A pair of 6922 pinch waist: $1800+
These are for many the Holy Grail of all Holy Grails. Here's what Brent Jessee has to say about the Holland made Valvo Cca Pinched Waists...starting about half way down. These are also the first year production of the pinched waists which had the added caveat of having gold internal wiring (supposedly) for reportedly a richer sound. Read it and weep.
Whew, these babies are so scarce there isn't even much info out there about them! Mentioned by audiophiles, usually in a reverent whisper, these gold pinned gems are about as good is it gets in 6DJ8-land. Matched triode sections, low noise screening, 10,000 hr. heater life expectancy, carefully controlled frame grid winding, low microphonics......the list goes on and on. This is regarded as one of the most detailed and three-dimensional sounding tube ever made in this family of tubes. Most of what is available is Siemens or Telefunken made, although there are a few very rare examples of Philips or Amperex Holland made out there. Since this was a tube made specifically for the German goverment and military, all that I have seen carry a German brand label, even those made in Holland. Even rarer are the Holland made Cca tubes with the pinched waist indented glass midsections, said to be the most sonically "3D" tube ever made, of any type. Finding these is akin to finding a 1795 gold piece in your attic! I don't believe there were any of these Cca tubes made in the USA. Awesome audiophile tubes! Yes, they are costly, but like most top flight NOS audio tubes, you get what you pay for. These Cca tubes will give you more improvement in sound than upgrades like expensive speaker cables that can cost 5 times as much as a pair of Cca tubes!
There must be diminishing returns. I think it is mostly the rarity as well as supply and demand for collectors. Probably more for investing then use.