I bouught one from ebay for 7.99 GBP as the original was too old and stoped working. Not sure where you are, but i'm in germany and just used a uk/eu adapter and it works great. The ebay seller's link is below. If you want to get it yourself, the specifications written on my plug are as follows:

Input 100-240v
0.5A maximum, (i.e 500mA) 50-60 Hz
+12 v
Output power 6W max

If you've got a PSU with multiple adapters then maybe you'll have the right one already, but you should note that the 707 has a slightly unusual shape to the PSU tip so it's important to buy one the right size as well as voltage, polarity and Amps.

http://stores.ebay.co.uk/effects-pedal-power-supplies

--- In tr-707@yahoogroups.com , "gafbf" <gafbf@...> wrote:
>
> Hello people.
>
> I am trying to find a good power supply for my TR-707.
> Somebody knows the exactly voltage do I need
>
> In the gear is just written 12v DC, I've try one power supply with 100 ampere, and it seem that it is not enough.
>
> Cheers!
>