173:
AC power, the neutral, rather than live, line should be connected to the chassis; touching it, while highly undesirable, is usually relatively safe—the neutral conductor is normally at or near earth potential. But if used with a two-pin power plug (or an incorrectly wired three-pin one), any metal that the user could touch was an electrocution hazard, connected to mains live. Consequently equipment was made with no metal connected to the chassis exposed even in predictable abnormal situations, such as when a plastic knob came off a metal shaft, or small fingers poked through ventilation holes. Service personnel working on energized equipment had to use an isolation transformer for safety, or be mindful that the chassis could be live. AC-only vacuum tube equipment used a bulky, heavy, and expensive transformer, but the chassis was not connected to the supply conductors and could be earthed, making for safe operation.
221:(high tension) supply. In a typical vacuum tube colour TV set, the line output stage had to boost its own HT supply to between 900 and 1200 volts (depending on screen size and design). Transistor line output stages, although not requiring supply voltages above the rectified mains voltage, nevertheless still developed extra voltage over the normal supply rail to avoid complicating the power supply circuitry. A typical transistor stage would produce between 20 and 50 'extra' volts. Some details of the way in which the nominally 190 volts HT supply was boosted to nearly 500 volts in the 1951 Bush TV22 are described in a technical publication. AC/DC televisions were produced well into the color and semiconductor era (some sets were tube/semiconductor hybrids).
81:. The sole aim of the design was to eliminate the mains transformer. The lower cost of transformerless designs remained popular with manufacturers long after DC power distribution had disappeared. Several models were produced which dispensed with the power transformer, but had circuit features which only allowed operation from AC. Some early models were available in both AC-only and AC/DC versions, with the AC/DC versions sometimes slightly more expensive.
88:. All pre World War II sets used mains transformers and consequently were AC only. In 1948 Pye released the first television receiver, the B18T, to employ the AC/DC design to eliminate the mains transformer when operated off 240 V mains. While sufficient for radio, the voltage was not high enough to power some television circuits, so energy was recovered during the flyback period from the primary of the
130:
additional resistance and the voltage drop across it could be quite high, and it was common to use a resistive power cable (mains cord) of defined resistance, running warm, rather than putting a hot resistor inside the case. If a resistive power cable was used, an inexperienced repairer might replace it with a standard cable, or use the wrong length, damaging the equipment and risking a fire.
258:
20:
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which was connected to one side of the mains. Because no power transformer was used, "hot chassis" construction was required: one of the mains power lines became the negative side of the power supply, connected to the chassis, and all metal parts in metallic contact with it, as common "ground". With
212:
Some AC/DC equipment was designed to be switchable to be able to operate off either 110 V AC (possibly with a voltage doubler) or 220–240 V AC or DC. Television receivers were produced which could run off 240 V AC or DC. The voltage was not high enough to power some circuits, so energy was
156:
rectifier or warranted the use of a power transformer with a conveniently high secondary voltage. Areas with 220–240 volt AC supplies could develop higher plate voltage with a simple rectifier. Transformerless power supplies were feasible for television receivers in 220–240 volt areas. Additionally,
56:
was supplied at different voltages in different places, and either direct current (DC) or alternating current (AC) was supplied. There are three ways of powering electronic equipment. AC-only equipment would rely on a transformer to provide the voltages for heater and plate circuits. AC/DC equipment
129:
or a resistive mains lead are added so that, when the mains voltage is applied across the chain, the specified heating current flows. Some types of ballast resistors were built into an envelope like a tube that was easily replaceable. With mains voltages of around 220 V, the power dissipated by the
61:
would convert AC to the direct current required for operation. When connected to a DC supply, the rectifier stage of the power supply performed no active function. DC-only equipment would only run from a DC supply and included no rectifier stage. DC is almost never used in mains power distribution
138:
AC/DC equipment did not require a transformer, and was consequently cheaper, lighter, and smaller than comparable AC equipment. This type of equipment continued to be produced long after AC became the universal standard due to its cost advantage over AC-only, and was only discontinued when vacuum
204:
In the past, 110–120 V was not high enough for higher-power tube audio and television applications, and only suitable to operate low-power radio and audio equipment such as radio receivers. Higher-powered 110–120 V audio or television equipment needed higher voltages, which were obtained using a
146:
and a filter capacitor were connected directly to the mains. If the mains power was AC, the rectifier converted it to DC. If it was DC, the rectifier effectively acted as a conductor. When operating on DC, the voltage available was reduced by the voltage drop across the rectifier. Because an AC
73:
with essentially the same circuit had different models for AC supply, DC supply, and battery operation. The introduction of AC/DC circuitry allowed a single model to be used on either AC or DC mains as a selling point, and some such models added "Universal" to their name (such sets usually had
151:
AC supply voltage would have a higher effective voltage after the rectifier stage. In areas using 110–120 volt AC, a simple half-wave rectifier limited the maximum plate voltage that could be developed; this was adequate for relatively low-power audio equipment, but television receivers or
92:
to provide a boosted HT supply; this was not possible with a lower mains supply voltage—even 220 V was insufficient. Pye's marketing material did not mention the set's ability to operate from a DC supply, possibly because there were no DC supplies within the reception range of
229:
With widespread adoption of solid-state design in the 1970s, voltage and power requirements for tabletop portable radio receivers dropped significantly. One common approach was to design a battery-powered radio (typically 6 volts DC from four
43:
that eliminated the bulky and expensive mains transformer. A side-effect of the design was that the receiver could in principle operate from a DC supply as well as an AC supply. Consequently, they were known as "AC/DC receivers".
449:
True AC/DC 240V monochrome TV. For 190–220 V AC operation needed an additional autotransformer. DC operation was possible, but was not an advertised feature; the transformerless design was to save size and
642:
This is the range from a large collection of TV servicing data. 20 volts is the ITT FS12 (12″ B&W), and 50 volts is the BRC2000 chassis used in a fair number of early transistorised 25″ colour TV sets.
593:. Philips Technical Library. p. 254-258. Ed. N.S. Markus & J. Otte. Elsevier Press. 1952 (English edition). (With ballast (barretter), detailed description and circuit diagram. Retrieved June 21, 2013.
176:
Transformerless "hot chassis" televisions continued to be commonly manufactured long after transistorisation rendered live-chassis design obsolete in radios. By the 1990s, inclusion of
105:
Vacuum tube equipment used a number of tubes, each with a heater requiring a certain amount of electrical power. In AC/DC equipment, the heaters of all the tubes are connected in
97:, then Britain's only operating transmitter. Other manufacturers adopted the design; they, and later also Pye, sold them as AC/DC sets; the technique was used for many decades.
346:
Pty, Ltd. February 22, 1952. Via KevinChant.com. Retrieved June 21, 2013. (Manual of 1952 Astor with instructions on use with AC and DC mains of different voltages)
415:. Philips Technical Library. p. 264-269. Ed. N.S. Markus & J. Otte. Elsevier Press. 1952 (English edition).(Detailed description and circuit diagram)
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waveform has a voltage peak that is higher than the average value produced by the rectifier, the same set operating on the same
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In an AC/DC design there was no transformer to isolate the equipment from the mains. Much equipment was built on a metal
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481:"Image of pye television receiver, type b18t, 1948. by Science & Society Picture Library (of Science Museum Group)"
84:
Television receivers were first commercially sold in
England in 1936 for the new 'Television Service' broadcast by the
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as TVs needed to be interconnectable with VCRs, game consoles and video disc players. The widespread replacement of
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23:
So-called "All
American Five" vacuum tube radio receivers used a power supply that could work on either AC or DC
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Classicwireless.co.uk. Anonymous. Retrieved June 21, 2013. (Offers AC/DC operation as a selling point).
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393:
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after the turn of the millennium resulted in televisions using primarily low voltages, obtained from
624:. Foulsham Technical Books / Thorn Radio Valves & Tubes Ltd. 1971. pp. 173–174. Via Archive.org.
214:
89:
40:
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118:
480:
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78:
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394:"An eight-valve 110 V AC or 220 V AC/DC superheterodyne receiver with push-pull output stage"
522:"The set is the first on the market in which this technique has been applied to television."
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113:) but at different voltages, according to their heating power requirements. If necessary,
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246:(120 V or 240 V AC, depending on region) as an alternative to battery-powered operation.
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user-settable voltage tapping arrangements to cater for the wide range of voltages).
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109:. All the tubes are rated at the same current (typically 100, 150, 300, or 450
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PAL Receiver servicing, D.J.Seal, 8, 175, pub. Foulsham & Co Ltd. 1971,
239:
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58:
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would connect all the tube heaters in series to match the supply voltage; a
231:
126:
362:
Max
Robinson. Angelfire.com. Retrieved June 21, 2013. (Third sentence.)
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561:(from National Union Radio Corp), January 1939. Via Antiqueradios.com.
19:
18:
381:. WA2ISE personal webpage. Netcom.com. Retrieved June 21, 2013.
65:
Different radio set models were required for AC, DC mains, and
85:
609:. California Historical Radio Society. Via Antiqueradios.com.
583:
Data and
Circuits of Radio Receiver and Amplifier Valves IIIa
405:
Data and
Circuits of Radio Receiver and Amplifier Valves IIIa
330:. Classicwireless.co.uk. Anonymous. Retrieved June 21, 2013.
292:. Classicwireless.co.uk. Anonymous. Retrieved June 21, 2013.
213:
recovered during the flyback period from the primary of the
196:. The potentially-hazardous "floating chassis" was no more.
139:
tubes were replaced by low-voltage solid-state electronics.
205:
step-up transformer based power supply, or sometimes an AC
152:
higher-powered amplifiers required either a more complex
372:"History of the AA5 (All American 5ive) AM tube radio"
466:Co. Retrieved June 21, 2013. (Showing AC/DC models
161:allowed multiple independent power supplies from
470:0.5.0 (about 2%) more expensive than AC only.)
77:The first ever AC/DC design of radio was the
8:
571:"VII. A five-valve receiver for AC/DC mains"
48:Applicability to early radio and television
621:The MAZDA Book of PAL Receiver Servicing
603:"Resistive Line Cords And Ballast Tubes"
389:
387:
180:input jacks required elimination of the
275:
548:"All About Ballast and Resistor Tubes"
423:
421:
7:
663:. UK. pp. 88–89. Archived from
506:"Pye B18T AC/DC Television Chassis"
429:"Pye B18T AC/DC Television Chassis"
209:, therefore operating off AC only.
95:Alexandra Palace television station
652:Burrell, Malcolm (December 1979).
14:
654:"Vintage TV: The Bush Model TV22"
283:"Murphy Radio Model A4 From 1933"
340:"Technical Bulletin: Model 'PS'"
256:
86:British Broadcasting Corporation
234:) but include a small built-in
69:operation. For example, a 1933
1:
163:separate transformer windings
677:– via domino405.co.uk.
321:"Decca 'Universal 55' radio"
52:In the early days of radio,
704:History of radio technology
720:
433:The National Valve Museum
194:switching power supplies
553:March 16, 2014, at the
485:Scienceandsociety.co.uk
356:"The All American Five"
344:Astor Radio Corporation
215:line output transformer
190:liquid crystal displays
90:line output transformer
699:Electrical engineering
588:June 29, 2011, at the
576:June 29, 2011, at the
410:June 29, 2011, at the
399:June 29, 2011, at the
165:for different stages.
24:
236:step down transformer
217:to provide a boosted
29:AC/DC receiver design
22:
271:Notes and references
41:television receivers
16:Type of power supply
633:Seal, 1971, p. 173.
618:Seal, D.J. (1971).
200:Regional variations
101:Series tube heaters
377:2017-04-24 at the
326:2016-03-03 at the
307:2020-02-17 at the
288:2020-02-17 at the
264:Electronics portal
25:
244:mains electricity
225:Transistor radios
186:cathode ray tubes
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439:. December 1948
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360:Fun with Tubes.
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309:Wayback Machine
302:"Sunbeam radio"
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672:. Retrieved
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607:CHRS Journal
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71:Murphy radio
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33:power supply
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559:Radio Craft
178:audio-video
159:transformer
134:Transformer
125:), a power
37:vacuum tube
688:Categories
674:2013-06-21
661:Television
115:resistance
242:to allow
240:rectifier
232:dry cells
144:rectifier
123:barretter
62:anymore.
59:rectifier
39:radio or
586:Archived
574:Archived
551:Archived
443:21 April
408:Archived
397:Archived
375:Archived
324:Archived
305:Archived
286:Archived
250:See also
127:resistor
580:(PDF).
516:17 July
490:19 July
450:weight.
342:(PDF).
170:chassis
67:battery
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107:series
668:(PDF)
657:(PDF)
188:with
533:ISBN
518:2016
492:2016
445:2021
238:and
35:of
27:An
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420:^
386:^
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142:A
111:mA
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