Conrad Johnson Premier 140 6922 tube swapping

Although a bit off topic, I would suggest you make sure that amp has the upgraded film caps in the regulated power supplies. The old polystyrene caps have issues. If one shorts, and they do trust me, it takes out the whole regulator and it's not a pretty picture or a cheap repair.

If you can find matched Tungsrams they won't disappoint. What are the stock tubes?

Well I thought the 6922 I had in the 140 was a stock tube but it is a Electro Harmonix 6922

I had one of these--great sounding amp but mine was problematic--and rolled a few tubes in it. I even bought some vintage Tung-Sol 6550's which made an enormous difference, more than the 6922's. I thought the Siemens CCa was the best sounding 6922 variant but the Tungsram mentioned above is also good, as well as some Ediswans I bought at Upscale Audio.

That probably is their stock tube of choice. Very commonly spec'd tube. They don't totally suck - in fact, when mixed with NOS tubes in my SF Line 1 they do a fine job of adding bass slam.