vacuum tube A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. The type kn ...

technology, HT or high tension describes the main power supply to the circuit, which produces the current between

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...

and

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in whi ...

. It is also known as the plate supply or voltage,

B battery A generic triode vacuum tube circuit showing "A", "B" and "C" batteries">vacuum_tube.html" ;"title="triode vacuum tube">triode vacuum tube circuit showing "A", "B" and "C" batteries In the early days of electronics, vacuum tube (called ''valves' ...

supply, or simply labeled ->B on circuit diagrams, from the days of battery powered circuitry. The HT supply circuit most commonly provides a positive voltage of some hundreds of volts to the anode (or ''plate'') and in later circuits also to the screen grid, with the cathode running at near ground or chassis potential. The main exception to this was in the case of tubes with water-cooled anodes, once used for radio transmission, electric furnaces and similar applications. These tubes used a negative HT supply to the cathode, so that the anode could run near ground DC potential (but typically at many hundreds of volts of RF). Other power supplies to vacuum tube circuits include: * LT, ''low tension'' or ''

A battery A generic triode vacuum tube circuit showing "A", "B" and "C" batteries">vacuum_tube.html" ;"title="triode vacuum tube">triode vacuum tube circuit showing "A", "B" and "C" batteries In the early days of electronics, vacuum tube (called ''valves' ...

'', the supply to the filaments or heaters. Early tubes designed for battery operation had 2 volt filaments (for use with a lead-acid cell). Later tubes had 1.4 volt filaments to run from dry batteries. With the introduction of mains powered equipment, indirectly heated tubes became more common and usually (though not always) required 4 volts in Europe and 6.3 volts in America. The latter became the standard voltage after the

Second world war World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

. One notable exception was that rectifier tubes often had 5 volt filaments or heaters which usually had to have a separate supply anyway. * GB, '' grid bias'' or '' C battery''. Used in early battery powered equipment. Once self biasing circuits were developed, this power source was no longer required. * EHT, ''extra high tension'', the accelerator supply to a

cathode ray tube A cathode-ray tube (CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen. The images may represent electrical waveforms ( oscilloscope), pictu ...

. This supply typically ranges from 15 kV to 35 kV, though very early television receivers used voltages as low as 4 kV.

Typical circuits

HT

The HT supply was usually obtained from a full wave rectifier circuit similar to the one shown. In those sets that had no mains transformer (the so-called

AC/DC AC/DC (stylised as ACϟDC) are an Australian Rock music, rock band formed in Sydney in 1973 by Scottish-born brothers Malcolm Young, Malcolm and Angus Young. Their music has been variously described as hard rock, blues rock, and Heavy metal ...

design), the HT was obtained directly from the mains supply, either with a simple half wave rectifier or with a

voltage doubler A voltage doubler is an electronic circuit which charges capacitors from the input voltage and switches these charges in such a way that, in the ideal case, exactly twice the voltage is produced at the output as at its input. The simplest of thes ...

circuit.

EHT

In very early vacuum tube

television set A television set or television receiver, more commonly called the television, TV, TV set, telly, tele, or tube, is a device that combines a tuner, display, and loudspeakers, for the purpose of viewing and hearing television broadcasts, or using ...

s, the EHT was derived directly from a high voltage winding on the mains transformer using a half wave rectifier. In later television sets, the EHT supply was invariably generated by rectifying the flyback pulses from the scanning circuitry rather than directly from the mains supply (a practice that survived the transition to transistor circuits). Although this provided a greater degree of safety, the reason for the change was that the mains transformer had been eliminated from sets produced from the 1940s onwards.

External links

* http://www.earlytelevision.org/damper.html Early Television Museum article on efficiency diodes Vacuum tubes