I have been designing a 1626 headphone amplifier based on Lloyd Peppards (Mapletree) ear+ amp and needed parameters for the 1626 tubes to input into TubeCAD. The available spec sheets for these tubes provide little information on mu, GM, RP and such. It is even conflicting between manufacturers. This is probably due to them not being designed or used in audio circuits. Anyway, I decided the best thing to do is measure the parameters on a sample of tubes myself at the operating point of interest.
I chose to test the 1626 tubes with centerpoint values of VP=200v and IP=15ma. I tested 4 1626 tubes that Shannon got from the Peoria Superfest last year. They are branded National Union and have identical markings and date codes. The averages for 4 tubes are as follows:
mu = 5.075
GM = 1671
RP = 3049
These tubes all tested very close to each other, so the standard deviations on the mean values are very small.
JT