I am just starting to restore my Princeton reverb blackface amp. First of all I have the following problems: The heating voltage of the rectifier tube is 4 volts, the heating voltage of the other tubes is about 5.7 volts. The anode voltage after the rectifier tube is about 440 volts without load, but as soon as I plug in the power tubes it drops to about 300 volts, which is much too low. So it looks as if the transformer (original 110 volts with 220 volts transformer before) does not provide enough power. How can this be? The Cs seem to be ok. Transformers don't usually get worse with time, do they? .... What ideas do you have?