The first valves were invented by Fleming and de Forest, and were rather delicate items.
As this new device became better understood, its performance and reliability improved, notably with the use of a high vacuum.
In 1913 Alexander Meissner of Telefunken invented the first valve oscillator, just beating Franklin and Round, of the Marconi Company, who were close to similar discoveries.
This was the first step towards electronic transmitters and by 1919 high vacuum valves with reliable performance were in production.
Transmitting valves rated at several kilowatts became available and in 1920 Marconi was able to assemble the 100 kW transmitter shown here.
The time had come for radio communications to break out of long waves and sparks.