Before revision: The high working voltage makes them well suited for radio transmitters and valves remain in use today for very high power short wave radio transmitters, where solid state techniques would require many devices in parallel, and very high DC supply currents.
After revision: The high working voltage makes them well suited for radio transmitters and valves remain in use today for very high power short wave radio transmitters, where solid state techniques would require many devices in parallel, and very high supply currents.