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Docket #:2017-15

This Proposal has been approved, and is now a Milestone

To the proposer’s knowledge, is this achievement subject to litigation? No

Is the achievement you are proposing more than 25 years old? Yes

Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes

Did the achievement provide a meaningful benefit for humanity? Yes

Was it of at least regional importance? Yes

Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? Yes

Has an IEEE Organizational Unit agreed to arrange the dedication ceremony? Yes

Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes

Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes

Year or range of years in which the achievement occurred:


Title of the proposed milestone:

The Silicon Controlled Rectifier (SCR)/Thyristor 1957

Plaque citation summarizing the achievement and its significance:

The three-terminal p-n-p-n device introduced by General Electric (GE) in 1957 as the silicon controlled recifier (SCR, later thyristor)became the dominant control device in the power industry. The development of the SCR revolutionized the control of electrical machines. Prior to 1955, triode vacuum tubes were used fro machine control that were difficult to operate and were notoriously unreliable. The symmetrical switch (TRIAC) evolved from the SCR, later still came the gate turn-turn-off thyristor.

In what IEEE section(s) does it reside?

Schenectady, New York

IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Unit: Power Electronics Society
Senior Officer Name: Alan Mantooth, President

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: Power Electronics Society
Senior Officer Name: Alan Mantooth, President

IEEE section(s) monitoring the plaque(s):

IEEE Section: Schenectady, New York
IEEE Section Chair name: Amal Mallavarapu

Milestone proposer(s):

Proposer name: W.G. Hurley
Proposer email: Proposer's email masked to public

Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.

Street address(es) and GPS coordinates of the intended milestone plaque site(s):

Museum of Science and Innovation 15 Nott Terrace Heights Schenectady, NY 12308 U.S.A.

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. The Museum of Science and Innovation has custody of the GE Heritage Museum

The General Electric Photograph collection consists of nearly 1.5 million images dating from 1891-1960 and depicts the development of the electrical industry and 20th century American life. The images document almost every aspect of the company, including product installations, advertising, consumer and industrial products, factories, executives, researchers, and factory workers

Are the original buildings extant?

The original buildings where the SCR was developed is no longer there.

Details of the plaque mounting:

In the lobby of the Museum

How is the site protected/secured, and in what ways is it accessible to the public?

The Plaque will be visible to the public in the lobby of the Museum. There will be an exhibition of materials related to the SCR/Thyristor in the Museum itself

Who is the present owner of the site(s)?

Museum of Science and Innovation,   Schenectady

What is the historical significance of the work (its technological, scientific, or social importance)?

The invention of the SCR/Thyristor revolutionized the control of power conversion by replacing vacuum tube mercury-arc controlled rectifirer (the thyratron) with a three terminal semiconductor device. It is a four layer three terminal solid state semiconductor device. It has an anode, a cathode and a gate. The diode is a two terminal device, current flows from the anode to the cathode when a positive voltage is applied betweent the anode and the cathode. The SCR operates like a diode except that current cannot flow until a small voltage is applied between the gate and the cathode. Current flow is stopped by reducing the current below the latching value. The first application for the SCR was in the area of phase controlled rectification that allowed ac voltage to be converted to dc voltage and by delaying the trigger point the average value of the dc output can be regulated.

What obstacles (technical, political, geographic) needed to be overcome?

What features set this work apart from similar achievements?

Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.

Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to Please see the Milestone Program Guidelines for more information.

Please email a jpeg or PDF a letter in English, or with English translation, from the site owner(s) giving permission to place IEEE milestone plaque on the property, and a letter (or forwarded email) from the appropriate Section Chair supporting the Milestone application to with the subject line "Attention: Milestone Administrator." Note that there are multiple texts of the letter depending on whether an IEEE organizational unit other than the section will be paying for the plaque(s).