6CG7/6FQ7 experience/knowledge ?

[PeddlerPete]

I have 4 RCA's marked 6CG7 / 6FQ7, and some 'Ultrasonic' ones too.
Pin 9 is either NC or internal shield so will get grounded.
Pins 4/5 are the 6.3v heater filamet lugs.
http://www.drtube.com/datasheets/6fq7rca.pdf
Rated max 250v on the plates.
That must be the right page, 6FQ7...
I'm asking for theory, application or any other stuff I could know [such as 'yes/no'] before moving the filament supply lines around on the tube socket and trying it out in either preamp or PI position.