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J-37 Keys
The Telegraph Keys That Won The War?!

During WWII, the Korean War, and even into the Vietnam era the U. S. Signal Corps designated many of their telegraph (Morse code) keys with a "J-" and a number. The real workhorse key during those years was the J-37. There are many more glamorous wartime keys around, but the keys that carried the bulk of the action were the J-37 keys. The J-37 key is unusual because, with the addition of different bases and connections, it became part of other more special purpose keys. All the keys shown below are based on the J-37.

The J-37 Family of Keys

In the descriptions that follow you can click on the blue links to see more detailed pictures and get more information on each key. Another excellent source of information on J-37 keys is "The Vail Correspondent" which you can get from Tom French at Artifax Books. Issues #4, #5, and #14, all contain information about J-37 keys.

Front and center in the picture above is the basic J-37. It has a small, light frame made of black phenolic resin. The electrical connections are easily accessed metal straps fastened directly to the binding posts, with the leaf spring serving as one of the connections. The characters "J-37" are molded into the top left, front of the frame. The trunnion posts are also molded into the plastic frame, and the button, lever, and adjusting screws are standard triumph key design. There is a Japanese copy of the J-37 which has the words "Soling Japan" molded into the bottom and does NOT have "J-37" molded into the top.

In the upper left corner of the picture is the J-37 Mae West. The base for this key has an extended set of binding posts on the rear for attaching a long set of connecting wires, and indentations on each side to allow the wires to be wrapped around the base of the key for storage in a training set. This key was not given its own "J-" number as was done in most other cases when the J-37 was put on a special base, so the imaginative GI's found their own name for it.

Second from the top on the left side of the picture is the J-43. In this case the standard J-37 is on a rectangular base stamped with a white "J-43" on the left side and a large toggle switch on the right side. The toggle switch is marked "OPEN" at the back and "CLOSED" at the front. The J-43 also has an additional binding post, marked "RELAY", and a small metal wicket mounted on the right rear of the base. The toggle switch has no effect on the normal operation of the key, but when the switch is set to CLOSED there is continuity between the "GND." (left) terminal on the frame and the "RELAY" binding post on the right rear of the base. There is a rare variation of the J-43, which has a fancy plunger/release switch in place of the normal toggle switch. Looks like a committee got involved in the design!

The third key on the left side of the picture is a J-44. The base has "J-44" stamped in white on the left front, and a small slide switch on the right side which is marked "VOICE" at the back and "TELEG" at the front. The slide switch acts as a circuit closer, shorting the two binding posts when in the "VOICE" position.

At the bottom left in the picture is the J-45. This is the well known "leg clamp" key consisting of a J-37 mounted on a metal plate hinged to a spring metal, inverted "U" shaped clamp made to fit snugly around the thigh of a seated user. It is usually found with the cable intact, and makes a great mobile key for ham radio use. Later models were designated as KY-116/U rather than J-45. There are two rare variations of the J-45, the J-45FR and the JJ-45. Now, thanks to Guenter (DL1HQE), we know of a J-45-GY (Germany?), which you can see at his web site. I have never seen or heard of another of J-45-GY.

In the center on the right side of the picture is the most "plain Jane" of all keys, the J-47. In this case the J-37 frame is mounted on a black bakelite base with nothing else on it except "J-47" stamped in white on the left side. There are two notable variants of the J-47, the first with rounded corners and "J-37" molded, rather than stamped in white, on the base, and the second, known as the Lionel J-47, which is a strange combination of a Lionel J-38 frame and a J-47 base.

At the top right of the picture is an unusual key with the designation J-48-A. This key consists of a J-37 mounted on a flat army drab metal plate, a short cable terminated with a 1/4" phone plug, and a cover which is held in place by two screws. The characters "J-48-A" are stamped into the front of the bottom plate, which also has slots in it for mounting on a surface with matching studs. There also exists a model J-48 (no "-A") which looks the same on the outside, but does not have a J-37 on the inside. You can see a J-48 and what the key inside looks like on Tom Perera's Web Page.

Key and Plug Assembly No. 9. I was unsure of the proper designation for the key at the bottom right of the picture. The base of the key is stamped "KEY AND PLUG ASSEMBLY NO. 9" but in the N7CFO "Keyletter" #28 there are copies of an advertisement from the June 1943 issue of Electronics Magazine in which this key is identified as the B-19. Fortunately I got an email from Chris Bisaillion, VE3CBK, who is a collector and restorer of Wireless Set No 19 equipment. He researched and wrote an article about keys for the Wireless Set No 19. Chris's information makes it clear that the key is properly called "Key and Plug Assembly No 9". This key, like the J-45, was apparently intended for mobile use, fastened to the leg of the operator with two web straps. It is mounted on a thin aluminum base and has a black aluminum cover secured by 4 sheet metal screws.

Last, but certainly not least, at the top center of the picture is the Telegraph Set TG-5-B with its attached J-41-A key. Technically this device does not use a J-37 key, but the J-41-A is close enough for me. To the best of my knowledge this device was used for connection to wired telegraph circuits. The key contains an extra terminal and is wired such that the back terminals have continuity when the key is up and the two terminals on the right side of the key have continuity when the key is down.

Not shown in the picture above are the Radio Marine Corporation Covers for J-37's which were used with transmitters that placed a high voltage on the key contacts. I have an RM-24 and Herman,VK2IXV, was nice enough to let me use a picture of his RM-28.

Finally, just for fun, and as an example of what a creative ham radio operator can do with military surplus keys, here is a Combination Paddle/Straight Key which was probably put together out of a well stocked ham junk box.

J-37 keys are small, light, and tough as nails. Their size and construction make them an excellent choice for a backup or portable key. Many people think that leaf springs, which are used on the J-37's, have better mechanical characteristics than coil springs (which are used on keys like the J-38 and Speed-X hand keys) and therefore prefer the J-37 keys.

With a little patience an excellent J-37 key can be purchased for a reasonable price at flea markets, hamfests, and on-line auctions. Unless you buy a key from an experienced key collector, do not take the seller's word that the key "seems to be complete", or "appears to have no missing parts". Examine the detailed pictures for the type of key you intend to buy to make sure you can recognize any missing or broken parts.

EMail: scott(at)
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