I have a problem with my Laney and want to see what you guys think. I have had amps serviced before but always thought I should learn and try to do it myself eventually. I think that time has come. I have no experience fixing tube amps but have been reading on it and feel confident attempting a diagnosis with a little help and from what I've read and seen changing tubes, which I think is what I need in this situation won't be too hard. The lead channel is working perfectly fine but the clean and Rhythm are not. Since the issue is focused on one channel only but everything else works perfectly fine it must be some tubes. How would you test what tubes need to be changed? Is there any visual cue I could take or do I have to open up the head and get my multimeter in there? Thanks a lot for any advice.