Most solid state (ie not valve...or tube if you're from t'other side of the Atlantic) amplifiers run on low voltage, albeit derived from mains voltage. If you can find a mains amplifier that has an INTERNAL power requirement of 12V, it's a fairly simple procedure to disconnect the mains power supply and supply the thing with an external 12V supply. If you're not technically competant or confident, try asking at a local TV / Radio repair shop (or a competant electronics enthusiast).