DeForest CF-185 Tube
|Shown here is a
type CF-185 tube made for the U.S. Navy by the DeForest Radio Telephone
& Telegraph Company, probably in 1917. The "CF"
prefix was the Navy's designation for any item made by DeForest.
The early examples of the CF-185 featured the 3-pin base that was, for a time, the Navy standard. The bayonet pin was the fourth connection. Later tubes used the 4-pin Army Signal Corps base, which became known as the UV base in the early 1920's.
Much of the early DeForest equipment was originally designed to use the screw-base spherical Audion tube. To use the CF-185 in such applications, an adapter as shown below could be used. The two wires were for the filament connections. This tube is about 5 inches long, and 1 1/4 inches in diameter.
Etched into the glass is a warning to not exceed 0.85 amps current through the filament, which was an oxide-coated tungsten wire. Though the construction was far more sophisticated than that of the Audion, the roughness visible in the plates is proof that DeForest was still building his tubes almost entirely by hand.
Scratched into one of the plates is the number 1253, which must be a serial number. Records that have survived indicate that only about 2200 of these tubes were delivered to the Navy.