A feature in this transmitter that is not found in the White transmitter is that both the front and the rear electrodes, in fact, the entire working portions of the transmitter, are insulated from the exposed metal parts of the instrument.  This is accomplished by insulating the diaphragm and the supporting cup 1 from the transmitter front.  The terminal 5 on the cup 1 forms the electrical connection for the rear electrode, while the terminal 6, which is mounted on but insulated from the cup 1 and is connected with the front electrode by a thin flexible connecting strip, forms the electrical connection for the front electrode.

Kellogg Transmitter.  The transmitter of the Kellogg Switchboard and Supply Company, originally developed by Mr. W.W.  Dean and modified by his successors in the Kellogg Company, is shown in Fig. 43.  In this, the electrode chamber, instead of being mounted in a stationary and rigid position, as in the case of the White instrument, is mounted on, and, in fact, forms a part of the diaphragm.  The electrode which is associated with the mica washer instead of moving with the diaphragm, as in the White instrument, is rigidly connected to a bridge so as to be as free as possible from all vibrations.

Referring to Fig. 43, which is a horizontal cross-section of the instrument, 1 indicates the diaphragm.  This is of aluminum and it has in its center a forwardly deflected portion forming a chamber for the electrodes.  The front electrode 2 of carbon is backed by a disk of brass and rigidly secured in the front of this chamber, as clearly indicated.  The rear electrode 3, also of carbon, is backed by a disk of brass, and is clamped against the central portion of a mica disk by means of the enlarged head of stud 6.  A nut 7, engaging the end of a screw-threaded shank from the back of the rear electrode, serves to bind these two parts together securely, clamping the mica washer between them.  The outer edge of the mica washer is clamped to the main diaphragm 1 by an aluminum ring and rivets, as clearly indicated.  It is seen, therefore, that the diaphragm itself contains the electrode chamber as an integral part thereof.  The entire structure of the diaphragm, the front and back electrodes, and the granular carbon within are permanently assembled in the factory and cannot be dissociated without destroying some of the parts.  The rear electrode is held rigidly in place by the bridge 5 and the stud 6, this stud passing through a block 9 mounted on the bridge but insulated from it.  The stud 6 is clamped in the block 9 by means of the set screw 8, so as to hold the rear electrode in proper position after this position has been determined.

[Illustration:  Fig. 43.  Kellogg Transmitter]