One of my readers sent me a link to french article published in Audiophile n°4, April 1978 by Jon Hiraga.
Unfortuately I didn't understand french and the article is copied in pictures so translators would not work. But with the pictures and some interpretation I can write something about it.
This tweeter was produced by ONKYO in 1978.
Real ONKYO, 4-4-16 Ueno-Dori, Nada-Ku, 657 Kobe-City, Japan.
As ONKYO was famos with their wooden sides on their amplifiers the tweeter was also availible with wooden plinth.
Nothing really new, it was more or less a copy of the Ionofane.
A main transformer was used. The feedback for the self oscillating tube was done from the elektrode with a fixed capacitor. A resonant coil (L1) was used and had to be trimmed to resonance with C1/C2. The principle is a mix between the fixed Magnat oscillator and the Ionofane's floating oscillator. The ionic tip was different compared to the Ionofane. In the picture below you can see the two coils.