(Telephone) Holcomb's Improved Private-Line Telephones. Illustrated design on buff cover showing Holcomb's Duplex Amplifying Telephone, franked with 1881, 1¢ gray blue (s.e. at right) tied by Cleveland, O. oval handstamp, reverse with ad text and illustrations of Telephone Receivers, Very Fine. Estimate  $150 - 200. By far, the best known manufacturer of acoustic telephone equipment is J.R. Holcomb & Co. of Cleveland, Ohio. They designed and manufactured many different models of acoustic telephones, some exhibiting patent dates as early as 1878. $0 (Image)