Sorry for a real newbie question. I just bought my first tube amp that uses 6922 EH tubes. I am thinking of buying a few replacement tubes for future need. Can I buy any brand of 6922 - are they all the same? Or does it have to be the 6922 EH (which as far as I understand means Electro-Harmonix and most likely is a company name(?)) that came with the amplifier?
I also wonder if tubes wear out only when I play music or also when the amp is turned on (and the tube becomes hot).
Thanks in advanced sorry for the low skill. If my questions don't make sense, I appreciate getting help asking them properly.