The Electro line was a separate line of guitars produced by the Electro String Instrument Corporation (Rickenbacker) and sold by Radio-Tel. They were sold to studios and dealers not carrying the full line of Rickenbackers. There were two Electro solid body models; the three quarter size ES-16 and the full scale ES-17. The ES-17 was similar to the Rickenbacker model 425 and the ES-16 was like the Rickenbacker model 1000. The Electro instruments usually had set necks (unlike the through necks of the equivalent Rickenbacker versions).

Early Rickenbacker instruments also carry the Electro brand name, The Electro String Instrument Corporation was founded in 1931 by Adolph Rickenbacker and George D. Beauchamp, to produce "Rickenbacker Electro Instruments".

Source: Rickenbacker history (7 April 2017)

Source: The History of Rickenbacker Guitars. Richard R Smith. 1987