These early receivers have a PW-D micrometer dial that has a bluish-gray Index dial and an inner Number dial that is red with white numerals. The matching loudspeaker is the early style cabinet with a 10" Rola K electrodynamic speaker only available for the production. History of the Design and Production Many radio engineers of the thirties firmly believed that the absolute best sensitivity and stability of a communication receiver's RF amplifier, First Detector and Local Oscillator could only be achieved by using "plug-in" coils. This type of approach eliminated problems of lead length, shielding and stability along with isolation of unused tuned circuits - problems that were commonly found in broadcast receivers using conventional rotary bandswitches. Plug-in coils were a hassle, no doubt.
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Artwork drawing of the 51J-4 from the manual Many Collins Radio enthusiasts believe the 51J Series comprises the best looking receivers that the company produced - but, what about 51J performance? Like many pieces of collectible vintage electronic gear, the 51J receivers are now over half-a-century old. Many users are operating their 51J receivers in "as-found" condition. Are they experiencing all that the 51J is capable of? The following article details how to get the most out of your 51J receiver.
Robert Hooke invented a string telephone that conveyed sounds over an extended wire by mechanical vibrations. It was to be termed an 'acoustic' or 'mechanical' non-electrical telephone. Charles Morrison proposes the idea that electricity can be used to transmit messages, by using different wires for each letter. Innocenzo Manzetti first mooted the idea of a "speaking telegraph" telephone. Charles Bourseul writes a memorandum on the principles of the telephone.
Acoustic telephone ad, The Consolidated Telephone Co. Innocenzo Manzetti first mooted the idea of a "speaking telegraph" or telephone. Use of the "speaking telegraph" and "sound telegraph" monikers would eventually be replaced by the newer, distinct name, "telephone". Charles Bourseul published an article in the magazine L'Illustration Paris: