manufactured is the use of a transmitter front that is struck up from
sheet metal rather than the employment of a casting as has ordinarily
been the practice. The formation of the supporting lug for the
transmitter from the sheet metal which forms the rear casing or shell
of the instrument is also an interesting feature.

Automatic Electric Company Transmitter. The transmitter of the
Automatic Electric Company, of Chicago, shown in Fig. 44, is of the
same general type as the one just discussed, in that the electrode
chamber is mounted on and vibrates with the diaphragm instead of being
rigidly supported on the bridge as in the case of the White or
solid-back type of instrument. In this instrument the transmitter
front _1_ is struck up from sheet metal and contains a rearwardly
projecting flange, carrying an internal screw thread. A heavy inner
cup _2_, together with the diaphragm _3_, form an enclosure containing
the electrode chamber. The diaphragm is, in this case, permanently
secured at its edge to the periphery of the inner cup _2_ by a band of
metal _4_ so formed as to embrace the edges of both the cup and the
diaphragm and permanently lock them together. This inner chamber is
held in place in the transmitter front _1_ by means of a lock ring _5_
externally screw-threaded to engage the internal screw-thread on the
flange on the front. The electrode chamber proper is made in the form
of a cup, rigidly secured to the diaphragm so as to move therewith, as
clearly indicated. The rear electrode is mounted on a screw-threaded
stud carried in a block which is fitted to a close central opening in
the cup _2_.

This transmitter does not make use of a mica washer or diaphragm, but
employs a felt washer which surrounds the shank of the rear electrode
and serves to close and seal the carbon containing cup. By this means