Tbone: I usually go to the Audio Asylum tube forum (which has a full search feature) to research tubes that I am not familiar with. The combined body of knowledge of the members (or inmates as they refer to themselves) is quite impressive. I have some 5687's with the WA added at the end, but have never looked into it. I have learned to judge each signal tube based on its sonic qualities in my setup and label and store them accordingly for future use. I have some cheap RCA black plate 5687's that blow away the rather pricey Sylvania Gold Brand ones that I also use. I have also not found any rhyme or reason (brand and vintage) as far as sound quality with 6922 tubes either as long as they are not new production Sovteks which all sound kind of lame. Each brand has a general signature sound, but there is a lot of variation to my ears between like tubes that test the same. I run a signal tube for 2-3 days before making notations and moving on to the next one. I also audition them with both JJ and Svetlana output tubes to see whether they work best with a bright (JJ) or soft (Svetlana) setup. The synergy between the signal and output tubes can make or break the overall sound, if you use both in the same application. I plan on using the best sounding combinations first while I still have my hearing. Sorry that this does not directly answer your question, but thought you might be interested in what I feel is a sound approach to procuring and stockpiling tubes for future use and this method may open up the purchase of less sought after tubes (less expensive) that will sing in your system just the same.
