I recently bought an Art Tube mic preamp. We were doing a recording session and didn't have a properly rated power supply for it, so I used it anyway (foolish I know!) and after 12 hours of use I burned something out. The preamp wont power up at all. The MP is 9v AC and is rated at 700 mA, and i used a 9V AC rated at 780 mA. If anyone has any suggestions on which compoments I might take my voltmeter to first it'd be appreciated. p.s. is the tube still okay?