I imagine the rectifier was selenium which was bulky especially for higher amperage. Curious if the rectifier was placed in tender (whistle would be sacrificed?).
In Frank Ellison's words, "They're a little large, but they have ample capacity and work perfectly." (From "Delta Lines" in the August 1941 issue of The Model Railroader magazine.) He seemed very happy to find such an elegant solution to the problem.
Ellison attributed the "suggestion" to use this solution to Frank Arnaud of Milwaukee. He did not say anything about the whistle feature.
I was hoping to find the Mallory 1-B-8-C-1 rectifier in advertisements in the model railroad magazines of the that era but no luck so far. Google search didn't yield anything. The next place to look would be electronics magazines - if they existed back then - or perhaps Mechanix Illustrated, Popular Mechanics, or Popular Science of that era.