I was looking at some old 813 tubes that were once commonly used for
Amateur radio transmitters, as the final output tube. While the common
audio output tubes like 6L6 and 807 can produce about 25 to 30 watts
audio output (per tube), running around 300 to 450 volts plate voltage,
this 813 tube is rated at 250 to 300 watts output RF (per tube), but
running at around 700 to 750 volts on the plate.

I'm not planning to do this, but if this 813 tube was used in an audio
amplifier, and using 700 +/- plate voltage, would this tube be able to
put out around 250 to 300 watts audio power (per tube)? Yea, I know it
would require a custom audio output transformer.

Just curious.....