Difference between Amperex 6922 pinched waist tube

You hit the nail on the head, the pinched waist are considered the holy grail of the 6299 family. Depending on the function of this tube in your gear you may not notice much an improvemento over the CCa which is head and sholders above the standard E88CC, which in and of its self is better than anything else in that type. other tubers may beg to differ but that is part of the wonderful world of tube amps.

Of the pinch waist tubes there may only be 6 or 7 left on the planet in NOS shape. Unless your are Bill Gates it may not be worth your while chasing them down. Be thrilled that you have the CCa types.

My ears, my gear, MHO....YMMV

My advice is only second hand from a pro tube dealer I use from England. I own the Siemens 6922 but not the CCa but even the standard West German one is perhaps the best of my growing collection, I just purchased a A "Marconi" = Mullard E88CC. A very different sound indeed. This is what he had to say on your question:

"The gold plated grid posts ,the pinched shape and the scarcity probably increase the 'tube ego' of the owner rather than please the user with the sound ;) I can't remember if I mentioned it before but I am certain one of the favourite 6DJ8 Ihave tried was the CV2493 otherwise known as theE88CC-01 . These were actually made to be better rather than selected like a CV2492/E88CC/6922/CCA"

That being said I have yet to find any CV2493s for sale-

Based upon the last comment made about 'tube ego'I must tell you that a very good friend of mine recently dropped 1350 US dollars on a total of 9 tubes.These were 6 TELE 6922 cca's and 3 regular low noise 6922's.He has the same pre-amp as me,a highly modified,Audio-Research SP-15.This takes only 3 tubes for the phono stage,and after the almost total re-build of the unit by GREAT NORTHERN SOUND,a mod specialist on audio research stuff,the performance went into the stratosphere.UNTIL he replaced his MULLARD's with the new HIGH PRICED SPREAD,which were cold,and thin.Actually they sounded dreadful!However to justify his purchase,and knowing I was coming over later that week,for a listening session,all he kept talking to me about was how GREAT the new tubes were.Needless to say,he got rid of all nine tubes(one set,and two back up sets)and went on to purchase,again, they had to be REALLY expensive or they could not be acceptable,to him, the most costly gold pinned Mullards he could find.Which are better than the previous batch,but,unless you are willing to do some 'tube rolling'you will never know!