The normal dual triode adapter card only tests one 12AX7 (or any dual triode with similar pinout) at a time. That's great for matching both sections within a single glass envelope, but what about matching separate tubes?
This is possible with a fancy adapter card. You can build this yourself using a blank adapter, some switches, and a lot of wire. This card is for matching both "A" sections of two tubes or both "B" sections. You must use the normal dual adapter card for matching "A" and "B" within the same tube. Basically, match within a tube first, then match to other tubes. This is useful when you need matched quads.
Here's the schematic:
It's a bit ugly, but we're mostly interested in useful functionality here.