"Lukagain Cos ThistleBounce" wrote in message
...
On Sat, 16 Jan 2010 15:26:11 +1300, Lukagain Cos ThistleBounce
wrote:

Is the central pin positive or negative?
I've rediscovered this unit in the basement, but NOT the power supply,
and the case doesn't give an indication..

TIA ............... L
Oops ... a second, more careful look and I see its negative earth.

You can always use a device that will stop you blowing things up!
A simple diode. Connect it inline with the positive wire going to
your plug, in series with the wire so that the stripe is nearest the
plug. That will mean it will ONLY work if the device centre pin
is positive. You can also use a bridge rectifier to auto-select the
correct polarity. The should be built in to devices for a few pence
but manufacturers want to sell spares.