a15mk2 problems

Hi jelle and welcome to the forum. Did you measure successfully the secondary AC voltages at the power transformer set out in chapter 2.4.1? And with "as soon i put my amp on" you mean when flipping the standby switch with power switsch on OR flipping the power switch with standby off?

Well, if you're not sure you should repeat the masurements set out at the end of chapter 2.4.1 and chapter 2.4.2 (you have to desolder some wires and remove the tubes to repeat these measurements). This will tell you, if the transformer is OK (chapter 2.4.1) and if the power supply board parts and wiring is OK (chapter 2.4.2).