The rarest of the Western Electric cradle sets appears to be the 5 button, business base hand telephone. To date we have documented four models with this general configuration. There were three telephones designed for the 750A private branch exchange (PBX): the "105", the "205" and a later version of that same telephone. The "208" was wired for use in the 15A and 23A key telephone system (KTS).
The early "205" or "E4" handset mounting was a cradle set with a cradle very similar to a "B" handset mounting. The base of the cradle sat on a positioning ring/spacer that allowed the threaded portion of the shaft to pass through, align itself with the base and be retained to the base with a single nut as in other Western Electric desk telephones. The base appeared to be of the same general casting as the Western Electric upright dial desk stands and the "A" handset mounting. There are major differences that would not allow the interchanging of these bases. The "E" handset mounting had no grommet hole in the back of the base for handset and line cords to pass through. This occurred in the applique base below. There was a stamping in the back of the cradle base with the handset designation (eg. "E4"). In the three and nine o'clock positions of the base there were brass screw-blocks or "T blocks" that served to retain the cradle base to the applique base. The leather covered base cover was held to the applique base with two additional screws and did not come off when the cradle base was pivoted upward to make repairs or change cords. The cradle base pivoted upward at the twelve o'clock position on a sloppy hinge that was riveted to the cradle base with 2 brass rivets. This handset mounting supported an El handset and either a 2H or 4 H dial. The 537-type key equipment was contained in the applique base of the telephone set. The buttons on the applique base were marked 1, 2, 3, H, and L. The numbered buttons allowed selection of 3 central office trunks. The 750A PBX supported up to 15 stations. The "H", or hold button was a non-locking button that worked with an external relay and an internal bridging resistor. The " L" button was a button that did not have springs or a control lead on it and actually just insured that the trunk buttons were released. This put the telephone into a local talk path and allowed it to be used as an intercom. The applique base of the hand telephone also contained terminals for terminating the key equipment and handset. The E4 handset mounting was available in six standardized finishes: Black, ivory, French grey, old brass, statuary bronze and oxidized silver.
There were two arrangements for indicating incoming calls. One method was a different sounding bell for each trunk. The other system was a bell common to all trunks and trunk lamp indicators. This provided a visual signal with lamp caps that corresponded in hue to the line buttons on the applique base. This lamp indicator was available in all of the standardized colors. It is interesting to note that standard desk and wall sets were used with the 750-A PBX in conjunction with a separate 6009-type key unit. The key unit would be mounted on the wall or to the side of a desk, for example.
The "105" set was apparently the side-tone version of the "E4" handset mounting. The other features were alike. The later 6'205" sets were designated the "E7" handset mountings and were made to be comi3atibla with the 755-A PBX. The 755-A PBX allowed up to 20 stations and the "E7" would handle up to 4 central office trunks. The "E7" did not have the 295 ohm bridging resistor. The hold feature was now performed entirely in the key system box.
The "E5" set or "208" appeared identical to the other business base sets described above. This multi-button set was however designed for use in a key telephone system (KTS). The key telephone systems were called the 15A and 23A key telephone systems. The 15A system would accomodate I central office line and the 23A allowed 2 central office lines. The buttons on the "E5" handset mounting were labeled " l," "2,!' "H," "L," and "B". The line and hold buttons operate as they would in the "E4" or "E7" handset mountings. The intercom, however, was a manual "partyline" talk path and the "B," or "buzzer" button allowed the calling party to signal the other stations with a prearranged coding system. The 15A/23A KTS allowed for a maximum of 11 "E5" stations.
The "E" handset mountings did not have illuminated buttons and were not compatible with later private branch exchanges or key telephone systems. These telephones were ahead of their time in their use of a common talk pair and a few control leads. Automatic Electric had a separate talk pair in the line cord for every line on their AA-20 and AA-40 series multi-line business base telephones and there was no intercom.