TUBE RADIOS CLASSIFICATION

I. THE ANTIQUE CIRCUITS

          Crystal Radios
          These primitive RECEIVERS work with a crystal (lead sulphate), a natural mineral which works as a semiconductor.

          Crystal radios don’t need electric energy source to work, and the sound is reproduced by a pair of phones. They resisted time, being industrialized until the 1930s, in regions where there wasn’t electric energy. On the side picture, a crystal radio (detektor-empfänger), brand name Heliogen, made in Germany, in 1932, from the author’s collection.


          Regenerative Radios
          The greatest radio circuit creator, Edwin Armstrong, invented the regenerative circuit in 1912. The regeneration principle is a feedback: part of the radiofrequency is fed again to the circuit input, increasing sensitivity and selectivity.

          Lee de Forest, the first radio tube creator, had a judicial fight against Armstrong about the regenerative invention, until 1934, when the United States Supreme Court decided victory to Forest,  going against the entire scientific community. Armstrong committed suicide in 1954. On the side picture, the regenerative model 453 Linsdström with Telefunken licence to use valve. This monovalve was made in Germany, in 1924 (author’s collection).

          TRF Radios– Tuned Radio Frequency
          Tuned Radio Frequency-TRF, was created in USA by Swedish Ernst Alexanderson, in 1916. The radiofrequency is tuned and amplified for many stages, until the audio detection and output. This circuit problem is the capacitance between the tubes electrodes, causing oscillations and interferences.

          Many TRF radios can be identified for its long and short cabinets, with a top access to the circuit, and a series of big internal coils. The picture on the right shows, a TRF Atwater Kent, model 46, made in1928, from the author’s collection. 


         Neutrodyne Radios
         The radio with a neutrodyne circuit is a particular kind of TRF, in which the effects of internal capacity
between the plate and the grid are reduced.  Louis Hazeltine, born in the United States in 1886, created and patented the system (1922/23). He put filters that neutralizedthe noises caused by tubes oscillation. The neutrodyne was the first receiver suitable for public commercialization. In 1927, 10 million of neutrodynes are believed to have been built. On the side picture, a Freed-Eisemann receiver, model NR-9, from 1927, with neutrodyne circuit. Courtesy of Bill Kendrick (www.antique-radios.net), Antique Radio Pictures.

        TRF circuit – Second generation
        A new tube conception with an auxiliary grid (screen-grid) was inserted in the circuits since 1927, solving oscillation problems making the neutrodyne circuit obsolete. 
As an example, the picture on the right shows a radio name brand Detrola, model 121, from 1936, from the author’s collection.





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