US PATENT SUBCLASS 178 / 71.12
.~.~ Vacuum tube and relay

Current as of: June, 1999
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178 /   HD   TELEGRAPHY

70 R  DF  REPEATERS {16}
71.1  DF  .~ Automatic in either direction {14}
71.12.~.~ Vacuum tube and relay

DEFINITION

Classification: 178/71.12

Vacuum tube and relay:

(under subclass 71.1) Telegraph repeaters using a space discharge tube and an electromechanical operated contact.