I did a lot of research over the years on the various Siemens E88cc tubes. The famous Cca and E88cc from Siemens were made identically. The only difference was that the Cca were hand selected for low noise for the German postal service. Otherwise, they both sound identical. The secret is to find either one made from 1959-1965. The best ones have a dimpled getter support( although some have no dimples) with codes etched on the glass or plate of support of three lines, reading vertically of A12, A13, A14, and A15. The A16 and A17 don't sound as good. I read this from users on the Tube Asylum and have proven it to myself. It is also important to find one of these models that has high emission rate with low, noise, zero microphonics, and no shorts or emission leaks. I spent a lot of money for an early pair of Siemens Cca a few years ago and they sounded terrible because of noise and emission leaks. I bought an inexpensive tube tester to test all tubes that I buy to make sure that they meet the seller's ad specs. Also, beware of fake Siemens tubes. A good eye can spot these fakes. In any event, once you find the right Siemens E88cc, you will have many years of wonderful music before they lose their emission strength and you have to buy another pair or more. I have a quad in my back-up that should hold me until I'm playing the trumpet in Heaven.
