English: Illustration on the cover of an electronics magazine of use of the first mass market vacuum tube hearing aids in 1933. Amplifying hearing aids, made possible by the invention of the triode vacuum tube by Lee De Forest in 1906, had just come on the market a few years before, and were a great improvement over previous crude electric hearing aids that used the amplifying ability of a carbon microphone. The hearing aid consisted of a box about the size of a loaf of bread, with a built-in microphone, that the user directed toward the speaking person, with a plug-in headphone. The illustration shows two hearing-impaired men using the hearing aids on a train. Alterations to image: Cropped out extraneous text on the cover.