Musicians are already pretty bi-polar in regards to how they feel about their skill, it doesn’t help that there are so many variables involving equipment. This article is going to focus on tube amplifiers.
If your tubes are old, your tone isn’t going to sparkle, or have “life.” If you notice at some point that your once vibrant tone sounds cold and dead, there’s a good chance you need to replace your power tubes. Even if you don’t detect anything wrong with the sound of your tubes, if it’s been 8+ months you should replace them—you should be pleasantly surprised when you do.
Amp biasing is another variable often overlooked. This refers to the amount of voltage being allocated to the tubes in the amp. If you’ve never messed with this before, you can find tutorials online, however I recommend you take it to an amp technician and have him/her walk you through the process. It’s a task anyone is capable of doing, but there is enough voltage to kill so it’s not something to take lightly. You can find recommendations for different biases on the websites on any given brand of amplifier
Getting the most out of your amp’s EQ is essential. A common mistake is that if an amp is too shrill, guitarists just turn the treble way down. This is equivalent to throwing a blanket over your amp and muffling it. You need to let the amp breath, so let the treble come up a little bit and use the tone knob on your guitar to control the highs. Also keep in mind that less high end may sound good in your bedroom playing by yourself, but if you remove too much of it, you won’t be able to cut through a mix with a live band. What’s the point of great tone if nobody can hear it? Same thing if you use too much reverb, it might sound cool and airy by yourself, but your playing will have no definition once other instruments are introduced.
As always, remember to trust your ear. If you think something is wrong with your gear, you’re almost certainly right.