Main Line Sounding Relay 150 ohms by J. H. Bunnell & Co circ 1894
These sets were advertised in the “Journal of the Telegraph” dated March 20th 1894 and December 20 1898 and were described as follows:
The New Main Line Sounding Relay by J. H. Bunnell & Co gives more than three times the volume of sound given by the very best Box Relays or any other form of sounding relays for short or long main lines ever before produced.
They are unequalled for Wrecking Instruments, Testing Sets, Switchboard Sets, Temporary Offices and all places where it is desirable to dispense with the use of Local Batteries.
These instruments are made with full size relay magnets of 150 ohms resistance, having both magnet and armature adjustments and fully suited for doing, in a greatly improved manner, the work of regular main line box relays. They are highly sensitive to the weakest currents and will give a clear working sound on circuits where, without them, a relay with local sounder and battery would be absolutely necessary. This unit would be capable of working circuits from a mile or two up to 100 miles when with ordinary main battery power suitable for such lines they are equal to the best local sounders.
Price of 150 ohms resistance with key on base - $9.00.
Price of 150 ohms resistance without key - $8.00.