Hey Sly, how you been, before we get to deep into this, is this amp a Vibrolux or a Vibrolux Reverb? Is it an older Silverface or a Re-issue? To answer some of your questions, yes an amp can operate with a blown power tube but not very well, a big loss of volume and a weird sounding distortion is a dead give away, some amps will not survive too long with a blown power tube, part of what the power tubes do is match the impedance of the output transformer and you can see why one tube being blown in a push-pull circuit would cause a problem, Fenders are fairly rugged in this area but this isn't something to be left unattended, tubes are cheaper than output transformers, Cranking the amp above 5 and getting some distortion is a good thing, you are pushing the power tubes into clipping and thats normal for a non-master volume amp, and by the way it's a two channel amp, should be 2 jacks for the normal channel and 2 for the vibrato channel, the Tubes in that amp should be (if it's non-reverb) 3-12ax7, 1-12AT7, 1-GZ34, and 2-6L6, as to what color the tubes appear, if the 6L6's are glowing bright red/orange their is a problem with the bias , probably just needs adjusted and the sooner the better, if they are glowing blue it's just some off gassing from the plates, no problem and very normal, well Sly keep me informed, if I was an E/Eng student I think I'd better pretty excited because old Fender amps like that are great for learning about tubes, and if you got the bug for doing some mods to it their are a ton of things you can do very cheap that are just a blast, I have a 67 Bassman that is an source never ending experimentation, quite fun for those so inclined.......

[Edited by pstring on 10-04-2003 at 03:42 PM]