When it's time to change tubes? - And what tubes to buy?
I bought an used Marshall JCM900 2X12" combo a couple of months ago. It has 3 12AX7 and 2 5881 tubes. The guy that sold it to me bought it new in 1994 and never changed the tubes in it. He played it regularly but not everyday and not many hours.
My question is if it's time to change tubes in it or not. How do you guys discover that it is time to change the tubes in your amp? Does it loose volume, gain, high-end, bottom-end? I can't compare the sound that i now have with the sound when it was new, so i don't know if sounds very different or just the same. I just want to make shure that if i buy a new set of tubes i will actually hear some diferences in sound.
Also, i just asked a store about the models/prices of tubes and the store near me only has Sovtek and Groove Tubes. The GT's are WAY pricier than the Sovtek's. The guy in the store told me that the GT ones are made by Sovtek (they even have the Sovtek name on them!) but are choosen by GT (the best ones). The guy also told me that the differenece shouldn't be that much, so it would be better to buy the Sovteks.
What do you guys think? Are the GT's better than the Sovtek's? Will it be better to buy the GT's just because they are picked by GT? Are they worth the extra money?