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I heard literally everywhere that it is really important to let my amp warming up for some minutes before playing the guitar (or give some audio do the input).

Strange thing is that the recommended time is different everywhere ! I red between 30 sec and half an hour...

I did not find any other physical/electrical reasons than "the tubes have to warm". In my opinion there is a lack of true scientific explanations, it's seems more like a blindly believing. What are the risks if tubes are stimulate directly at startup ? And why these hypothetical risks even exists ?

Lot's of guitarist seems to don't care about it and directly play whithout reporting any issue.

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  • Related anecdote - Richard Feynman as a child "fixed a radio just by thinking." He listened to startup static and realized the output tubes were warming up faster than the input tubes (same model) and swapped the tubes.
    – Carl Witthoft
    Commented Feb 24, 2020 at 16:54

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The way tubes work is that electrons are "boiled" out of the cathode by heating it, and then pulled across to the anode by the different voltages inside the tube.

The only way you can damage a "cold" tube is by applying so much voltage that you pull the electrons out of the cathode "by force" and physically damage the cathode material permanently.

Note, one way to apply excessive voltage to a tube is to use the amp with no speakers connected. If a properly designed modern amp has the correct impedance speakers connected it should be impossible to damage the tubes with over-voltage.

Unless you have an insanely high powered tube amp (which will probably have special start-up procedures anyway) and if you use modern tubes, the risk of physical damage is negligible, and if you try to play in the few seconds before the cathodes heat up, you will simply get no sound output.

The situation was a bit different with old tube amp designs (e.g. from the 1950s) where the power supply also used tubes not modern semiconductors, and various bad things could happen while the power supply tubes themselves were warming up, but that is now history.

Of course musicians with golden ears may claim their amp sounds different after a 30 minute warm up, but that isn't the same as "damaging it".

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    Of course, those golden-eared musicians may also claim that cleaning the tubes on the outside affects their sound, particular when done during full moon...
    – leftaroundabout
    Commented Feb 22, 2020 at 9:55
  • The values of some electronics components vary with temperature. For capacitors the change may be a few percent between room temperature and operating temperature. It's not much, but I wouldn't completely rule out that someone could hear the difference.
    – ojs
    Commented Feb 22, 2020 at 22:20
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    @ojs yes, it's not inconceivable that this could have a significant influence. My point was just that musicians are a notoriously unreliable source to tell about such effects.
    – leftaroundabout
    Commented Feb 23, 2020 at 0:34
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A certain amount of heat in a tube amp is a good thing. Tubes do need to warm up to function properly, but the warm up time is minimal, a minute or two is satisfactory, after that you're just wasting electricity if you're not playing through the circuitry and making music. Keep in mind that it's possible to have to much heat in a tube amp and burn up components like tubes, resistors, wiring and transformers. Therefore, I don't subscribe to such blanket statements as "it needs to warm up for thirty minutes before you play". Instead, I find the amp needs a short warm up and then you can enjoy playing it. There are players who achieve a particular tone or effect by pushing the limits of the capabilities of their equipment. That's fine, but you should understand the toll it can take on your equipment if you choose to abuse it in such a manner.

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  • This does not bring anything to the question. "... a good things" seems completely arbitrary and subjective. You said a minute or two but on what do you rely to said this ?
    – Welgriv
    Commented Mar 3, 2020 at 12:39
  • @Welgriv- My answer is based on my own experience, study, and several years of design, repair, and rebuilding old tube amps and playing them. You may take this information or leave it, it's your choice.
    – skinny peacock
    Commented Mar 3, 2020 at 14:07
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In my (admittedly limited) experience with tube amps, they simply didn't work before they were warmed up. No signal came through. So anyone who tells you to let an amp warm up for 30 seconds probably has that in mind. The amp I had the most experience with was in a public address system, and the usual way of checking whether it was warmed up was to talk into the microphone until the sound came out at the speaker. I don't think the tubes were replaced very often, if ever, so I doubt they were damaged by this practice.

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