a15mk1 power on

Hi there,
recently I noticed that my A15Mk1 takes up to 5 or 6 seconds to light up the power supply switch...
I mean I turn the switch on and after 5 or 6 seconds the light inside the switch turns on and the amp becomes fully funcional. I did not noticed it in the first days of use. Is it normal? what can cause my problem?
Is seems like a capacitor has to charge before the light on the switch turns on...
Any help is really apreciated.
Krusty