Valve amplifier thermionic valves. The simplest valve was invented by John Ambrose Fleming while working for the Marconi Company in London in 1904 and named the diode, as it had two electrodes. The diode conducted electricity in one direction only and was used as a radio detector and a rectifier. In 1906 Lee De Forest added a third electrode and invented the first electronic amplifying device, the triode, which he named the "Audion". This additional "control grid" modulates the current that flows between cathode and anode. The relationship between current flow and plate and grid voltage is often represented as a series
955 acorn triode current is 4.5 mA at a voltage of 180 V with an anode load of 20 kilohm. The 955 is designed to be used in the frequency range of 60–600 MHz (5-0.5 metres wavelength). The amplification factor obtained is between 20 and 25 depending on details of the specific stage design and operating voltage. 955 acorn triode The type 955 triode "acorn tube" is a small triode thermionic valve (vacuum tube in USA) designed primarily to operate at high frequency. Although data books specify an upper limit of 400–600 MHz, some circuits may obtain gain up to about 900 MHz.