Machlett Laboratories

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Machlett Laboratories was a Northeastern United States-based company that manufactured X-ray and high-power vacuum tubes. Machlett was a large producer of the tubes and developed accessories to be used with them as well.

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For its contributions to World War II efforts, the US government gave it an "E" award in 1945. The company was bought by Varian in 1989.

History

The company began as E. Machlett and Son, which was founded in 1897 in New York City, United States as scientific glass makers.

Early days

Machlett Laboratories was created from E. Machlett & Sons in order to exploit the then new technology of X-rays. They made X-ray tubes from the beginning to 1989 when they were bought by Varian. In addition to making X-ray tubes, they manufactured high-power vacuum tubes for use in radio and TV broadcasting (857B mercury-vapor half-wave rectifier tube) and for industrial induction heating. Those two sides of the business were about equivalent for most of the life of the company.

Machlett Laboratories, Inc. was established in 1934 on Hope Street and Camp Avenue Stamford, Connecticut. This manufacturing operation began making X-ray tubes and became the largest producer of its kind in the world. Raymond was president of the company, founded by his father Robert, a scientist who made the first practical X-ray tube in America and devoted his life to making it safe and successful in the field of medicine. Robert Machlett associated with Madame Curie and other leading roentgenologists to make this happen.

They moved to 1063 Hope St. in Stamford, Connecticut, in the early 20th century, and remained there. Among their achievements was a counter made by them for Irene and Frederic Joliot-Curie for use in their experiments on artificial radioactivity in 1934 which is currently contained in the Science Museum in Great Britain. They were given an “E” award by the US government in 1945 for their contribution to the war effort. [1]

Products

Transmitting tubes

Machlett Labs 298A radio transmission tube, ca. 1958. This was the largest transmission tube made. This one is on display at the Georgia Museum of Radio History in St. Marys, GA, USA. Machlett 298A radio transmission tube.JPG
Machlett Labs 298A radio transmission tube, ca. 1958. This was the largest transmission tube made. This one is on display at the Georgia Museum of Radio History in St. Marys, GA, USA.

Machlett was well known for its rather complete line of transmitting tubes, most particularly triodes.

For quite a while, Machlett's 6697s [2] were the most-used Class B modulator tubes (as a push-pull pair) and Class C final tubes (as a single-ended pair) in 50,000-watt plate-modulated AM transmitters.

In a classical Doherty amplifier (a Class B "carrier" tube and a Class C "peak" tube), 50,000 watts could be achieved using only two 6697s, but the drive requirement was about 5,000 watts, so the driver was often a complete 5,000-watt transmitter. The driver power could be "passed through" (i.e., was not dissipated as heat) if the carrier tube was operated with a grounded grid and, as before, the peak tube was operated with a grounded cathode. [3]

Later, chief competitor Eimac released tetrodes which rather quickly eclipsed Machlett's triodes, as tetrodes have higher gain (thereby requiring much lower driver power, usually about 1,000 watts for 50,000 watts out), and do not require "neutralization". And tetrodes can be screen-grid modulated, especially in a Sainton-modified Doherty amplifier, [4] where both the "carrier" and "peak" tubes may be operated in Class C. [5]

6697s were also employed in RCA's upgraded Ampliphase transmitter, the BTA-50H.

CPI's Econco division remanufactures Eimac and Machlett power tubes.

X-ray tubes

They were the first company to utilize the concept of the rotating anode, something which is just about universal in medical X-ray systems at this date. Towards the end of the time of manufacture, they were producing oil-circulating X-ray tubes with a heat exchanger attached (for use with computed tomography (CT) scanners), with 5-inch diameter rotating anodes formed from tungsten-rhenium alloy and molybdenum, with a large mass of graphite attached to act as a heat sink. Smaller tubes without graphite heat sinks had highly radiative coatings to disperse the generated heat into the oil surrounding the tube itself.

The manufacture of X-ray tubes was licensed to two other companies, GEC Medical and Comet SA of Bern in Switzerland.

Machlett X-ray tube

The Machlett X-ray tube was produced to ‘provide electrostatic protection for the filament (cathode) so as to permit long life to be achieved at operating voltages in the range 100-300 kV’ i . The X-ray tube was designed and manufactured by E. Machlett & Son who were specialists in scientific glass instruments. The American company, which was established in New York 1897, began as a single shop and soon grew into an internationally recognized firm. The Machlett X-ray tube was patented in April 1934; one of its tubes, at the University of Melbourne's School of Physics, is from 1937. These X-ray tubes may have been used by Professor T.H Laby's X-ray group, which was a priority research topic there. This interest was sparked by the appointment in 1889 of Professor T. R. Lyle. Lyle, who was head of the school until 1915, is thought to have been the first person in Australia to have taken an X-ray photograph iii. A photocopy of this photograph can be found in the School of Physics Archive. For this particular experiment, Lyle actually made his own x-ray tube. His successor, Laby, continued to work with X-rays. During the 1920s he worked on the X-ray spectra of atoms and in 1930 he, along with Dr C. E. Eddy, published Quantitative Analysis by X-Ray Spectroscopy iv . Also with Eddy Laby produced the paper "Sensitivity of Atomic Analysis by X-rays". Laby went on to have an X-ray spectrograph of his own design manufactured by Adam Hilger Ltd.

Accessories

As well as X-ray tubes, they manufactured collimators – to define the beam size – and three marks of “Dynalyser” – an invasive instrument for measuring all the important parameters in an X-ray tube. This consisted of an HV unit insulated with SF6, and an indicating unit. A separate radiation monitor could be used with this, and an oscilloscope could also be attached to this device if desired. Some 2,500 of the most recent version were sold, and this device survived the sale of the company to Varian and later buyers, being in production from the early 1980s to around 1995.

There were three generations of the Dynalyzer produced. Maintenance on the Dynalyzer is available by its inventor, Dr. Jon Shapiro, at http://giciman.com

Related Research Articles

<span class="mw-page-title-main">Triode</span> Single-grid amplifying vacuum tube having three active electrodes

A triode is an electronic amplifying vacuum tube consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode). Developed from Lee De Forest's 1906 Audion, a partial vacuum tube that added a grid electrode to the thermionic diode, the triode was the first practical electronic amplifier and the ancestor of other types of vacuum tubes such as the tetrode and pentode. Its invention founded the electronics age, making possible amplified radio technology and long-distance telephony. Triodes were widely used in consumer electronics devices such as radios and televisions until the 1970s, when transistors replaced them. Today, their main remaining use is in high-power RF amplifiers in radio transmitters and industrial RF heating devices. In recent years there has been a resurgence in demand for low power triodes due to renewed interest in tube-type audio systems by audiophiles who prefer the pleasantly (warm) distorted sound of tube-based electronics.

<span class="mw-page-title-main">Vacuum tube</span> Device that controls electric current between electrodes in an evacuated container

A vacuum tube, electron tube, valve, or tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.

A tetrode is a vacuum tube having four active electrodes. The four electrodes in order from the centre are: a thermionic cathode, first and second grids and a plate. There are several varieties of tetrodes, the most common being the screen-grid tube and the beam tetrode. In screen-grid tubes and beam tetrodes, the first grid is the control grid and the second grid is the screen grid. In other tetrodes one of the grids is a control grid, while the other may have a variety of functions.

<span class="mw-page-title-main">Valve amplifier</span> Type of electronic amplifier

A valve amplifier or tube amplifier is a type of electronic amplifier that uses vacuum tubes to increase the amplitude or power of a signal. Low to medium power valve amplifiers for frequencies below the microwaves were largely replaced by solid state amplifiers in the 1960s and 1970s. Valve amplifiers can be used for applications such as guitar amplifiers, satellite transponders such as DirecTV and GPS, high quality stereo amplifiers, military applications and very high power radio and UHF television transmitters.

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<span class="mw-page-title-main">6L6</span> Vacuum tube

6L6 is the designator for a beam power tube introduced by Radio Corporation of America in April 1936 and marketed for application as a power amplifier for audio frequencies. The 6L6 is a beam tetrode that utilizes formation of a low potential space charge region between the anode and screen grid to return anode secondary emission electrons to the anode and offers significant performance improvements over power pentodes. The 6L6 was the first successful beam power tube marketed. In the 21st century, variants of the 6L6 are manufactured and used in some high fidelity audio amplifiers and musical instrument amplifiers.

<span class="mw-page-title-main">Beam tetrode</span>

A beam tetrode, sometimes called a beam power tube, is a type of vacuum tube or thermionic valve that has two grids and forms the electron stream from the cathode into multiple partially collimated beams to produce a low potential space charge region between the anode and screen grid to return anode secondary emission electrons to the anode when the anode potential is less than that of the screen grid. Beam tetrodes are usually used for power amplification, from audio frequency to radio frequency. The beam tetrode produces greater output power than a triode or pentode with the same anode supply voltage. The first beam tetrode marketed was the Marconi N40, introduced in 1935. Beam tetrodes manufactured and used in the 21st century include the 4CX250B, KT66 and variants of the 6L6.

<span class="mw-page-title-main">Pentode</span> Vacuum tube with five electrodes

A pentode is an electronic device having five electrodes. The term most commonly applies to a three-grid amplifying vacuum tube or thermionic valve that was invented by Gilles Holst and Bernhard D.H. Tellegen in 1926. The pentode was developed from the screen-grid tube or shield-grid tube by the addition of a grid between the screen grid and the plate. The screen-grid tube was limited in performance as an amplifier due to secondary emission of electrons from the plate. The additional grid is called the suppressor grid. The suppressor grid is usually operated at or near the potential of the cathode and prevents secondary emission electrons from the plate from reaching the screen grid. The addition of the suppressor grid permits much greater output signal amplitude to be obtained from the plate of the pentode in amplifier operation than from the plate of the screen-grid tube at the same plate supply voltage. Pentodes were widely manufactured and used in electronic equipment until the 1960s to 1970s, during which time transistors replaced tubes in new designs. During the first quarter of the 21st century, a few pentode tubes have been in production for high power radio frequency applications, musical instrument amplifiers, home audio and niche markets.

<span class="mw-page-title-main">Single-ended triode</span> Vacuum tube electronic amplifier that uses a single triode to produce an output

A single-ended triode (SET) is a vacuum tube electronic amplifier that uses a single triode to produce an output, in contrast to a push-pull amplifier which uses a pair of devices with antiphase inputs to generate an output with the wanted signals added and the distortion components subtracted. Single-ended amplifiers normally operate in Class A; push-pull amplifiers can also operate in Classes AB or B without excessive net distortion, due to cancellation.

Eimac is a trade mark of Eimac Products, part of the Microwave Power Products Division of Communications & Power Industries. It produces power vacuum tubes for radio frequency applications such as broadcast and radar transmitters. The company name is an initialism from the names of the founders, William Eitel and Jack McCullough.

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The KT88 is a beam tetrode/kinkless tetrode vacuum tube for audio amplification.

<span class="mw-page-title-main">Valve RF amplifier</span> Device for electrically amplifying the power of an electrical radio frequency signal

A valve RF amplifier or tube amplifier (U.S.) is a device for electrically amplifying the power of an electrical radio frequency signal.

Technical specifications and detailed information on the valve audio amplifier, including its development history.

In the years 1942-1944, the Radio Manufacturers Association used a descriptive nomenclature system for industrial, transmitting, and special-purpose vacuum tubes. The numbering scheme was distinct from both the numbering schemes used for standard receiving tubes, and the existing transmitting tube numbering systems used previously, such as the "800 series" numbers originated by RCA and adopted by many others.

<span class="mw-page-title-main">4-1000A</span>

The 4-1000A/8166 is a radial-beam tetrode designed for use in radio transmitters. The 4-1000A is the largest of a series of tubes including the 4-65A, 4-125A, 4-250A, and the 4-400A. These tubes share a common naming convention in which the first number identifies the number of elements contained within the tube; i.e., the number “4” identifies the tube as a tetrode which contains four elements, and the second number indicates the maximum continuous power dissipation of the anode in Watts. The entire family of tubes can be used as oscillators, modulators, and amplifiers.

<span class="mw-page-title-main">8974</span>

8974 / X-2159 is a power tetrode designed for megawatt power levels in industrial and broadcast applications.

<span class="mw-page-title-main">807 (vacuum tube)</span>

The 807 is a beam tetrode vacuum tube, widely used in audio- and radio-frequency power amplifier applications.

The Doherty amplifier is a modified class B radio frequency amplifier invented by William H. Doherty of Bell Telephone Laboratories Inc in 1936. Whereas conventional class B amplifiers can clip on high input-signal levels, the Doherty power amplifier can accommodate signals with high peak-to-average power ratios by using two amplifier circuits within the one overall amplifier to accommodate the different signal levels. In this way, the amplifier achieves a high level of linearity while retaining good power efficiency.

References

  1. ↑ no longer at 1063 Hope St.
  2. ↑ "ML-6697A datasheet & application notes - Datasheet Archive".
  3. ↑ Continental Electronics 317B
  4. ↑ USpatent 3314024,Joseph B. Sainton,"High Efficiency Amplifier and Push–Pull Modulator",issued 1967-04-11, assigned to Continental Electronics Manufacturing Company
  5. ↑ Continental Electronics 317C
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