Army-navy preferred list of vacuum tubes

The accompanying Army-Navy Preferred List of Vacuum Tubes sets up a group of unclassified general purpose tubes selected jointly by the Signal Corps and the Bureau of Ships. The purpose of this list is to effect an eventual reduction in the variety of tubes used in Service equipment. It is mandatory that all unclassified tubes to be used in all future designs of new equipments under the jurisdiction of the Signal Corps laboratories or the radio and sound branch of the Bureau of Ships be chosen from this list. Exceptions to this rule are hereinafter noted.