. I'm wondering if there is an easy mod I could do that would add talkback to it. Would this radio work with the resistor mod that most Cobras use?

This link outlines the mod if you're not too familiar with it: https://cbradiomagazine.com/adding-talkback-to-your-radio-and-easy-modification-for-beginners/. Oddly enough this radio does have both external and PA jacks.

Thanks!

 

[nomadradio]

Pretty sure it should work on that one.

73

 

[Midlander853]

Pretty sure it should work on that one.

73

Awesome. I'll give it a shot.

One more thing, it has 3.5mm jacks that look like this:



Is the ground terminal the one closest to the front of the jack? For reference here is the section of the schematic I'm worried about:

 

[nomadradio]

Is the ground terminal the one closest to the front of the jack?

Yep.

73

 

[Midlander853]

And that's where I'd bridge the resistor as well, is between the two ground pins?

 

[brandon7861]

Yes. Connect the shield pin of both jacks together via the resistor.

Normally, pressing the PTT switch opens the ground to the speaker so the speaker shuts off during TX, but the PA jack shield is AC coupled to ground all the time via C98, so connecting the two shield pins via that resistor completes the speaker circuit when the PTT is pressed.

 

[Midlander853]

Normally, pressing the PTT switch opens the ground to the speaker so the speaker shuts off during TX, but the PA jack shield is AC coupled to ground all the time via C98, so connecting the two shield pins via that resistor completes the speaker circuit when the PTT is pressed.

That makes so much sense!

In the circuit though C98 is connected to 13.94V when the radio is in PA mode. So technically the ext. CB/PA shield isn't grounded?

I feel like I'm not looking at this right

 

[brandon7861]

Either way, ground or positive rail, same effect. This is because the audio is from the center tap of the transformer and the positive supply is at AC ground due to the filtering caps, so whether we send it to actual ground or the positive rail, no difference. It is a convenient and easy to find location. It may not be DC ground, but it is to AC audio.

 

[Midlander853]

I'm back...

Well, it actually works! I have to put the radio in Ext. CB mode but it works great!