here is a space i can use to share reference info.
here are some etracer sweeps of subminis and rare tubes:
i really love subminis, although they are even less to look at than 9 pin and 7 pin minis…
the 6247 is fabulous mainly because it’s built to have very low mechanical noise. the transconductance is low for my taste so i use it in a hybrid composite amplifier.
the 5744 is my other fave. they are similar but taste different. i like it for preamps and guitar effects.
baffle shape and diffraction: from Olsson
critical research from Small:
nasty comments by Augspurger
below, an image from Landee, Davis, and Albrecht… concerning the input reference for grounded cathode amplifier stages. this is the seed from which all my “upside down” circuits come from.