Hi, I've got this problem on my Wangs Mini 5 amp. I've owned it since january and it just started doing this. It's got four tubes: 2 12ax7 preamp tubes (have swapped these out, no improvement) 12BH7 power tube 6Z4 rectifier tube I'm getting a red glow from underneath the socket for the 6Z4 rectifier tube, and a smell starts to come from there. I'm pretty sure that's where the problem is. Bad tube maybe? Or something worse? They've offered to refund me upon return, but I really love this amp and would like to save it if I can.