Preamp tube questions

[Snow006]

I know when a preamp tube is at the end of its life it can sound horrible but what about when people advertise it at like 65% or 90%? Does it sound the same as when it's new? Does it gradually degrade in sound quality as it's used?

 

[bandit2013]

It can vary, but with normal use and without an abnormal issues or circumstances (plate voltages or cathode followers) it will just degrade gradually over time. Some symptoms may be reduction of top end or reduced bottom end. Gain reduction may also be noticed but may not be dramatic. Sort of like using old guitar strings as they seem to loose there chime.

I had owned my Mark IV for 12 years without changing any of the tubes in it. I did not use it all that much, perhaps for the first 4 years I did but had to give up playing for a while to heal from an injury (took about 8 years actually). All the tubes had 4 years of mild use and sounded great when I got back into it in 2012. It was not until I got the Mark V that I realized the preamp tubes need replacement.

Preamp tubes can last a long time in non-cathode circuits. I still have all of the preamp tubes from my band days (replaced all tubes every 3 months which was usually the life span of the 6CA7 when used in the Mark III). That was back in the 1990's. Preamp tubes are still good and I am using them in some of my amps. Too bad the power tubes were no good as those were RCA and Sylvania's. I think it was around 1992 when the good power tubes went scarce as the surplus dried up.