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Kellogg Fiddleback with Dial Added wiring diagram

Started by poplar1, November 20, 2013, 03:11:52 PM

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"C'est pas une restauration, c'est une rénovation."--François Martin.


Since another dial-equipped Fiddleback appeared on eBay, I thought I'd look at this to see how they added a dial on something this old. It's not a mystery, but a circuit diagram is a lot easier to understand than wiring.

Here is the circuit diagram, and a cleaned up/straightened version of the wiring diagram.

The circuit is a common-battery standard booster circuit much alike the Western Electric or anyone else's layout.  The transmitter (TX) circuit consists of the primary winding of the induction coil (P) and the transmitter in series between the line connections (L1, L2). Between the primary winding, we have the hookswitch HS1 that connects the circuit to the line when taken off-hook.  At the same time, by hookswitch HS2, actually just a fraction of a second later, the receiver is connected.

On the other side of the transmitter before the second line connection is the dial pulse switch that interrupts the now established local loop to produce DP signaling. While the dial is operational, i.e. wound up and rotating back, its off-normal contacts, DS1 and DS2, shunt the transmitter and receiver to provide a stronger pulse, and eliminate receiver clicking sounds.

The receiver is protected from DC entering by a condenser between L2 and the secondary winding (S) of the induction coil.

The ringer has a separate ringing condenser in series, both being connected directly between line L2 and ground.

For bridged ringing, the G terminal could simply be connected to L1, or the condenser wire moved from G to L1.

Removing the dial simply involves disconnecting the off-normal contacts from B, R, and D, and providing a wire jumper between R and L2.