Granted Patent
Utility
US 5,224,474 · App. 07/711,538
Retrofitting gas mask voice amplifier unit with easily actuated switch means
Inventor:
John Bloomfield
Patented Case
View Patent ↗
Granted: Jul 6, 1993
Filed: Jun 10, 1991
Inventor
John Bloomfield
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.