It's a tuning capacitor. By the looks of the cotton wiring its been there since 1924
http://www.angelfire.com/scifi2/zpt/temp/radiola_3.jpg The Radiola 3 circa 1924 did not have tuning capacitors. It was tuned by rotating one coil within another. The range of this method was limited and movable jumpers were provided on the front to tune in the entire AM band. My #3 has a tuning capacitor and by the looks of the cotton wiring its been there since 1924. The model 3 is a super regenerative battery operated set. I guess they did not have line power then. The addition of the tuning capacitor was a big advancement. Who did it or was it original? http://www.angelfire.com/scifi2/zpt/temp/radiola_3.jpg The Radiola 17 circa 1926 is one of the first line powered sets. I have one that works. It is a type Tuned Radio Frequency. It does have three tuning capacitors. It does not have power electrolytic and instead of that has several large ac line chokes. It does not have AGC. Later models in the early 1930's were of type superhetrodyne, had electrolytic, tuning capacitors, and Automatic Gain Control. Jed by the looks of this, developments in electronics were doubling every 5 years for quite some time now. Frank z
