Been about 4 years since I've changed my tubes. Amp sounds fine in modern on channels 2 and 3 and pushed on channel 1. Every other mode gets its volume cut dramatically and sounds like crap. I know this is supposed to happen to a certain extent (the volume cut, not the crappy sound), but I have no way to play clean then dirty at all. No matter what volume I have channel 1 at, It cant keep up with channel 3 at all. I know its probably tubes, but which ones? All the power tubes still look good. All glowing the same and everything. I've read somewhere that you should change power tubes more often than the pre-amp tubes. Does this hold any water? And yes, I know power tubes = volume.
Bad tubes? (Pre or Power)
- Thread starter mexirican
- Start date
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elvis
Well-known member
If any of the modes sound good it is probably not power tubes or the PI tube.
Yes, under ideal circumstances (no premature failures) power tubes won't last as long as preamp tubes. But tubes today are made very cheaply and often fail prematurely. I have had a few preamp tubes die and no power tube fails.
Your best bet is to swap a known good preamp tube into one slot at a time and check until you find a change in operation. You may be done, or there may be more bad tubes.
Enjoy!
Yes, under ideal circumstances (no premature failures) power tubes won't last as long as preamp tubes. But tubes today are made very cheaply and often fail prematurely. I have had a few preamp tubes die and no power tube fails.
Your best bet is to swap a known good preamp tube into one slot at a time and check until you find a change in operation. You may be done, or there may be more bad tubes.
Enjoy!
I would agree with Elvis.
There is generally a bias voltage shift on the preamp tubes depending on what channel you are in. The highest gain channel will generally use the higher voltage on the preamp tubes to enhance the saturation and gain structure as well as boost the higher frequencies. There is a mention of what tube positions have cathode follower circuits in the FAQ thread. The cathode follower circuits tend to be hard on the preamp tubes so those would be first to change (use only Mesa JJ branded tubes or Chinese for the cathode follower positions, Russian tubes will fail prematurely in those positions: Mullard, EH, TS, Sovtek, Russian Groove Tubes, etc .) It could not hurt to replace all preamp tubes either, but you can do the sub with a good tube. Dual and Tripple Rec have cathode followers in V3 and V4. I believe that V3 is the tone stack and V4 is the attenuator for the effects loop. You can get away with most tubes in V1, V2 as well as the PI tube. I have also read some posts on volume drop which may have been in relation to preamp tube in the V3 position. Not exactly sure when the hard bypass for the FX loop came into effect, if you have it on your amp, try the hard bypass and adjust the channel master volumes accordingly. At least you can rule out V4 that way if there is no change in character.
If changing V3 or V4 has no effect, the next culprit would be the Rectifier tubes. Sometimes they may cause some issues as well. I have yet to encounter a bad Rectifier tube in my Roadster, but I have had many issues with the single Rectifier in my Mark V even when it is bypassed by the diodes. I believe the Rectifier amps disconnect the Rectifier tube entirely when switched to silicon diode (case with the V, it runs in parallel to the diodes) so that may not be an issue. If you decide to change the power tubes you should also replace the rectifier tubes at the same time.
There is generally a bias voltage shift on the preamp tubes depending on what channel you are in. The highest gain channel will generally use the higher voltage on the preamp tubes to enhance the saturation and gain structure as well as boost the higher frequencies. There is a mention of what tube positions have cathode follower circuits in the FAQ thread. The cathode follower circuits tend to be hard on the preamp tubes so those would be first to change (use only Mesa JJ branded tubes or Chinese for the cathode follower positions, Russian tubes will fail prematurely in those positions: Mullard, EH, TS, Sovtek, Russian Groove Tubes, etc .) It could not hurt to replace all preamp tubes either, but you can do the sub with a good tube. Dual and Tripple Rec have cathode followers in V3 and V4. I believe that V3 is the tone stack and V4 is the attenuator for the effects loop. You can get away with most tubes in V1, V2 as well as the PI tube. I have also read some posts on volume drop which may have been in relation to preamp tube in the V3 position. Not exactly sure when the hard bypass for the FX loop came into effect, if you have it on your amp, try the hard bypass and adjust the channel master volumes accordingly. At least you can rule out V4 that way if there is no change in character.
If changing V3 or V4 has no effect, the next culprit would be the Rectifier tubes. Sometimes they may cause some issues as well. I have yet to encounter a bad Rectifier tube in my Roadster, but I have had many issues with the single Rectifier in my Mark V even when it is bypassed by the diodes. I believe the Rectifier amps disconnect the Rectifier tube entirely when switched to silicon diode (case with the V, it runs in parallel to the diodes) so that may not be an issue. If you decide to change the power tubes you should also replace the rectifier tubes at the same time.
no need to worry, I type a lot anyways. Perhaps TMI?
More than likely it is a preamp tube. If you have a good one, swap V1, Nothing changes, move the good one to V2 and return the original. Repeat with the other tubes until the issue goes away. My hunch is on one of the cathode follower tubes (V3 or V4).
However, if you have noticed a dramatic tone change, no bass, sharp treble, raspy tone or distortion in clean it may be a power tube. You comments seem to indicate a preamp tube. The question is,, how often to you play and how long. Some power tubes will last quite a while if the use is minimal over that period. I had a set of Mesa STR420 in my Mark IV for 14 years as well as the original preamp tubes. I did not play much during that 14 year period (hence the reason for the lifespan). I replaced all tubes 2 years ago and it never sounded better, not that it seemed to need new tubes. In most cases the change is gradual. However if you play many hours a day the change will not be gradual. If you start blowing fuses, time to change all power tubes.
Look in the Mesa Manual for your amp, (or any of the manuals, if you do not have one, you can get it from Mesa's web site). Mesa usually has an article on preamp tube issues, and power tube issues. Too bad they do not mention side effects of Rectifier tubes as that can be quite different since it is not an audio tube.
However, if you have noticed a dramatic tone change, no bass, sharp treble, raspy tone or distortion in clean it may be a power tube. You comments seem to indicate a preamp tube. The question is,, how often to you play and how long. Some power tubes will last quite a while if the use is minimal over that period. I had a set of Mesa STR420 in my Mark IV for 14 years as well as the original preamp tubes. I did not play much during that 14 year period (hence the reason for the lifespan). I replaced all tubes 2 years ago and it never sounded better, not that it seemed to need new tubes. In most cases the change is gradual. However if you play many hours a day the change will not be gradual. If you start blowing fuses, time to change all power tubes.
Look in the Mesa Manual for your amp, (or any of the manuals, if you do not have one, you can get it from Mesa's web site). Mesa usually has an article on preamp tube issues, and power tube issues. Too bad they do not mention side effects of Rectifier tubes as that can be quite different since it is not an audio tube.
I practice with my band 3 times a week for about 2 hours each time. Amp is pretty cranked while we are playing too. Channel volume is always @ 50% and my output is between 20-25%. I have some old pre-amp tubes that I can transfer around. Hopefully that will be the problem. 5 new pre-amp tubes are only about $80. I have had power tubes blow on me before and take the fuse with it. Haven't had that happen in a few years so I'm confident they are fine. Going to change them at the beginning of the year anyways. Looking to try something different so I'm going to try the KT88 sextet from Eurotubes. 
Any update regarding this? I was just about to post a very similar topic, when I saw this. My Roadster seems to act the same - very low output on the clean channel, regardless of mode it's in. I normally use the "fat" mode, have channel one master nearly dimed, and the gain beyond 12:00 just to get near the volume of the other three channels. I have the overall master output fairly low for in- house playing. I have recently changed the power tubes (all) and both rectifier tubes, and rolled in a Tung Sol pre in V1. This was all done two months ago.
This morning, I replaced my pre amp tubes. There is an improvement, but the overall volume is not quite comparing channel one with the rest. I assume this to be normal due to the higher gain structure of the subsequent channels and have adjusted master controls on those channels to balance them.
I've a small collection of pres from a set I ordered from Eurotubes. They are JJ high gain types. I've also ordered JJ power tubes from Tube Depot in the past. There a couple music stores about an hour away from me that handle Mesa original tubes. The next replacement cycle will most likely be from them.
I would not rule out the PI tube. I recently have been experimenting with change in preamp tubes in my Roadster and noticed similar results with the CH1 and CH2. I have rolled the stock tubes and found one that sings in the PI (notable difference in Ch1 and CH2, seemed a bit more present in respect to CH3 or CH4.) Keep in mind, this amp is a Class A/B, if the PI tube triodes are not close in rating to each other (matched or balanced) it may be possible that if one half of the tube is weak, the amp will sound as if you are pushing half the power with a clean signal, with higher gain channels it will actually bring up the weak side of the PI tube and not be noticeable.
This thread made me want to get more tubes. This time I decided not to buy other brands but Mesa. Full set for the Roadster so when I need it I will have it. I did have a surplus of Mesa tubes, not any more, they are all in use, bad one's were removed (had a few noisy preamp tubes, not just Mesa either. Figured I would give the SPAX7 a go.
