It is obvious, therefore, that in the “in-tune” system the electromagnetic effect on the armature should, when the armature is closest to the pole pieces, be of such an overpowering nature as to prevent whatever accelerating tendency the gongs may have from throwing the armature out of its “stride” in step with the current.  For this reason it is usual in this type to so adjust the armature that its ends will actually strike against the pole pieces of the electromagnet when thrown into vibration.  Sufficient flexibility is given to the tapper rod to allow it to continue slightly beyond the point at which it would be brought to rest by the striking of the armature ends against the pole pieces and thus exert a whipping action so as to allow the ball to continue in its movement far enough to strike against the gongs.  The rebound of the gong is then taken up by the elasticity of the tapper rod, which returns to an unflexed position, and at about this time the pole piece releases the armature so that it may swing over in the other direction to cause the tapper to strike the other gong.

[Illustration:  Fig. 181.  Tappers for Dean Ringers]

The construction of the “in-tune” harmonic ringer employed by the Dean Electric Company, of Elyria, Ohio, is illustrated in Figs. 180, 181, and 182.  It will be seen from Fig. 180 that the general arrangement of the magnet and armature is the same as that of the ordinary polarized ringer; the essential difference is that the armature is spring-mounted instead of pivoted.  The armature and the tapper rod normally stand in the normal central position with reference to the pole pieces of the magnet and the gongs.  Fig. 181 shows the complete vibrating parts of four ringers, adapted, respectively, to the four different frequencies of the system.  The assembled armature, tapper rod, and tapper are all riveted together and are non-adjustable.  All of the adjustment that is done upon them is done in the factory and is accomplished, first, by choosing the proper size of weight, and second, by forcing this weight into the proper position on the tapper rod to give exactly the rate of vibration that is desired.

[Illustration:  Fig. 182.  Dean In-Tune Ringer]

An interesting feature of this Dean harmonic ringer is the gong adjustment.  As will be seen, the gongs are mounted on posts which are carried on levers pivoted to the ringer frame.  These levers have at their outer end a curved rack provided with gear teeth adapted to engage a worm or screw thread mounted on the ringer frame.  Obviously, by turning this worm screw in one direction or the other, the gongs are moved slightly toward or from the armature or tapper.  This affords a very delicate means of adjusting the gongs, and at the same time one which has no tendency to work loose or to get out of adjustment.

[Illustration:  Fig. 183.  Kellogg In-Tune Ringer]

In Fig. 183 is shown a drawing of the “in-tune” harmonic ringer manufactured by the Kellogg Switchboard and Supply Company.  This differs in no essential respect from that of the Dean Company, except in the gong adjustment, this latter being affected by a screw passing through a nut in the gong post, as clearly indicated.