Ok. Just bought a DT25 head and cab. Brought it home, hooked it up to my 500x via xlr cable. Every thing seems to be working correctly. Sounds great etc. but... The red power light doesn't light up. Never did! I would think that it's just the bulb. How easy is this to replace? Is this done by unscrewing the knurled light cover from the front, or do you have to go in from the back of the amp. I can't take it back to the shop as I live miles away and was only able to get there due to a friend giving me a lift. Thanks for any information.