The State of Vacuum Tubes for the 21st Century
Have a look at this, guys. It is extremely interesting for anyone who uses valves!
http://www.vacuumtube.com/FAQ1.htm
I found this bit particularly interesting regarding NOS and current production valves:
Quote:
TQR: In terms of audio quality, durability, and technical performance, how would you rank the various manufacturers previously described?
VTV: I feel that NONE of the current production is exactly as good as genuine premium NOS tubes from Western Europe or the USA. Part of the sound of a really good tube is caused by ultra-pure cathode materials--something Western Electric, M-OV, and other firms strove to use whenever possible, for longevity. You chances are, you will NEVER see that done again, the economics of OEM tube sales won't allow it.
The largest buyers of tubes are the big guitar-amp makers; Fender, Marshall, Ampeg, Mesa, Peavey and a few others. They drive the market, and they have collectively made it clear that their primary qualification for a tube for use in a guitar amp is low unit cost. They go around shopping for the cheapest tubes which give tolerable reliability in a guitar amp. Many amp companies design their amps around, say super cheap Chinese 6L6GCs and they work just fine. Cathode purity is not important.
As far as VTV's editors can tell, very few guitar amp makers pretest tubes to find the longest-lived version or brand. Another issue is with cleanliness and vacuum hardness. This is easily traded off at the factory, and the end-user often can't tell--until the tube outgasses and its plate current runs away, destroying the amp! All the current factories are pumping their tubes down for the shortest time they can get away with. Because guitar amps stress the screen grids of output tubes, one can see this as a problem for reliability.
When a screen gets red-hot, any absorbed gas in it will be emitted. Enough of it, and the tube runs away. Again, OEMs are demanding low cost and quick delivery schedules, so the tubes are not pumped for 2 or 3 hours, as the best factories once did routinely. This is less of a problem with power triodes like 300Bs, but those are not used in guitar amps. Preamp tubes aren't much affected by gas, except for its tendency to shorten cathode life.
That'll explain why I much prefer the sound of genuine NOS valves, and the older the better! :smoking:
But that's just the tip of the iceberg - there's so much great info within this link it's mesmerising!
Marco.
