This week we have gone big! The mighty 845 (or it's equivalent the 211 or VT-43) is a directly heated triode.
Originally designed as a radio transmitter valve, now favoured by audiophiles, it has some massive stats. Listen to this, from the RCA data sheet:
Base: Jumbo 4 pin
Maximum anode volts: 1250
Anode dissapation: 100 watts!

The anode or plate is machined from solid graphite to avoid physical distortion at maximum power. To emit enough current the cathode filament consumes 3.25 Amps at 10volts and the recommended grid bias is a whopping -145 volts.

Because the cathode is thoriated tungsten, broken tubes should be treated with care. Thorium is both radioactive and very toxic.
Originally made by RCA in 1931, the 845 is still in production in China and now manufactured with either graphite or metal anodes.

Compared to most audio valves, the 300B or 2A3 is quite large. It is a directly heated triode capable of 40watts dissapation. This PS Vane example has a ceramic base for prolonged life. (The early bakelite bases were prone to crumble due to extended exposure to heat.
"In electronics the 300B is a directly-heated power triode vacuum tube with a four-pin base, introduced in 1938 to amplify telephone signals. It measures 6.4 inches high and 2.4 inches wide, and the anode can dissipate 40 watts. In the 1980s it started to be used increasingly by audiophiles in home audio equipment. The 300B has good linearity, low noise and good reliability; it is often used in single-ended triode (SET) audio amplifiers of about eight watts output; a push-pull pair can output 20 watts." wikipedia
I can be used as an output device in it's own right, or is commonly used as a driver for the larger 845 triode (coming soon!).