Ionovac Plasma Tweeter 14A435A

A small volume of air, enclosed in the walls of a quartz cell, is ionized by a radio frequency voltage applied to the internal and external electrodes of the cell, while an audio signal from an amplifier modulates this RF voltage. As a result, the ionized air generates a purple glow in the cell and varies in volume in accordance with the variation of the acoustic signal. Coupled to a suitable horn, its performance level is comparable to a 30 cm woofer, and its frequency response extends from around 3,500 Hz to over 20,000 Hz.

Literally translated from "Radiorama" January 1962.

In questo link sono elencati 27 modelli, di cui 26 con immagini e 10 con schemi.
Elenco delle radio e altri apparecchi della DuKane Corporation; St. Charles (IL)