Several years ago I gave my son one of my blueprint teles, and my Blues Junior along with it. He didn't play it much at first, but he's been learning to play the last couple years, mostly on acoustic but he's used the rig occasionally. The amp has developed a problem: when you turn it on it makes a loud, steady shrieking sound, no matter what you do with the volume. The sound continues until you turn the amp off, and it seems to be affected neither by any of the controls, nor by plugging in or unplugging the guitar. No sound comes through at all from the guitar. The guitar works OK on the dinky little Johnson practice amp I gave him at first, so I don't think it's the problem. My son is coming down for Thanksgiving. I asked him to bring the Blues Junior, and let me see if I can get it back in operation. I told him he could take one of my Peaveys back with him while I have his amp. I'll take it to a tech if I have to--probably have to travel for that--but are there things I can do myself by way of checking, or does someone who's experienced this have suggestions for which part might need changed? I have a multimeter, but I'll need some, er, coaching on how to use it. Thanks in advance.