Casque de T.S.F.

Usage principal
Réception T.S.F.

Etat de conservation
En état de fonctionnement

• Informations supplémentaires

  Inscriptions
  PAT No 25 APRIL 1923
  
  DENespei tech (?)

  Remarques et commentaires
  
  

  Bibliographie
  

  — Patent US 1 447 969, granted on March 13, 1923, to Frederick Dietrich, of Flushing, New York, for a Telephone Head Set
  
  — Patent GB 196 225, granted on April 19, 1933, to C. Brandes, Inc. of New York, Assignee of Frederick Dietrich, for Improvements in Telephone Headsets