My AC15 is running Groove Tubes (re-badged JJ’s) which the previous owner installed for power tubes and a Sovtek and JJ mix for the preamp. I like the JJ’s better in the power section than the stock Sovteks. I like the Sovtek in the preamp though, although it has to be the 12AX7-WC Sovtek and not the more common 12AX7-WE which comes stock in most amps. The 12AX7-WC is a much better sounding tube than the more common 12AX7-WE.

A set of NOS (New Old Stock) or even UOS (Used Old Stock) Mullards will last you the lifetime of the amp. From that aspect many people see them as a worthwhile investment, rather than re-tubing with current production valves every couple of years.

Yeh, the lifespan of NOS tubes if far superior to current production stuff. They don’t make them the same as they used to, even though many new companies use the same factories and manufacture with the same gear. For example, JJ valves are manufactured in the old Tesla plant.

The reason why, that I’ve heard/read, is that the companies these days don’t vacuum the tubes as much as they used to. This results in a reduction of the lifespan of the valves, as well as a change in the how the valve sounds. I’ve only heard/read this theory, but it makes sense.

Back in the day everything used valves as it was the only technology around, so they were always in demand. It didn’t matter if they lasted many many years, because there was always a constant demand for them. These days only audiophiles and guitarists use valves, so the market is smaller now. If current production valves had the same lifespan as NOS ones, companies would go broke as people would be buying valves too infrequently. There’s probably other factors involved too, like the materials being used etc, but I did always wonder how current production tubes and NOS tubes sounded so different, when they are supposedly made in the same plant.

The Sovtek 12AX7-WC has slightly more gain than the other Sovtek variants. Sound wise they are described as being a bit more ‘richer’ in their sound compared to the rest. As with most things it’s all subjective, as it depends on the amp it’s being used in too.