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This key style was very popular and other examples can be seen in the "Hand Keys" section below (although these are later, inexpensive keys.) These are the standard WWII hand key.
The J-38 and J-47 were found in many different environments during WWII.
In 1919, Bunnell introduced a large base radio hand key that was called the Straight Line Radio Key.
This large version had a set of auxiliary contracts that closed with the key lever up and opened with the key lever down, or, the opposite of the sending contacts.
There were various owners after Jesse Bunnell's death but the company did continue on with other owners.
Bunnell was sold to INSO Electronic Products in 1960 and then to it's current owners, MNJ Industries, in 1989.
The knob became the standard for early radio telegraph keys for the Signal Corps, especially those keys from Brach - see the Brach J-5-A below in "Flame-proof Keys." Made for U. Shipping Board in 1920, these large keys used .625" diameter silver contacts to handle the high currents of spark transmitters.
The brass ring around the lower contact is a "cooling ring." The base is made of hard rubber.
The J-6 was used by the Signal Corps for the small airborne spark transmitters that were in use at the end of WWI up into the early 1920s.
The J-47 is typically found without the shorting lever installed even though the stationary part of the switch is present.
This was because the J-47 was primarily a "radio key." J-38 keys always have the shorting lever since they were primarily a "land line key.".
This key is fitted with a rubber cable and PL-68 connector which indicates it was going to be used with military equipment. Many of the military keys were used with transmitters that were cathode keyed and sometimes had significant voltage on the key itself.
Also, other types of equipment may have voltage levels or current levels that could cause sparking when the key breaks contact.
Originally the SE68A was a "leg-key," that is, it had long threaded rods on the bottom of the key base that allowed direct mounting to a table with connections made to the rods from under the table.