There must be 100 tonnes of EF80 or 6BX6 lingering forgotten and
unwanted around the world.
Many were made for the TV IF stages of tube TVs.
But they make fabulous triodes, imho.

Any chance of doing a test on those?


Just be sure that you use "sharp cutoff pentodes".
Some TV IF pentodes were "remote cutoff". Variable
gain depending on bias. Great way to do AVC, but
not good for audio work.

Some TV tubes were "dual control" pentodes, and
heptodes (pentagrid). One could use one grid
to feed audio, and the other grid to vary the
gain via a DC bias of the plate circuit.

http://pw2.netcom.com/~wa2ise/radios/elvctube.jpg
http://pw2.netcom.com/~wa2ise/radios/6be6vol.html