It was a hybrid design, using two miniature vacuum tubes as input stages and a single transistor as the output stage; this was required because the transistors at the time produced too much electrical noise. Even using one transistor considerably extended battery life, lowering the operating cost of the unit. As transistors improved, this model was replaced by all-transistor hearing aids.
- Fildes, Jonathon (2005-11-15). "Switching on the digital world". BBC News. p. 1. Retrieved 2007-11-16.
- http://www.hearingaidmuseum.com/gallery/Transistor%20(Body)/Sonotone/info/sonotone1010.htm Sonotone 1010 at the Hearing Aid Museum, retrieved December 30, 2009
- http://www.roger-russell.com/sonopg/sonopg.htm The Sonotone Corporation, retrieved December 30, 2009