Variac V20
Date: 1940-1950
Inventory Number: 2004-1-0182
Classification: Transformer
Subject:
Maker: General Radio Company (1915-present)
User: Edwin H. Land (1909 - 1991)
Cultural Region:
Place of Origin:
Dimensions:
17 x 22 x 24 cm (6 11/16 x 8 11/16 x 9 7/16 in.)
Bibliography:
Operating Instructions V-20 Series Variac
Description:
This is a variable autotransformer used for power supply testing. The name Variac comes from "Variable AC". Look at the pdf file attached for all the technical details on this instrument.
In Collection(s)
Signedon instrument: GENERAL RADIO COMPANY, CAMBRIDGE, MASS. U.S.A.
on dial: GR
between numerals: VARIAC
molded on stem: VARIAC
on dial: GR
between numerals: VARIAC
molded on stem: VARIAC
FunctionThe Variac adjustable transformer was introduced by General Radio in 1933. ("Variac" is short for variable AC.) It is an inductor, featuring a copper winding wrapped around a steel core. It is a tool used to attain a desired voltage (anywhere from 0 to 140 Volts). Its major use is to test equipment in order to see what range of voltage that equipment is capable of handling.
Curatorial RemarksThis instrument's patent is dated 23 July 1935. The introduction reads thusly: "The present invention relates principally to alternating-current apparatus, such as transformers and choke coils, and particularly to apparatus of this kind in which a movable contact means, such as a contact member, is employed to vary either the voltage or the usable portion of a winding. The invention also relates to arrangements for making successive connections to a series of points at dirrerent electrical potentials without interrupting the circuit.
It has heretofore been proposed to provide apparatus of the above-described character, in which no resistance is introduced in the contact member. Such apparatus is either wholly inoperative or, if operative at all, can work only with a low-voltage winding; and then only a low efficiency. Otherwise, there would be liability of excessive short-circuit current, resulting in damage to the transformer."
[see online patent number 2,009,013 at the U.S. Patent Office here.]
It has heretofore been proposed to provide apparatus of the above-described character, in which no resistance is introduced in the contact member. Such apparatus is either wholly inoperative or, if operative at all, can work only with a low-voltage winding; and then only a low efficiency. Otherwise, there would be liability of excessive short-circuit current, resulting in damage to the transformer."
[see online patent number 2,009,013 at the U.S. Patent Office here.]
Primary SourcesGeneral Radio Co., Operating Instructions V-20 Series Variac (Cambridge, MA: General Radio Co., ca 1940).
ProvenanceThis object belonged to Edwin H. Land and came from the Rowland Institute, Harvard University. Gift of the Edwin H. Land Family.