I just received my SL5 combo. It sounds pretty good but I have a ton of tubes to try out in it. I did find one issue...I went to switch it to 1w instead of 5w and it sounded like I expected, but when I went to switch it back to 5w it hissed and gurgled for several seconds before it finally stopped and worked normally. I tried it a few more times and it did it again once when I didn't FULLY force the switch into the 5w position. Is it a dirty/sticking switch? I only got it to do it twice and it hasn't done it again since, so maybe it is gone? Side note, any recommendations on tubes? I have a couple of old Svetlana EL34s.