TUBES 6922 pinched waist

Try Andy @ Vintage Tube Services. His phone number is on his web site-www.vintagetubeservices.com He should be able to give you the history of pinched waist tubes. He told me that it was a further attempt by some vacuum tube manufacturers to reduce microphonics. A roller was used on the glass to give it the pinched look and they were only manufactured for a few years. I think that if you can find any, they will be outragously priced. Andy told me that he has only run across one pinched waist tube. As far as 7308 tubes go... I've been told that they were an attempt by manufacturers to make a hardier tube than the 6922. I run 7308 Amperex white label/shield tubes in my preamp. I like their sound, but I haven't done that much tube rolling. I believe that they are a tougher, longer lasting tube. Andy should be able to give you a seasoned opinion of 7308's as well. When it comes to knowledge, he's the man! Good luck! Stan

Yes, my 7308 vacuum tubes have a shield around the "pq" on one side of the tube. On the opposite side of the tube, it's labeled "Amperex 7308 USA." They made a Holland version of this tube, but I've never tried it. The Holland version is sapposed to be a little sweeter. I've noticed that these tubes are starting to get expensive as well. I've got 4 matched sets of 7308 Amperex PQ white label with shield in my preamp. With that many tubes needed, tube rolling is kind of out for me.

Gellis1, I thought I'd add that Andy @ Vintage Tube Services does testing as well. He has a lot of the old testing equiptment-pictures on his web site- dating from 1920-1960. For $6 a tube, he can test your tubes for use-(how close they are to being new), shorts, etc. and tests them in a testing booth for microphonics. I had him test a batch of new 1976 7308 Jan Sylvania tubes that I stumbled upon in my area. He matched the survivors, which was about half of the tubes sent, labeled them and sent them back. Also, if you do buy tubes from him, he backs them up for 1 yr. Good hunting! Stan