My Siemens 6922 listening experience with ARC gear is extensive and the answer is simple: in a revealing system, good well matched examples (see below) smoke current Russian 6922's in almost every respect - detail, dynamics, imaging and transparency, among other things. Getting there, on the other hand, is another story. Siemens 6922's come in at least four versions that I know of and the vintage is also important. The four versions are, in ascending order of sound quality, ECC88, E88CC, 7308 (=E188CC) and Cca. In terms of vintage, strictly speaking, the name "Siemens Halske" refers only to the older production tubes from the '60's, while the later 70's/80's versions came in boxes labeled "Siemens Rohre". I have also seen military versions of the E88CC and 7308 labeled JAN or with a falcon logo on the tube. In terms of sound, though, the real distinction is between the getters: the earlier reputedly better sounding versions have a grey chemical coating on them - 'grey' getters - and the later ones have clear metal ('silver') getters. Good well matched examples of grey getter versions are now almost impossible to find or assemble; 70's versions are still around and I highly recommend them. Testing and matching is critical; I wouldn't go into any NOS tubes without my own tube tester. The first and simplest test is for output level, which is measured as transconductance, because the output of every tube declines with hours of usage. 6922's have two sections which have to be measured separately for output. Unbalanced gear often - not always -employs these tubes in pairs with one tube to a channel, so that the aggregate output of each tube in the pair should be the same ('matched'). Balanced applications generally require that each section of each tube have the same output(!) The next issue is microphonics, which is a particular problem with 6922's; it can be due to a manufacturing defect or from mishandling (these tubes are 20-40 years old). The crude way to measure is that you can hear it by tapping the tube while the gear is on; some testers (Vacuum Tube Valley ("VTV"), Hickock 539C) allow you to listen for it. Microphonics is less important if the tube is not used in a high gain application, but I personally would not use a microphonic preamp tube in a cutting-edge system. VTV has also developed a test for triode to triode plate balance. Current production tubes are not spec'd to have balanced plates, but premium NOS versions were, so I believe that test is also useful. This is a long primer, perhaps, but I learned most of this stuff the hard way. Happy tubing!
