larry@uunet.uu.net (Larry Lippman) (10/06/89)
In article <telecom-v09i0428m10@vector.dallas.tx.us> judice@kyoa.enet.dec.com (Louis J. Judice) writes: > This discussion reminds me: Is there any source out there for buying > a genuine new or used AT&T (WE) speakerphone Model 200? > These are the three piece units (Phone, mike and speaker) with a zillion > wires and cables protruding outwards. I don't know what a "Model 200" is, but from your description, might you be referring to the WECO 3A speakerphone or WECO 4A speakerphone? The WECO 3A speakerphone for standalone use consists of a 666-type transmitter unit with on/off switch and volume control, a 760-type loudspeaker unit, a 55-type control unit, and a 2012B transformer. This speakerphone could be used with any single or multi-line telephone set that could be wired for A-lead control (actually, the A-lead control could be eliminated, although this was not a standard Bell System wiring option). There were other options for this speakerphone system in which the transmitter could be incorporated within a Call Director or panel-type telephone set. The WECO 3A speakerphone used discrete transistor circuitry and was designed in 1960 and introduced around 1962. As far as I know, only WECO and Northern Electric (Telecom) manufactured the 3A-type speakerphone. The WECO 4A speakerphone consists of a 680-type transmitter, a 108-type loudspeaker, an interconnecting block, and a 85-type transformer. The amplifier and control unit was built into the 108-type loudspeaker. The WECO 4A speakerphone used integrated circuits and was introduced around 1974. As far as I know, the 4A speakerphone was manufactured by WECO and another firm, Precision Components Inc., who marketed the product as the PC-4A Speakerphone. Both of the above speakerphones employed amplified hybrids with voice-switched gain to minimize feedback. The complete concept of a switched-gain speakerphone is difficult to explain in this forum, but suffice it to say that the transmit and receive sides of the hybrid each have switchable gain which is adjusted so that the channel having the stronger signal has the higher gain. The result is that undesirable echo and singing is virtually eliminated. In addition, there is a compensation circuit for ambient room noise referred to as a NOGAD, Noise-Operated Gain Adjusting Device. The 3A-type speakerphone was the the epitome of clever discrete component design; as an example, the gain control was effected by a special silicon varistor bridge circuit called a "variolosser", whose effective insertion loss was controlled by a DC bias voltage. The 4A speakerphone was a more compact, improved version of the 3A speakerphone which looked a bit more "state of the art", but its operating principle was pretty much the same as its predecessor. While the 3A speakerphone is hardly state of the art, it does not sound too bad as long as one follows certain rules - like keeping the transmitter at least 30 inches away from the loudspeaker. The 55-type control unit in the 3A speakerphone is especially versatile, and I have modified them to do all sorts of things over the years using non-WECO transmitters and loudspeakers. I have utilized the 55-type control unit as the heart of various door-answering and other types of handsfree intercom systems. > I've had these units in my office, along with newer AT&T (System 75/85 > compatible sets), and I don't think anything has ever rivaled their > quality or durability. Fortunately I have one in my office now, but > I'd like to get one for my home office. I agree! I still have 3A speakerphones in my house and in my office at one of our facilities. I think they still sound great, and may even sound better than the fancy Northern Telecom SL-1 electronic handsfree telephone in my office at another facility location. I don't know where you can obtain any of the above speakerphones, but they do appear surplus from time to time. While I don't care to part with any extra units that I have, I would be willing to furnish the complete schematics and technical data should you manage to obtain one. <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> TEL 716/688-1231 | 716/773-1700 {hplabs|utzoo|uunet}!/ \uniquex!larry <> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"