HT (vacuum tube)
Encyclopedia
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In vacuum tube
technology, HT or high tension describes the main power supply to the circuit, which produces the current between anode
and cathode
. It is also known as the plate supply or voltage, B battery supply, or simply labelled ->B on circuit diagram
s, from the days of battery powered circuitry.
EHT or extra high tension similarly describes the accelerating voltage for a cathode ray tube
such as used in a television
, computer monitor or cathode ray oscilloscope.
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 furnace
s 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:
s, the EHT supply was typically generated by rectifying the output from the scanning circuitry rather than directly. Specialised efficiency diodes, also known as damper diodes or energy recovery diodes were produced for this application.
In vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
technology, HT or high tension describes the main power supply to the circuit, which produces the current between anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
and cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
. It is also known as the plate supply or voltage, B battery supply, or simply labelled ->B on circuit diagram
Circuit diagram
A circuit diagram is a simplified conventional graphical representation of an electrical circuit...
s, from the days of battery powered circuitry.
EHT or extra high tension similarly describes the accelerating voltage for a cathode ray tube
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
such as used in a television
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
, computer monitor or cathode ray oscilloscope.
The HT supply circuit most commonly provides a positive
Electrical polarity
Electrical polarity is present in every electrical circuit. Electrons flow from the negative pole to the positive pole. In a direct current circuit, one pole is always negative, the other pole is always positive and the electrons flow in one direction only...
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 furnace
Electric furnace
- Music :* Electric Furnace , a Welsh heavy metal band.An electric furnace may also be any of the following type of heat producing equipment using electric power:* A central heating plant for a home or building...
s 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
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
).
Other power supplies to vacuum tube circuits include:
- LT, low tension or A battery, the supply to the heater filaments. If directly heated vacuum tubes are used, there might be several of these. For example, in mains-powered equipment directly heated full-wave rectifier tubes such as the 5Y35Y3The 5Y3 is a medium-power directly heated rectifier vacuum tube introduced by RCA in 1935. It has found wide use in tube radios and early guitar amplifiers It is virtually identical, electrically, to the four-pin type 80 tube, but with an octal base.The success of the 80 and 5Y3 led to the...
commonly provide the HT supply, and required a devoted, often 5V, heater circuit. For other tubes, 6.3V was common, later replaced by 12.6V for 7-pin and 9-pin base valves such as the still popular 12AX712AX712AX7 is a miniature dual triode vacuum tube with high voltage gain. It was developed around 1946 by RCA engineers in Harrison, New Jersey, under developmental number A-4522. It was released for public sale under the 12AX7 identifier on September 15, 1947. The 12AX7 was originally intended as...
. Some specialised battery valves had 2V heaters. - GB, grid biasGrid biasGrid bias is a DC voltage applied to electron tubes with three electrodes or more, such as triodes. The control grid of these devices is used to control the electron flow from the heated cathode to the positively charged anode...
or C batteryC batteryThe C battery is a standard size of battery typically used in medium-drain applications such as toys and musical instruments.As of 2007, C batteries accounted for 4% of alkaline primary battery sales in the US...
. Used mainly in battery powered equipment; In mains powered equipment the tubes are more commonly self biased. - EHT or Extra High Tension, the accelerator supply to a cathode ray tubeCathode ray tubeThe cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
, normally negative to supply the tube cathodeCathodeA cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
in order to keep the screen at near chassis potential. This supply typically ranges from 15 kV to 35 kV.
HT
EHT
In vacuum tube television setTelevision set
A television set is a device that combines a tuner, display, and speakers for the purpose of viewing television. Television sets became a popular consumer product after the Second World War, using vacuum tubes and cathode ray tube displays...
s, the EHT supply was typically generated by rectifying the output from the scanning circuitry rather than directly. Specialised efficiency diodes, also known as damper diodes or energy recovery diodes were produced for this application.
External links
- http://www.earlytelevision.org/damper.html Early Television Museum article on efficiency diodes