Quick DC polarity question

[johnm]

Sorry of this is in the wrong thread, but have a very quick question. At a friend's house (no multi-meter here etc etc). We have a DC mains lead which was cut off of an old wallplug PSU supply. This lead runs into a moulded DC plug. We want to use it with a Sonic Impact amp, but do not know he polarity of the wires!!! One wire is marked with a white dotted line. The other wire has a couple of grooves on the outside edge.

Anyone know which is which? Couldn't find this on Google but still trying.

Ta!

- JohnM

[Global]

Can you find a diode somewhere?

Run the PSU into a bulb through a diode. Try both diode polarities and see which way conducts (lights the bulb). Cathode is negative.

Mark