A few words on tubes, 1. Tube Life Expectancy, could be ten seconds, could be ten years, no guarantee, new tubes can be bad right out of the box, and high dollar, NOS, US or Euro tubes can fail just as fast a cheap China tube, it's alot like buying light bulbs. 2. Power Tubes, when replaced need to have the bias checked/adjusted/set, the bias must be set because it controls the current thru the tube, it affects tube life and the way the amp sounds, brand new high quality tubes won't make an amp sound great if the bias is not correct. Buycomp4, if you do get new power tubes , you will need to take the amp to a good shop and make sure they check and adjust the bias, pre-amp tubes are self-biasing so no worries there, ........
To answer TeleMaster, yes tubes are supposed to last a long time, some are designed to last over 10,000 hours of continous use, but we are faced with 2 major problems, quality control in manufacturing and the worst one of all, putting them in guitar amps, component failure inside the amp, power surges, rough handling and the use and abuse that guitarists knowingly and unknowingly put them thru takes a toll, if your tubes still sound great thats good but not everybody will have that kind of luck.........