Newest Old Radio: a 1920s Battery Set, the Dayfan OEM-7

A new addition to my collection arrived today. I’ve been reading the Elements of Radio to learn radio theory the way it was taught in the 1930s and 1940s, and many of the reference circuits in the book are the early circuits from the beginning of radio in the ’20s, so I’ve been interested in adding one of those to my collection both as an example of early technology, and to play with some circuit modifications.

The radio is the Dayfan OEM-7, a 4-tube reflexing tuned radio frequency receiver. It takes 4 ’01A tubes:

This radio dates from 1925, before frequencies and band markings were standardized. Each of the three large knobs is connected to a tuned circuit and the set of three are set in combination to tune a radio station’s frequency. The lower left is a variable coupler which rotates a coil around its axis to adjust sensitivity and volume, and on the right a rheostat to control the tube power to serve as a differently operating level control.

This particular radio is interesting because it uses a reflexing circuit design; there are 4 tubes in the circuit perform the work of 5 through a clever arrangement. This radio isn’t currently in working condition (like most of this age that haven’t been worked on) but there are only about a dozen parts in the entire thing so it shouldn’t be that challenging once I get around to fixing it up.

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