Heater current aside, the 5687 is a drastically different tube, with half the gain of a 6922 and designed to run at much higher current. I can't imagine it would be a suitable drop-in for a 6922. There's no way to calculate how it would operate in your preamp without knowing the circuit involved.
Anyone use a 5687 with adapter in place of a 6922/6DJ8/7308/6N23P?
Have a small stash of original 1955 Raytheon 5687 (on contract to Sperry Gyroscopic Company for Us Air Force use) that are legit NOS/NIB. They sounded better than anything else of that tube type that I tried in a pair of monoblocks that I no longer have. Contemplating buying 2 of these adapters and running them in place of the 6N23Ps in a Dodd Battery Powered preamp.
Couldn't find anything on the Forum about this.
Anyone do this? What'd you think?
Thanks for any intel.