If the existing wall wart is dead, How will the OP will get the polarity right if he cannibalises a spare one. Will the leads be colour-coded, red and black, +ve & -ve, or if not, would it blow his radio if he got it wrong?
they are 99% inner +ve
Back when Radioshack still existed, they used to keep a mass of cables on the wall, with barrel fittings on the end. A customer could come in and fit their sample item, to the display thing, and discover what letter it was. There might have been fifteen barrel connectors or so at the time, and in some cases, two would fit, but only one of the fitments was actually "correct".
In any case, you can see there are as many variants as there are engineers with pencils.
Barrel connectors come permanently affixed to wall adapters. That's not a problem generally.
But the Radioshack general purpose adapters, the cable end had two equal holes on it. You could rotate an adapter and fit it to the end of the cable. This caused the polarity to be wrong. Other brands of adapters, the two hole thing, one hole was smaller than the other, and this served as a "key" to better control the resulting polarity.
The end result is, you test with a multimeter, that the thing you bought is actually correct for the appliance. Because there remains a small chance, it is not suited to the task.
The appliance casing should have symbols stamped in it (black symbols on a black background), as to what kind of adapter is required.
# Polarity
It often states on the appliance,
The polarity, voltage, and either current or wattage, will be printed somewhere on the wall wart.
Open the radio or the dead wall wart and work it out that way.
A few are but it isnt that common.
Not usually.
It often states on the wall wart.
But no standard that defines which connector is +ve and which is -ve (assuming DC output).
Some are marked and the manual for the radio might show the polarity of the connector. Don't assume that they are all the same.
Thank you!
Thanks again to all who responded. The wall wart and the appliance are both marked with power requirement/supply details, and the polarity. In this case positive is inner. I shall seek out a suitable wall wart on line.
I'd have offered you one from my vast collection of wall warts built up since my Commodore Scientific Rechargeable Calculator died in 1981. I never threw out a working wall wart. I put many into the electronics recycling skip at my local waste site when I had a huge clean up when my "office" had new windows fitted. I stopped counting at 100. But don't feel sad for me, there's still plenty remaining but mostly switching PSUs now, the transformer based ones had to go!
If the connectors don't match, the obvious thing to do is to chop the lead off the faulty PSU, and graft it onto the lead of the new one.
If there are marking, they might look like this.
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