what will be the polarity of the pin and the tube in a barrel connector?

Sep 21, 2024 Last reply: 1 year ago 5 Replies
M

I have a new-to-me device, a speakerphone from Radio Shack**, a Duophone



120,that didn't come with a power supply, and it works without one but is not very loud (and that was the reason I wanted a speakerphone).

It uses 9v dc.



I have two universal adapters (of different amperages). Both have a polarity switch with 2 sketches of a mini phone plug on them, one with the tip positive and one negative. But the device needs a tubular plug, a barrel connector (which both adapters have). If the switch is set to make the tip negative and the ring positive, what will be the polarity of the pin and the tube in the tubular plug.



What are the odds I'll burn it out if I connect it backwards?


**BTW, no one seems to sell new speakerphones anymore, unless they are part of a whole telephone. And even on ebay I didn't find one iirc. At a hamfest last week I found one for a dollar. When I got home, I found my own, that I had hunted for. It wasn't in the box of phone accessories. it was right on top of a stack of something right as I enter the spare bedroom. I walked by it at least once a month. LOL But the new one is a lot brighter. The colors of the old one are darker, probably from sunlight. Not that I care.

My current phone has a base and 3 cordless extensions and it does everything, but when I don't use the speakerphone, I can't hear the other party well, and when I do use it, the other party can't hear me well. To fix the latter problem, I red the manual and saw where the microphone was and I intended to clean the dirt out of the little hole in the case next to the microphone. But there was no hole. So I thought I'd drill one, but I want to know for sure where the mike is, and I don't want to drill through the case into the circuit. So I took all the screws out of the case, and it still won't come apart!! I looked under labels for more screws, but no. Why is there no hole? The Radio Shack speakerphones have 3 big slits for the mike!



To fix the foremer problem, I cleaned all the dirt out of the holes in the ear-part of the handset. they filled up agains quickly but even when empty, I can't hear some people, the soft talkerx. .


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B

The power supply amp rating should be as high as the phone requirement. should be.

In not too old of devices, there is usually a polarity symbol somewhere on the phone.

Try measuring the voltage at the connector on the phone. the polarity of the supply plug should match the polarity at the phone. If you see no voltage at the phone jack, it could be because it has a protective diode, which lessens the chance that the wrong polarity would fry things. You could open up the phone and try tracing the wires from the jack to a nearby capacitor, then check whether that wire is connected to the positive or negative terminal of the cap.

Significant.

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J

Maybe try one of these

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H

You can still buy the Manual on ebay - - and it has your picture in it ! :-)

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John T.

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M

Sorry it took so long to answer. There is a symbol, but I can't tell whether the + and - are pointing to the pin or barrel, even with a magnifying glass and a light. This is the one I bought for $2. Finally I found my old identical one and I think I can tell.

But then I connected the charger. I set the polarity to match the speakerphone, and even though it said 9v, I decided to start small, at

1.5V, and of course that had no effect. But then I forgot that I had started small, and I finally found speakerphones on ebay. I don't know why I didn't find any before. (I found a newer model RadioShack (and I bought one for $20. It's beautiful, like new) and ITT***. The ITT's are about $40 and don't seem to have a power input and they are Untested.) Still no ATT or Western Electric, and I don't know why) ***Both from the 1980's. The ones in the first paragraph are from the 1970's.

But before I disonnected the first one, I looked at the charger and it was 1.5v -- I never increased it. Stupid me -- so I increased it a step at a time, while listening to the weather, and by the time I got to

9v, I could barely hear anything. As if the polarity is reversed, but I'm sure it's not. I didn't damage it however and when the charger was unplugged, it worked the way it first did. Which was pretty well. Maybe there was soemthing wrong with the phone of the woman I talk with several times a week. I need more testing but I'd better post this now before I forget again.

Oh, it turns out all of the add-on speakerphones are half-duplex, though they didn't use that word in the 70's and early 80's. I found online a Uniden phone with speakerphone, much like mine, and it says it's like a walkie-talkie, and I suppose mine is too, though sometimes I think I hear my friend while I'm talking. OTOH, it would account for why I can never interrupt her when she is talking. I thought the manual for my model sayid nothing one way or the other, but I finally found in the opening list of features it says Duplex. I guess that means full-duplex. Darn, that means none of the separate speakerphones I have will be as good.

These are good ideas and I may have to do them. Maybe I was wrong about the symbol I thought I could read, because the 9 volts made things worse

Oooo. Aha, this is why I didn't reply when I first read this (and then I forgot). Wanted to see if I eventually burned it out or not.

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