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Over the holidays I acquired my first tube amplifier, a VOX VT20X. I'm not really sure whats required to keep a tube amp sounding its best for as long as possible or if they even require special treatment. what do you suggest I do for keeping it in optimal condition? Are there any circumstances or situations I should be wary of?

Matthew Mccall
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  • In the immortal words, "RTFM" - and then do what it says! From a quick look at the VT20X manual, it seems a fairly "user friendly" design. High power tube amps designed 50 or 60 years ago were much less "idiot proof" than modern ones. –  Dec 31 '16 at 22:04
  • i did read the manual. it seemed 'too' straight forward which is why i got concerned. – Matthew Mccall Jan 01 '17 at 05:27

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There's no special treatment, just avoid mechanical shock (tubes have parts that can move under shock, and they're obviously in a glass envelope), and moisture (including beer ...), the latter of course being true for any electronic equipment. And, as a rule of thumb, never leave your tube amp anywhere where you wouldn't want to sleep, e.g., in a trunk of a car parked in the cold etc. Tubes are also especially vulnerable when they're hot, so don't move your amp too much before it has had a chance to cool down.

But in general, tube amps are more resilient than many people think. Don't worry too much, just use common sense and the above tips.

There's no need to change the tubes as long as you don't notice any strange noises, and as long as you're happy with how it sounds. You would normally change the power amp tubes much more often than the preamp tubes, because they get to do all the work. Don't forget to have your amp re-biased after changing the power amp tubes. But it may take years before you might need to change them for the first time. On average, the more often you use the amp, and the louder you play, the sooner you'll need to replace the power amp tubes.

EDIT: re-reading the question I noticed that the amp model you got is a Vox VT20X, which is actually not a conventional tube amp, but a modeling amp with only one single 12AX7 preamp tube, and no power amp tubes. Everything mentioned above remains valid, but you won't need to worry about biasing and everything else related to power amp tubes. Furthermore, chances are that throughout the whole lifetime of the amp you won't need to worry about replacing that one preamp tube.

Matt L.
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  • Agreed that tubes amps are resilient and as such my experience is that leaving one in a car in overnight freezing temps is fine as long as you let it come up to room temp before turning it on again. Also tubes definitely degrade over time (in six months or less with daily play) so replacement is definitely an ongoing and regular consideration. Also power amp tubes last *longer* not shorter than preamp tubes. If the amp has a bias control it should normally only be adjusted by a tech since you have to make dangerous voltages exposed to access it. – Todd Wilcox Jan 01 '17 at 07:11
  • @ToddWilcox: Of course you can leave your amp in the car overnight, but it's better if you can avoid it. Replacing tubes is an important consideration, otherwise I wouldn't have mentioned it in my answer, but for most amateurs who don't use the amp many hours each week, it can take several years before tube replacement becomes necessary. I know that from a good friend of mine who earns his living with tube amp maintenance. – Matt L. Jan 01 '17 at 07:57
  • @ToddWilcox: Finally, you're wrong about the longevity of tubes: it is definitely the *power* amp tubes that must be replaced much more often than the preamp tubes. Ask any amp tech, or read [this](http://blog.hughes-and-kettner.com/does-it-pay-to-regularly-swap-tubes/) "Preamp tubes are more compact and don’t have to work as hard, so they tend to last even longer, or seemingly forever ...". This fact is also mentioned in [this answer on this SE site](http://music.stackexchange.com/a/1073/9724). – Matt L. Jan 01 '17 at 07:58
  • I've run with the same power tubes for years without degradation in sound while the preamp tubes definitely stop sounding the same much more quickly so I don't know what to say. Perhaps it's a matter of personal preference. I know if I keep gigging, after maybe six months the same settings don't sound right. Then I replace the preamp tubes and everything sounds right again. Replacing the power tubes with the exact same kind is virtually undetectable to my ears, even after years. – Todd Wilcox Jan 01 '17 at 08:12
  • Both of your references discuss the operational lifetimes of tubes, I.e. how long they last before *failure*. But tubes degrade in sound quality long before they approach possible outright failure, in a way similar to guitar strings. The quality of sound imparted by the first gain stage is amplified by the later stages, so degradation of preamp tubes is more audible earlier than for power tubes. Once you have your rig finely tuned, where you know the feedback frequencies and how it sits with the rest of the band, etc., minor changes are much more noticeable. – Todd Wilcox Jan 01 '17 at 08:26
  • @ToddWilcox: OK, that's interesting, thanks for sharing your experiences. What I tried to point out in my answer though, is what I'd call the "average case", according to my own experience and my conversations with several amp techs over the years. They all confirmed that on average they replace power amp tubes much more often than preamp tubes, and that is also what I experienced with my own amps. I've had to replace power amp tubes in all of my amps, but there are at least two amps which still have their original preamp tubes (for about 10 years), and they still sound as they should. – Matt L. Jan 01 '17 at 09:44
  • BTW, is it only one specific amp that needs regular replacement of preamp tubes, or do you do that with all amps? – Matt L. Jan 01 '17 at 09:46
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    One thing no-one has yet noted is that the capacitors will also need changing after a while. The BBC used to do it every few years, on a schedule set when the equipment was purchased. [Can't remember now whether it was every 2 or 5 years] An old Fender Vibralux we had that no amount of valve changing would fix came back to its former glory after we swapped all the old 'chewed toffees' for modern electrolytics. – Tetsujin Jan 01 '17 at 10:32
  • @Tetsujin: You're right about the capacitors in vintage amps, but the OP bought a modern (and probably even new) amp, so it is unlikely that he needs to worry about capacitors any time soon. – Matt L. Jan 01 '17 at 10:55
  • I have owned four 100% tube amps in my life, one for over 20 years and another for over 15 and they have all been pretty much the same in this regard. I wonder what you would hear if you replaced your preamp tubes. Maybe I'm buying tubes that are cheap and wear out quickly. Maybe you consider the phase inverter to be a power amp tube while I consider it to be a preamp tube. I don't know. I definitely know how my amps behave. – Todd Wilcox Jan 01 '17 at 15:11
  • @ToddWilcox: No doubt you know how your amps behave; for me it's also not at all about being right or wrong. What I think is important here is to let the OP and other less experienced users know that *on average* they won't need to worry too much about replacement of preamp tubes, even though your personal experience is different. I collaborate with many pro guitar players in a teachers collective, and I regularly talk to different amp techs, and none of them would change preamp tubes very frequently (actually almost never ...) ... – Matt L. Jan 01 '17 at 17:09
  • @ToddWilcox: ... Nevertheless, your findings are very interesting and I will definitely bring them up the next time I talk to one of the amp techs I know. And I might even consider replacing the preamp tubes of one of my amps, who knows, maybe I just never noticed the changes in sound because they were so gradual ... – Matt L. Jan 01 '17 at 17:11
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    Tube don't have "moving parts" in the conventional sense -- yes the electrodes can move around under mechanical shock, but they don't have moving (mechanical) parts during normal operation. Also it might be a good idea to move comment about thermal shock (running the amp from a very cold state) into the body of the answer. – Dave Jan 01 '17 at 19:42
  • @Dave: Thanks for pointing out this inaccuracy; of course you're right and I meant it the way you understood it. Edited. – Matt L. Jan 01 '17 at 20:55