#1
How often do you have to change the 2 12AX7tubes of the tube driven spring reverb of an amp???
#2
Two tubes? Should just be one. A 12AX7 has two triodes inside it. They can last years or not long at all. They are traditionally a cathode follower driver so some tubes in there will die quite quickly. I wouldn't put a Sovtek in there. If it's a JJ or a SED or something good you'll get a few years out of it usually. A NOS one could last decades.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#5
Preamp tubes can last a very long time indeed. I have 30 year old Indian BEL 12AX7's (made by Mullard) that are still going strong in one amp. If you stick to good quality ones like JJ you should get a couple of years out of them.
Here's what you do. You have spares, at least one. When you think your amp is sounding a bit "off" you try your spares in different positions and hear how it sounds. You've just diagnosed the state of the old ones by a comparison test.
It's that easy.

Power tubes: depends how hard you push them. A good year or two or so depending on the tube. You test them the same way - have spares. You'll want to rebias them as well though which complicates things a bit.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Dec 14, 2011,