I have an AC 15 hand wired Vox. Yesterday at practice, it couldn't get louder than the drums. I checked it with and without my pedal board, and with other guitars. It's definitely the amp. I was plugged into my usual wall outlet. I don't know much about tubes. All five were glowing, three large and two small. I couldn't really tell if the tone was different but it sounded pretty much the same, just quieter. Any thoughts on what it could be?