Types of Air Whistles
Hancock offered three different models of their air whistle. The most common was the 4700, which consisted of the whistle along with a large, rectangular bowl in the same plane as the languid plate. This bowl, or reflector, is used to project the sound of the whistle ahead of the locomotive, instead of omnidirectional as in the case of most whistles. The second model was the 4700-2. This whistle is basically the same as the 4700 except that it has an electric heating element installed in the bowl to keep it from freezing. The final offering was the H4700, which did not include the reflector bowl. Aside from this difference, it is basically identical to the 4700.
The Hancock air whistles were all designed so that the bell of the whistle is horizontal when mounted on a standard horn mount. All the whistles are a single-bell chime, playing the notes E A C# (A major triad) when blown on air. However, over time, many of the whistles got off-key and produced some variants. One common chord was E A D.
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