With the introduction of the "solid back" transmitter of 1890, the Bell System was able to improve the transmission and began to replace the Blake transmitter. The early "two box" telephones were converted "three boxers" where the new transmitter arm replaced the middle box. These early conversions were used for long distance transmission through the 1890's while the older phones remained for local use.
The backboard measures 8 inches by 33 inches. The wood is 11/16 inchs thick. The top box measures 5 1/2 inches by 10 1/8 inches and contains a three bar magneto, a ringer and a switchhook. There was no induction coil in the top box since it was contained within the transmitter arm. The battery box, with a writing shelf, was a cover for a wet cell battery. This bottom box measures 6 3/4 inches by 11 1/4 inches.
The Western Electric Type 21 wall telephone was produced in 1897 and became the standard through the turn of the century. The number 229 transmitter was attached to a fairly large transmitter arm which contained an inducation coil in the 7 1/2 inch by 3 inch base (this arm is commonly called a #5 arm by collectors). The top boxes of the Type 21 and the earlier version were similiar. The most noticeable difference is the binding posts. The earlier posts were much smaller and were aligned vertically on the box whereas those of the type 21 were placed on angle.
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