You need to give us more info...Brand, Manufacture date, place of manufacture, etc.  Mark.

PS...I just realized you tell us that they are RCAs and looking at the old classified they would appear to be 1950's vintage. Does anyone use these in the Taboo or CSP3? What do they sound like? Mark.

Mark,

6BQ7As ...each make and vintage varies within their general sound. I have tried a number of them in my CSP3 with the stock caps and preferred them over 6N1P. They are generally more refined in delicate micro information. Some are more clear (like BVA Brimar), and some are pretty warm (like the early 50s RCAs I have). My DAC brings out a lot of micro detail, and I found all of the 6BQ7As I tried do notably better with this information than the workhorse 6N1P, while still having a pretty refined presentation across the spectrum. If you have tried 7DJ8/PCC88 the tendency toward micro detail seems similar.

With the Jupiters in my CSP3, so far tube choices are more difficult, those caps are so revealing and specific in their own sound. I don't really have a handle on them yet, but at one point in burnin, the Brimar 6QB7A I liked a lot with the old caps was a little too detailed and bright for me, but now it sounds quite real with an Amperex E188CC in front.

No way to tell without hearing this actual tube, but if you are looking for more micro information...inner detail, ambient info, and textures, the 6BQ7As I have heard will do this better than a 6N1P.

Yes, just one pair.