The Telegraph Office

An Unusual Spark Key From Long Time Test

Instrument Maker General Radio

c. 1916

by Neal McEwen, K5RW

Copyright © 2000, 2002, Neal McEwen

To Telegraph Office Main Page

Many of us have seen or used General Radio test instruments through the years.  I never really thought much about the history of General Radio and had no idea that the company ever made wireless components,... until I ran across this key. General Radio Key

Not only was I surprised to find a key by General Radio, but I was surprised at the design of this key.  Notice the asymmetric design. The lever is situated far to the left of the center line of the base.  Also notice that the contacts are not under the axis of the lever; they are offset to the right of the lever.  All other key designs are symmetric.  The U.S. Signal Corp. J-3 is the only exception I know of and it was designed to fit in an enclosure with other apparatus.

This key does not have a typical trunion assembly.  The lever pivots about a steel pin in a brass clevis.  Perhaps this was a way of reducing the number of parts; trunion screws and lock nuts are not needed.  The dimensions of the base are 4" by 2 5/8". This is rather small for a wireless key and is only slightly larger than the Bunnell "Standard Wireless Key."  Inscribed in the base of the key is "General Radio Co., Cambridge Mass."

Notice the cooling fins on the upper and lower contacts.  This is an indication that the key was used in high current applications and thus identifies it as a spark era key.  Spark keys were typically placed in series with the primary winding of the high voltage transformer.  The fins dissipated the heat generated by the current passing through the contacts.  The size of the contacts and the presence of the fins suggest this key would have handled 10 amps or more.

Notice the wire running from the back of the key to the top contact. On most spark keys this is a current shunt to redirect the current through the wire and around any moving parts of the trunion assembly.  However, on this General Radio key, the wire serves a different function.  The upper contact is isolated from the lever with bakelite washers, so it must be connected to the binding post via the wire, rather than through the clevis.

With the upper contact isolated, the lever has no voltage on it.  The operator is protected and will not get 'bit' should his fingers come into contact with the lever as is the case with the typical spark key.  The knob does not require a skirt to protect the operators fingers as some spark keys do.

Jack Gray's booklet, Bits of Wireless History, makes a passing reference to the origins of General Radio. In discussing the Clapp-Eastham "Boston" key, Jack states, "Eastham left the company inGR and Clapp-Eastham keys1915 to start General Radio Co. to supply the radio industry with high grade test equipment."  Thus we have a clue into the key's lineage and vintage.  The key pictured with the General Radio key is a Clapp Eastham "Boston" key.  Notice that the binding posts are almost identical.  The knurling on the adjusting screws are identical.  I doubt that this is coincidence.  Besides Eastham, the first employee of  General Radio was Knutt Johnson, a machinist paid 40 cents an hour, who had also worked at Clapp Eastham.  Perhaps Eastham took drawings and tooling with him or used the same parts or tooling suppliers.

We can say that this key was made between 1915 and the end of the spark era.  The Manhattan Electrical Supply Company's "Manual of Wireless Telegraphy #9", published in 1916 shows this key.  So we can get even closer in ascertaining the date.  MESCo lists the key without mentioning General Radio as the maker as "8479 Sending Key" for $10.00; the catalog rates the key at 15 amps at 110 volts.

Was this key targeted to the amateur market?  Being in the MESCo catalog, you would think so.  However, Clapp Eastham "Boston" keys with marble bases could be purchased for $6.50 for the ten amp version and $7.75 for the 20 amp version, considerably less expensive.  The Duck "Overland" key was less than half the price of the General Radio key.  Perhaps the General Radio key was intended for commercial use and was secondarily targeted to the amateur market.  The scarcity of the General Radio key compared to Clapp Eastham keys and other keys would indicate the General Radio key was not a big seller in the amateur market.

Melville Eastham was born  in Oregon in 1885.  As a youth, he built his on wireless station and was more interested in experimenting than operating.  In 1907, he partnered with J. Emory Clapp to form the Clapp - Eastham Co. making X-ray equipment.  The operation was transformed into making wireless components for amateurs as well for commercial enterprises.  Clapp Eastham's customer list had high profile names such as Fessenden and Armstrong.

Recognizing the need of the radio industry for measurement equipment, Eastham started General Radio.  The first facility was in Cambridge, Mass and the first catalog in 1916 lists a precision air variable and inductor, plus an absorption type wavemeter.  During W.W.I, General Radio made, among other items, large numbers of wave meters and crystal detectors for the United States government.

General Radio was at the forefront of test instrument innovation.  In 1924 General Radio invented the banana plug, which is still in use to day.  In 1928, they built the first vacuum tube voltmeter (VTVM) and in 1930 invented the first cathode ray tube oscilloscope.  GR's only radio, a crystal radio, was built the year the company was founded.  General Radio made it into the 21st century, although they changed their name to GenRad in 1975.  They were acquired by Teradyne in 2001.

My friend Lewis, a long time wireless collector on the middle east coast, had this key. I had tried to work trades with Lewis for many years and we were never successful. Then one day out of the blue, Lewis called me and said he was down sizing his collection and wanted to know if I would be interested purchasing a few items. I am not sure how many micro-seconds it took me to say "yes." I guess persistence pays off. Needless to say, I am quite pleased to have the little GR key in my collection. I am curious if anyone else has ever seen a key like this?

Thanks to Russ Kleinman for the MESCo. reference.


"GenRad home page.""

Gray, Jack. Bit of Wireless History from Gray History of Wireless Museum. G.J. Gray, 1969.

Manhattan Electrical Supply Co. Manual of Wireless Telegraphy #9, 1916.

Thiessen, Arthur E. A History of the General Radio Company 1915 - 1965. West Concord, Mass., 1965

William B, Duck, Catalog No. 11, Toledo, Ohio, 1915

For more information, visit the Telegraph Office home page

Neal McEwen,