roy@alanine.phri.nyu.edu (Roy Smith) (08/20/90)
OK, here's a question that's been bothering me for probably
about 20 years. Why, on a standard 500/2500 handset, does the
microphone just drop in but the speaker have screw terminals?
Roy Smith, Public Health Research Institute
455 First Avenue, New York, NY 10016
roy@alanine.phri.nyu.edu -OR- {att,cmcl2,rutgers,hombre}!phri!royChristopher Owens <owens@cs.uchicago.edu> (08/22/90)
In article <11093@accuvax.nwu.edu>, roy@alanine (Roy Smith) writes: > OK, here's a question that's been bothering me for probably >about 20 years. Why, on a standard 500/2500 handset, does the >microphone just drop in but the speaker have screw terminals? The microphones on 500/2500 handsets were (still are?) made using a pellet of tightly-packed granulated carbon as the transducer. These pellets go bad (mechanical wear? environmental contamination?), resulting in lousy fidelity. A phone in this state can often be brought back to prime condition for a short while by giving the handset a rap on the desktop. But eventually the microphone needs to be replaced. It's about the only part of a 500 or 2500 that doesn't last forever. Someone at Bell undoubtedly decided that, since they expected to own the phones forever, the money spent at the factory on the drop-in mount would be more than paid back in savings of the repairman's time.
Rob Warnock <rpw3%rigden.wpd@sgi.com> (08/22/90)
Just a guess: I suspect that the failure rate for carbon microphones is *far* higher than electrodynamic earphones, thus the "quick-change" connection. Rob Warnock, MS-9U/510 rpw3@sgi.com rpw3@pei.com Silicon Graphics, Inc. (415)335-1673 Protocol Engines, Inc. 2011 N. Shoreline Blvd. Mountain View, CA 94039-7311
hrs1@cbnewsi.att.com (08/22/90)
In article <11093@accuvax.nwu.edu>, roy@alanine.phri.nyu.edu (Roy Smith) writes: > OK, here's a question that's been bothering me for probably > about 20 years. Why, on a standard 500/2500 handset, does the > microphone just drop in but the speaker have screw terminals? The "standard" 500/2500-type handset is/was the G-type handset. It originally had a U-1 ring armature receiver, but I forgot the code for the carbon trans- mitter. Note the use of the terms "receiver" and "transmitter", rather than speaker and microphone. The receiver is an electromagnetic device, and rarely fails during the life of the telephone set. The carbon transmitter depends on the action of the carbon granules, which have to remain mobile. They have a tendency to pack, however, especially if the fone is used in the same position for a long time. This often happens in a wall phone. While this can often be fixed by banging the handset against a hard object, it is an easy matter to open the handset and slip in a new transmitter capsule. New telephone sets now usually have electromagnetic ot electret transmitters, and the handsets cannot any longer be opened. Herman Silbiger
Julian Macassey <julian@bongo.uucp> (08/23/90)
In article <11093@accuvax.nwu.edu>, roy@alanine.phri.nyu.edu (Roy Smith) writes: > OK, here's a question that's been bothering me for probably > about 20 years. Why, on a standard 500/2500 handset, does the > microphone just drop in but the speaker have screw terminals? > Well, not only do 500 and 2500 sets have drop in microphones (Transmitters in telco speak), but all Western Electret sets using a carbon transmitter use the same device called a T1. Do not confuse a T1 transmitter with "T1 carrier". The reason for the easy removal of the transmiter is for simple field replacement. Carbon transmitters go bad more often than "speakers", known as receivers in telco speak. The following countries also have drop in transmitters, Denmark, Sweden, UK (old phones) Germany. There are no doubt others that I am not familiar with. Denmark also used to have drop in receivers. Julian Macassey, n6are julian@bongo.info.com ucla-an!denwa!bongo!julian N6ARE@K6IYK (Packet Radio) n6are.ampr.org [44.16.0.81] voice (213) 653-4495