I have a Valvetech Hayseed 30 with the EF86 channel. It has developed a hiss that gets louder as you increase the volume. I have retubed it completely with new tubes, Power, preamp and rectifier tubes. Anyway, it was better but not as quiet as it was, so I email Rob at Valvetech to see if I could get it in to him to check it out. He sends me back a reply stating that a hiss is normally a tube issue. This sounds reasonable to me so now I get to try to find a bad tube. So I am looking for a good, fast way to find the culprit. I am sure many of you have done this same thing, I am looking for any hints, tips or tricks to make this as painless as I can. I have a few known good 12ax7's and a good EF86. I am not sure I have 4 EL84's though. Thanks for the help.