I had the 110 voltage switch and the user ended up turning on 220v
Opening the amplifier you only notice that the 100uF/200 capacitor that feeds the 12ax7 tube is slightly bloated. I took advantage and tested all the power transistors of the audio output but I didn't find any shorted. You may have to change this capacitor (C411) and maybe the 12ax7 valve. The voltage of 10v that came out of the secondary transformer of the power supply feeds the filament of the valve, if it was connected to 220v this voltage was for 20v the same as the 200v which was close to 400v. I need to pass the budget on to the client. If I have to change this valve, where can I find this quality and affordable valve?

As of 2018 versions of the 12AX7/ECC83 are available from the following manufacturers:

In China: Shuguang and Quanzhen Electron Tube Technology (sold as TJ FullMusic[7])
In Russia: New Sensor, which produces tubes under the Sovtek, Electro-Harmonix, Svetlana, Tung-Sol, and Mullard brands
In Slovakia: JJ Electronic (annual production of approximately two million units)
https://en.wikipedia.org/wiki/12AX7#Manufacturers
https://www.amplifiedparts.com/tech-art ... made-tubes