Originally Posted by xkonfuzed
Quoted from UpScaleAudio:
"Repeatedly tapping on a tube's glass can cause a perfectly good tube to become too microphonic for use.
ALL tubes are microphonic to a greater or lesser degree. Whether or not that microphonics is audible will depend more on the tube's function in the product, rather than the microphony of the tube itself. In some positions, you will never hear anything, even with the worst tube. In other positions you will hear something even with the best tubes. At that point you make a judgement call: does this level of microphony interfere with my listening enjoyment?
Tubes are supposed to make noise when tap you tap on them! If a tube is truly microphonic, and in a position where it is critical, you will know it. It will feedback as you play music and be so objectionable you'll turn it off."
Also, generally speaking, tubes logos are made of ink that will fall off easily. So when you keep touching it (especially when its hot), the logo will go away.
Sorry, but that's pretty much all balognea.
I've played guitar for many many years and have owned many tube amps. No tech, roadie, or guitar player wears gloves when changing tubes. It doesn't do anything if you touch the tube either.
That theory comes from electricians who said you shouldn't touch a halogen lightbulb with your bare fingers. Otherwise, you'll leave oils that will burn that part of the bulb quicker which will weaken the light and change its structure. Handling tubes with bare fingers is perfectly fine.
As for microphonics, gently tapping a tube with a pencil is an age-old way of testing this. Though every tube is subject to microphonics, great tubes will test in a way that microphonics are beyond human hearing, which means that they're essentially micrphonics-free... but they can develop microphonic qualities over time.
Nevertheless, I wasn't complaining about the tube being microphonic but rather that the sound becomes distorted after a few minutes. When I test it with another tube, I'll see if the problem is eliminated or not.