How to identify the pins on a DC input socket (jack)?

I have a couple of dc input jacks that i have de-soldered from old electronics, and I now have the need for such a jack as i am making a mini guitar amplifier.

However, I don't know what the connector lugs are each of them, and am not entirely sure whether they are the type with are usually closed (have a switch in them) and only break the circuit to use external power source when a jock is plugged in. I suspect they aren't that sort, because I think they would need more connections than these have.

One has 3 solder lugs, the other only has 2.

Here are some pictures to help make it clearer (sorry for bad photos, with the amount of great light tent instructables on here, you'd have thought i'd have made myself a better macro setup than this by now)

Picture of How to identify the pins on a DC input socket (jack)?
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Take a look at the pictures in the data sheet linked below.  This part looks similar to yours, the one in your first pic, with three terminals

That page is from Digikey's online catalog.  If you like, you can go in through the front door, and search for a closer match:

It's a barrel-type, through-hole, power connector, that does or does not contain an internal switch.

A few words about the internal switch. The jacks containing a switch have three terminals.  The jacks without a switch just have two terminals. 

The internal switch is normally closed when there is no power plug inserted, and open when a plug is inserted.  I think the reason it is there is so that if you have some, thing, e.g. a toy, that runs on batteries or a DC adapter, it will switch in the batteries when a plug is not inserted, and disconnect the batteries when a plug is inserted.

Also you can puzzle all this out using an ohmmeter, and doing that is somewhat easier if you have both the plug and the jack.

ARJOON6 years ago
it depends on the wallwart u are us3ing usually it is the center pin in this3 socket the positive.
mdog93 (author)  ARJOON6 years ago
So is it positive, negative and ground? If so which is ground.
ARJOON mdog936 years ago
cons3ider the negative to be ground
the pin in the back of the s3ocket is3 pos3itive. the res3t is3 ground
mdog93 (author)  ARJOON6 years ago
so i would attach two of them together and attach those to the negative?
ARJOON mdog936 years ago
if you w9ant. if you are using current more than 1 amp then yes
mdog93 (author)  ARJOON6 years ago
erm, i don't know what the amperage will be. So just to clarify this wouldn't be suitable if i need a jack with a built in break switch would it?