I have a big box full of these but I have only done some basic testing. This tube is rated for audio amplifier use, but I didn't try to use it as a power amp because I have a lot of other tubes that will make more power. I tried it as a cathode follower driver tube. It worked OK but the 12BY7 worked better. I will try it as a voltage amplifier at a later date.
It could be used for a low power amplifier, maybe 1 watt SE triode, 3 W SE pentode, maybe 10 W PP pentode. I would try 200 to 225 volts of B+ maybe 250 with cathode bias. The data sheet shows a 9K ohm load in SE pentode mode. If you want to experiment with this tube, try an EL84 circuit, with lower B+ voltage.
I figured that the other parts for the amp would be worth more than the tubes, so if you were going to buy all of the parts for this amp, then spring for some EL84's. If you have the parts to experiment, then try it. I have a larger box full of 6AQ5's so I am experimenting with them instead.
One more thing, these tubes like to oscillate. Use grid and screen stoppers.
Too much power is almost enough! Turn it up till it explodes - then back up just a little.