DUMONT TELESET MODEL MANSFIELD YEAR 1960.

 

The DUMONT TELESET MODEL MANSFIELD is a20 inches B/W television with VHF and (after added) UHF tuners.

Tuning is obtained with rotatable drum selectors for VHF and variable rotatable capacitor for UHF.
A rotatable drum containing twelve pre-defined channel-specific filters determines the received channel, where the inductors of the input matching, the channel filter and the LO tank circuit are changed. The tuner is divided into two chambers for maximum isolation between the sensitive RF input and the mixer-oscillator-IF section with its much larger signals. Also on the drum there are eventually two separate sub-modules.
It's completely based on tubes technology.
With this concept, which essentially turned the tuner module into a kind of Lego building block construction, many different tuners became possible. Depending upon the country of destination and its associated standard and IF settings, the required filter modules would be selected. Service workshops and tv fabricants could later even add or exchange modules when new channels were introduced, since every inductor module had its individual factory code and could be ordered separately. As a consequence more versions of the tuner were produced, covering at least standards B, B-for-Italy, C. E, F and M.


The principle of the drum tuner. On an axis two times 12 regularly spaced channel-specific filter modules are mounted. In front are twelve channel filter modules for both the channel filter and LO tank circuit tuning. Seven contacts are available, and one module is shown removed. The second row contains 12 modules with five contacts for the input filter circuit. In the tuner module the front section (for mixer-ocillator and channel filter) is separated by a metal shield from the rear RF input and pre-amp section. [Philips Service "Documentatie voor de kanalenkiezers met spoelenwals", 1954]

Examples of the filter modules as used in the drum tuner. Left the 5-contact input filter, right the 7-contact BPF and LO tank filters. In both modules the coils are co-axial for (maximum) mutual coupling.





The second new valve introduced in the tuners family was the PCF80, a triode-pentode combo valve specifically designed for the VHF mixer-oscillator role. First order the circuit principles didn't change too much from the previous ECC81 based generation, with the triode acting as a Colpitts oscillator with a tuned feedback from anode to grid. The oscillator voltage was minimally 5V at the grid, and would be inductively coupled to the input of the mixer pentode. This inductive coupling was achieved by putting the oscillator coil S7 and the BPF coils S5 and S6 on the same rod inside the drum tuner filter modules, see Fig.5 above. By adjusting the distance between these coils for each channel filter module, the coupling constant could be kept more or less constant across all channels, providing as much as possible a frequency-independent mixer performance. For the mixer the pentode replaced the previous triode, providing more feedback isolation between anode and grid. All in all the new tuner must have given a considerable performance improvement compared to the previous generation.


Frontly a heavy glass is present and the set is really heavy.

The rear cover lid is a full steel panel with paper panel and all directly grounded chassis mains live !!!!

A voltage changer is present but the set is originally powered at 125volt.

Completely based on tubes technology even in power supply.

(NOTE knobs aren't originals)

The set is last DUMONT set fabricated before closing his activity in 1960.


The B/W Tubes Television set was powered with a External Voltage stabiliser unit (portable metal box) which relates to voltage regulators of the type employed to supply alternating current and a constant voltage to a load circuit from a source in which the line voltage varies.Conventional AC-operated television receivers exhibit several undesirable performance attributes. For example, under low-line voltage conditions such as those encountered during peak load periods or temporary power brown-outs imposed during times of power shortage, picture shrinkage and defocusing are encountered and under extreme brown-out conditions the receiver loses synchronization with a resultant total loss of picture intelligibility.

On the other hand, abnormally high-line voltage conditions are sometimes encountered, and this can lead to excessive high voltage and X-ray generation. In addition, either abnormally high steady state line voltage conditions or high voltage transients such as those encountered during electrical storms or during power line switching operations may subject the active devices and other components of the receiver to over-voltage stresses which can lead to excessive component failure.

It is a principal object of the present invention to provide a new and improved AC-operated television receiver having greatly improved performance characteristics in the presence of fluctuating power supply voltages.

A more specific object of the invention is to provide an AC-operated television receiver affording substantially undegraded performance under even extremely low-line voltage conditions without excessive high voltage and X-ray generation under even extremely high-line voltage conditions.

Still another and extremely important object of the invention is to provide a new and improved AC-operated television receiver having greatly improved reliability against component failure. Such regulators are frequently provided employing saturable core reactors and condensers connected in circuit...  in such manner as to provide a plurality of variable voltage vectors which vary in different senses, as the line voltage varies, but which add vectorially in such manner that their vector sum remains substantially constant upon variations in line voltage, for providing automatic voltage stabilization of single or multiphase A. C. circuits where the supply voltage and frequency are subject to variation above and below normal value and where the load is subject to variation between normal limits.
voltage stabilization
is automatically effected by the provision of an inductive pilot control device which is adapted to provide two excitation supply voltages for producing excitation or satuation of two magnetic circuits of a reversible booster transformer unit or units and diversion of flux from one magnetic circuit to the other, the booster unit being energized by primary windings from the A. C. supplysystem and being provided with a secondary winding or windings connected between the supply system and the corresponding inain or distribution circuit and in series therewith, through which a corrective boost voltage is
imrorjiiced into the circuit under the influence of the pilot control device, of an amount equal to that of the supply voltage fluctuation which initiated it and appropriate in polarity and direction for restoring the voltage to normal value and providing automatic stabilization of the circuit voltage against supply voltages which fluctuate above and below normal value.

The pilot control device which may be employed singly or may comprise three units or their equivalent when applied to multiphase supply systems comprises a pair of closed magnetic circuits or cores constructed of strip wound magnetic material or stacked laminations, the two
circuits forming a pair being constructed of materials possessing dis~similar magnetic characteristics when jointly energized by identical windings in series or by a collective primary winding, the said magnetic circuits being suitably proportioned to provide equal fluxes when ener-
gized at normal voltage.

The pilot control device is provided with a main and an auxiliary secondary winding or group of windings, the main secondary winding or windings being adapted to provide a voltage representing the difference in the fluxes of the two circuits to which it is jointly associated, while
the auxiliary secondary winding embraces only one circuit, preferably that subject to the least amount of flux variation. Either of the windings consists of two equal sections or in effect a double winding with a center tapping to which one end of the single winding is connected.

The voltage in the single secondary winding of the pilot device becomes directionally additive to that in one half of the tapped secondary winding and substractive in respect to that in the other half. When the supply voltage is normal the voltage provided by the single secondary winding is zero, since there is no difference of flux in the two magnetic circuits, and the two excitation voltages
produced in the halves of the other secondary winding are equal and when connected to the two excitation windings of the booster units, do not produce any diversion of flux between the two circuits or sets of circuits in the magnetic system of the booster transformer unit become equal, and since the series winding on the booster unit is arranged to provide a voltage due to the difference of
the fluxes in its two magnetic circuits or sets of magnetic circuits, no corrective voltage is introduced into the main circuit by the booster. If, however, the supply voltage varies from normal the pilot control device provides a voltage across the one secondary winding due to the difference in the fluxes of the two dis-similar magnetic circuits of which it is comprised, which voltage is combined with thosc in the halves of the other secondary winding to provide two excitation voltages which vary complementarily to each other as the supply voltage fluotuates, and cause a transference of flux between the two
circuits or groups of circuits in the booster unit and automatically provide a corrective boost voltage in the main circuit in which the series winding of the booster transformer is includcd of a value equal to that of the variation in supply voltage which initiated it.
The pilot device may be arranged in various ways, forboth single phase and multiphase operation, as exemplified by the constructions hereinafter more fully described.Similarly, numerous arrangements of the booster transformer unit are possible, some of which are hereinafter described in detail. The booster transformer unit embodies thc principles of the inductive devices described in my co-pending Application No. 411,189, filed February 18, 1954.

As an alternative to the provision of an auxiliary secondary winding on the pilot control device this may be
replaced by an independent or external source of supply,which may be either subject to or independent of supply voltage variation, provided such supply may be arranged with a center tapping if required.

Feed-back arrangements may be employed for providing compensation against voltage drop due to the effects of load in various ways. These are preferably providedon the booster transformer unit and may comprise a current transformer in one or more lines of the main circuit,
the secondary output of the transformer being rectified and arranged to energize an additional excitation winding on the booster transformer unit which in clfect increases the amount of the corrective boost voltage as the load increases.

A good point  about  B/W Televisions.....................

The Sixties was a time of great change for TV. At the start of the decade there were just monochrome sets with valves, designed for 405 -line transmissions at VHF. By the end there was 625 -line colour at UHF, with transistorised chassis that used the odd IC.

The following decade was one of growth. The "space race" had begun in 1957, when the USSR launched Sputnik 1 and terrified the Americans. Thereafter the USA began to spend countless billions of dollars on space missions. This got underway in earnest in the Sixties, with the announcement that America would be going all out to get a man on the moon by the end of the decade. There followed the Mercury series of earth - orbit missions, then the Apollo launches. Success was achieved in 1969. Most of these missions were televised, and in those days anything to do with space was hot stuff. It was inevitable that everyone wanted to have a television set. At the time an average receiver would be a monochrome one with a 14in. tube - there was no colour until 1967. It would cost about 75 guineas. 
TV sets were often priced in guineas (21 shillings) as it made the price look a bit easier on the pocket. Anyway 75 guineas, equivalent to about £78.75 in 2000's currency, was a lot of money then.  For those who couldn't, rental was a good option. The Sixties was a period of tremendous growth for rental TV. 
Much else was rented at that time, even radios, also washing machines, spin driers, refrigerators and, later on, audio tape recorders (no VCRs then). 
For most people these things were too expensive for cash purchase. 
There were no credit cards then. And when it came to a TV set, the question of reli- ability had to be taken into account: renting took care of repair costs. 

TV reliability.........The TV sets of the period were notoriously unreliable. They still used valves, which meant that a large amount of heat was generated. The dropper resistor contributed to this: it was used mainly as a series device to reduce the mains voltage to the level required to power the valve heaters. These were generally connected in series, so the heater volt- ages of all the valves were added together and the total was subtracted from the mains voltage. The difference was the voltage across the heater section of the dropper resistor, whose value was determined by simple application of Ohm's Law. 
As valves are voltage -operated devices, there was no need to stabilise the current. So the power supply circuits in TV sets were very simple. They often consisted of nothing more than a dropper resistor, a half or biphase rectifier and a couple of smoothing capacitors. If a TV set had a transformer and a full wave rectifier in addition to the other components, it was sophisticated!
 As the valve heaters were connected in series they were like Christmas -tree lights: should one fail they all went out and the TV set ceased to function. Another common problem with valves is the cathode -to -heater short. When this fault occurs in a valve, some of the heaters in the chain would go out and some would stay on. Those that stayed on would glow like search- lights, often becoming damaged as a result. Dropper failure could cause loss of HT (dead set with the heaters glowing), or no heater supply with HT present. When the HT rectifier valve went low emission, there was low EHT, a small picture and poor performance all round. CRTs would go soft or low emission, the result being a faint picture, or cathode -to -heater short-circuit, the result this time being uncontrollable brightness. On average a TV set would have twelve to fourteen valves, any one of which could go low -emission or fail in some other way. All valves have a finite life, so each one would probably have to be replaced at one time or another. The amount of heat generated in an average TV set would dry out the capacitors, which then failed. So you can see why people rented! 

The CRT could cause various problems. Because of its cost, it was the gen- eral practice to place its heater at the earthy end of the chain. In this position it was less likely to be overloaded by a heater chain fault. But during the winter months, when the mains voltage dropped a bit, it would be starved of power. This would eventually lead to 'cathode poi- soning' with loss of emission. The 'cure' for this was to fit a booster transformer designed to overrun the heater by 10, 20 or 30 per cent. It would work fine for a while, until the CRT completely expired. At about this time CRT reactivators came into being - and a weird and wonderful collection of devices they turned out to be. Regunned tubes also started to appear. You couldn't do this with the `hard -glass' triode tubes made by Emitron. These were fitted in a number of older sets. Yes, they were still around, at least during the early Sixties.



Developments................... A great deal of development occurred during the Sixties. Many TV sets and radios made in the early Sixties were still hard -wired: the introduction of the printed circuit board changed the construction of electronic equipment forever. The first one was in a Pam transistor radio. PCBs were ideal for use in transistor radios, because of the small size of the components used and the fact that such radios ran almost cold. 
They were not so good for use with valve circuitry, as the heat from the valves caused all sorts of problems. Print cracks could develop if a board became warped. If it became carbonised there could be serious leakage and tracking problems. In addition it was more difficult to remove components from a PCB. Many technicians at that time didn't like PCBs. As the Sixties progressed, transistors took over more and more in TV sets. They first appeared in a rather random fashion, for example in the sync separator stages in some Pye models. Then the IF strip became transistorised. Early transistors were based on the use of germanium, which was far from ideal. 

The change to silicon produced devices that were more robust and had a better signal-to-noise ratio. 
Car radios became fully transistorised, and 'solid-state' circuitry ceased to be based on earlier valve arrangements. Many hi-fi amplifiers had been transistorised from the late Fifties, and all tape recorders were now solid-state. 
Both reel-to-reel and compact -cassette recorders were available at this time. Initially, audio cassette recorders had a maximum upper frequency response of only about 9kHz. 
To increase it meant either a smaller head gap or a faster speed. Philips, which developed the compact audio cassette and holds the patents for the design (which we still use in 2000!) wouldn't allow an increase in speed. Good reel-to-reel recorders had a fre- quency response that extended to 20kHz when the tape speed was 15in./sec. 
This is true hi-fi. In time the frequency response of compact -cassette recorders did improve, because of the use of better head materials with a smaller gap. 
This led to the demise of the reel-to-reel audio recorder as a domestic product We began to benefit from spin-offs of the space race between the USA and the USSR. 
The need to squeeze as much technology as possible into the early computers in the Mercury space capsules used by the USA lead to the first inte- grated circuits. 
This technology soon found its way into consumer equipment. Often these devices were hybrid encap- sulations rather than true chips, but they did improve reliability and saved space. The few chips around in those days were analogue devices.  To start with most UHF tuners used valves such as the PC86 and PC88. They were all manually tuned. Some had slow-motion drives and others had push -buttons. They didn't have a lot of gain, so it was important to have an adequate erial and use low -loss cable..............................

History:DuMont Labs, Allen B., Inc. (USA)


Founded: 1931
Closed: 1960
Radioproduction: 1938 - 1958

Allen B. DuMont supervised electron tube production for Westinghouse starting in 1924. In 1931 he founded his own company in Montclair, NJ. In 1932 he invented the "Magic Eye" cathode ray tube, and sold the rights to RCA. In 1933 he invented an early form of radar, which he was asked to keep secret (not patent) by the U.S. military. In 1934, DuMont Labs moved to Passaic, NJ. DuMont sold the first all-electronic TV (Model 180) in the U.S. in 1938. DuMont was an influential member of the National Television Standards Committee (NTSC). In 1946, the DuMont TV Network was established, with stations WABD (New York) and WTTG (Washington D.C.). The DuMont Network eventually grew to 200 stations and was sold to Metromedia in 1956. DuMont Labs produced high quality (and expensive) TVs until 1958, when the consumer products business was sold to Emerson. Notable models include the "Royal Sovereign" with its 30-inch CRT. DuMont's cathode ray tube division was sold to Fairchild Camera and Instrument in 1960 to become the A. B. DuMont Division of Fairchild, which developed the Sony Trinitron CRT under contract.



Foundation of Allen B. DuMont Laboratories, Inc.

- In 1931, Allen B. DuMont founded Allen B. DuMont Laboratories, Inc., in his garage with $1000-half of it borrowed. The company achieved its initial success as the primary U.S. manufacturer of cathode-ray tubes, which had become critical to the electronics industry. DuMont entered into television broadcasting---first experimentally, then as a commercial venture-in 1938. In fact, the only way to receive NBC-RCA's historic public broadcast of television outside their 1939 World's Fair pavilion was on sets made by DuMont Labs.

DuMont first became involved in broadcasting by building a radio transmitter and transmitter and receiver out of an oatmeal box while suffering from polio. In 1924, he received an electrical engeneering degree from Rensselaer Polytechnical Institute. After graduation, he joined the Westinghouse Lamp Company as an engineer at a time when 500 tubes a day were being produced. Later DuMont became supervisor and initiated technical improvements that increased production to 5,000 tubes per hour. In 1928, he worked closely with Dr. Lee DeForest on expanding radio, but left later to explore television.

DuMont achieved a number of firsts in commercial television practice, but with little success. He tried to expand his network too rapidly both in the number of affiliates and the number of hours of programming available to affiliates each week. Even as DuMont was developing into the first commercial television network, the other networks, most notably CBS and NBC, were preparing for the time when rapid network expansion was most feasible-experimenting with various program formats and talent borrowed from their radio networks, as well as encouraging their most prestigious and financially successful radio affiliates to apply for television licenses.

Prime-time programming was a major problem for DuMont. The network would not or could not pay for expensive shows that would deliver large audiences, thereby attracting powerful sponsors. When a quality show drew a large audience in spite of its budget, it was snatched by CBS or NBC. DuMont televised the occasional successful show, including Cavalcade of Stars (before Jackie Gleason left), Captain Video, and Bishop Fulton J. Sheen's Life Is Worth Living. The network never seemed to generate enough popular programming to keep it afloat, however-possibly be- cause it lacked the backing of a radio network.

The NBC, CBS and ABC radio networks provided financial support for their television ventures while the fledgling industry was growing-creating what the FCC deemed 'an ironic situation in which one communications medium financed the development of its competitor." DuMont's only outside financial assistance came from Paramount Studios between 1938 and 1941. The company created and sold class-B common stock exclusively to Paramount for one dollar per share and a promise to provide affiliation with CBS and NBC. Analysts have suggested that DuMont's lack of primary affiliates was a key factor in the network's demise.

One important factor contributing to the demise of the DuMont Network was Allen B. DuMont himself. Many people thought of him as a "bypassed pioneer" with no head for business. Major stockholders began to publicly question the soundness of his decisions, especially his desire to keep the TV network afloat despite major losses. In 1955, concerned holders of large blocks of DuMont stock began to wrest control from the company founder.

When the fiscally weakened DuMont corporation spun off its television broadcasting facilities in 1955, Business Week claimed that DuMont had been forced into television programming in order to provide a market for his TV receivers. No evidence has been found to support this claim, however. In markets where licenses for television stations were being granted during the postwar period, there were sufficient license applicants to provide audiences with programming to stimulate set sales. One reason DuMont television sales lagged behind other manufactures was that his sets were of higher quality, and consequently much more expensive. In fact, in 1951 DuMont cut back television set production by 60%-although profits from this division had been subsidizing the TV network-because other manufactures were undercutting DuMont's prices.

After the DuMont Television Network and its owned- and-operated stations were spun off into a new corporation, there remained only two major divisions of Allen B. DuMont Laboratories, Inc. In 1958 Emerson Electric Company purchased the DuMont consumer products manufacturing division. DuMont was no longer employed by his own company when the last division-oscillograph and cathode-ray tube manufacturing--was sold to Fairchild in 1960. DuMont was hired by Fairchild as group general manager of the A. B. DuMont Division of Fairchild Camera and Instrument Corporation until his death in 1965.

DuMont may have remained in television broadcasting despite fiscal losses in order to uphold the title once given him, 'the father of commercial television."

His company pioneered many important elements necessary to the growth and evolution of the industry. DuMont engineers perfected the use of cathode-ray tubes as TV screens, developed the kinescope process, as well as the "magic eye cathode-ray radio tuning indicator, and the first electronic viewfinder. DuMont was an intelligent and energetic engineer who took risks and profited financially from them-becoming history's first television millionaire. But when the big radio networks entered the field of television, DuMont was unable to compete with these financially powerful, considerably experienced broadcaster.

Allen B(alcom) DuMont Born in Brooklyn, New York, U.S.A., 29 January 1901. Educated at Rensselaer Polytechnic Institute, Troy, New York, B.S. in electrical engineering 1924. Married: Ethel; children: Allen B.,Jr., and Yvonne. Began career with the Westinghouse Lamp Company; conducted TV experiments in his garage,
1920s; developed an inexpensive cathode- ray tube that would last for thousands of hours (unlike the popular German import CRT, which lasted only 25 to 30 hours), DeForest Radio Company,
1930; left to found his laboratory,

1931; incorporated DuMont Labs,
1935; sold a half-interest to Paramount Pictures Corporation to raise capital for broadcasting stations, 1938; DuMont Labs was first company to market home television receiver,
1939; granted experimental TV licenses in Passaic, New Jersey, and New York,
1942; DuMont TV Network separated from DuMont Labs, sold to the Metropolitan Broadcasting Company; Emerson Radio and Phonograph Corp. purchased DuMont's television, phonograph, and stereo producing division; remaining DuMont interests merged with the Fairchild Camera and Instrument Corp.,

1960; named group general manager of DuMont divisions of Fairchild,
1960; named senior technical consultant,
1961. Honorary doctorates: Rensselaer and Brooklyn Polytechnic Institutes. Recipient: Marconi Memorial Medal for Achievement,
1945; American Television Society,

1943; several trophies for accuracy in navigation and calculations in power-boat racing.

Died in Montclair, New Jersey, 16 November 1965.

See also

• Metromedia
• Passaic: Birthplace of Television and the DuMont Story

References

Weinstein, David (2009). The Forgotten Network: DuMont and the Birth of American Television. Temple University Press. ISBN 9781592134991.

Adams, Edie (March 1996). "Television/Video Preservation Study: Los Angeles Public Hearing". National Film Preservation Board. Library of Congress.

http://www.trademarkia.com/dumont-85601209.html

External links

• Dumont Experimental Color CRTs at the Early Television Museum
• DuMont television receiver photo at Greater Boston, June 2005 gallery of broadcasting equipment. Also available is Description and index of entire gallery.