feylya Posted February 17, 2005 Report Share Posted February 17, 2005 A guy that I do some guitar work for has been complaining that he hasn't been able to get decent tone out of his Marshall Valvestate 8080 any more. He said he bought it second hand about 4 years ago and has never replaced the preamp tube. Would I be right in thinking that it's toasted? If I'm right, is it just a staight pull out the old one, push in the new one kinda job? Quote Link to comment Share on other sites More sharing options...
Gorecki Posted February 17, 2005 Report Share Posted February 17, 2005 (edited) Four year old tubes if used regularly should be shot by now. Tubes either just stop working or progressively sound worse and worse. It would be wise to replace all tubes at the same time using matched sets. I don't know what's in this amp. Yes, it can be as simple as pop it out, pop new one in (while powered off and unplugged). I use Groove Tubes exclusively because of the tone I get with them and they also seem to last for a very long time. Edited February 17, 2005 by Gorecki Quote Link to comment Share on other sites More sharing options...
feylya Posted February 17, 2005 Author Report Share Posted February 17, 2005 Yeah, the sound has been getting worse. There's only 1 12ax7 in it so matched sets aren't required. Quote Link to comment Share on other sites More sharing options...
Gorecki Posted February 17, 2005 Report Share Posted February 17, 2005 Okay..cool, ya pop that puppy out and replace it, pretty hard to match one tube. Quote Link to comment Share on other sites More sharing options...
ripsrv Posted February 18, 2005 Report Share Posted February 18, 2005 might be a good idea to get that amp re biased. if u dont us the exact same tubes dont you have to any way? i could be wrong. but yeah that is the tubes. Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 18, 2005 Report Share Posted February 18, 2005 (edited) You shouldn't ever have to bias preamp tubes - just swap it out with whatever cheap 12AX7 you can find. After all, it's a ValveState, so there's very little point in installing a NOS Mullard or Telefunken, or those expensive Chinese tubes Pittman's pushing - those $8.00 JJ/Sovteks will work fine for this. Edited February 18, 2005 by lovekraft Quote Link to comment Share on other sites More sharing options...
GuitarMaestro Posted February 18, 2005 Report Share Posted February 18, 2005 Just want to add that preamp tubes can easily work for that amount of time. Often if people claim the sound of their amp gets worse and worse it's just that they become more sensible to it's weak spots. Considering this is a crappy valvestate I would not be surprised....In this case I would just change the tube and try if it makes a difference. But for amps with many tubes it's often a better idea to play the same amp in a store or somewhere and check if it is really the tubes or your ear.... Quote Link to comment Share on other sites More sharing options...
feylya Posted February 18, 2005 Author Report Share Posted February 18, 2005 Well, the tube he's getting (if he actually listens to me) is €12 so it's not too bad. Can you rebias one tube? My tube amp knowledge is somewhat limited unfortunately. Quote Link to comment Share on other sites More sharing options...
westhemann Posted February 18, 2005 Report Share Posted February 18, 2005 Well, the tube he's getting (if he actually listens to me) is €12 so it's not too bad. Can you rebias one tube? My tube amp knowledge is somewhat limited unfortunately. like lovekraft said,you don't bias or match preamp tubes....only power amp tubes. the mode 4 is a valvestate amp,basically.i have already replaced the tube once.just pull out the old one,push in the new one(line it up right) Quote Link to comment Share on other sites More sharing options...
feylya Posted February 18, 2005 Author Report Share Posted February 18, 2005 OK cool. I think he's gonna be doing it himself (he should be able to, he has a masters in Engineering) Quote Link to comment Share on other sites More sharing options...
thedoctor Posted February 18, 2005 Report Share Posted February 18, 2005 12AX7s are a great little tube but I get one out of, say, twelve that sound like CRAP! Test fine but sound horrid. That is one tube to keep a couple of known-good spares around for. Some of them are just plain noisy but pass a leakage test. What's up with THAT? Quote Link to comment Share on other sites More sharing options...
Gorecki Posted February 18, 2005 Report Share Posted February 18, 2005 Manufacturing QA will always have 'duds' get through, the cheaper the tubes, the more likely the inconsistancies. If anyone says 'One AX7 sounds like any other AX7', I'll come down and kick ya in the head myself! Quote Link to comment Share on other sites More sharing options...
lovekraft Posted February 18, 2005 Report Share Posted February 18, 2005 Point well made - no two 12AX7s have ever sounded exactly alike. The fact that the original 7025s (high gain/low noise) were simply the best of the production 12AX7s selected after manufacturing should prove that. I still maintain that any inherent superiority in tone is completely wasted in a solid state amplifier like the ValveState. Quote Link to comment Share on other sites More sharing options...
westhemann Posted February 18, 2005 Report Share Posted February 18, 2005 I still maintain that any inherent superiority in tone is completely wasted in a solid state amplifier like the ValveState. could be...but i ordered several different 12ax7s and tried quite a few of them before i was happy with one. the difference was very subtle,but some were a bit harsher Quote Link to comment Share on other sites More sharing options...
syxxstring Posted February 19, 2005 Report Share Posted February 19, 2005 I just got Aspen Pittman's The Tube Amp book. There is a whole section on the different 12ax7s and their uses/differences. One of my next purchases will be a huge variety of these to play with in my amps. And my wife was worried here getting me the book would just enable me.... Quote Link to comment Share on other sites More sharing options...
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