Pratt

The name Pratt in this entry refers to Harry Preston Pratt and the Pratt Radio Tube Co. of Chicago, not to a similarly named British business. Pratt was a physician and inventor interested in scientific instruments and electrotherapy before turning to radio. In the early 1920s he studied electron tubes and other components for reception. A newspaper in December 1923 presented one of his single-ended tubes with a UV base; Pratt credited it with controlling electron flow in a way that reduced noise and distortion. These were the inventor's claims, not independent comparative tests. Pratt Radio Tube Co. appeared among exhibitors at the Chicago radio fair in November 1924: the name therefore had a commercial presence, although the scale of manufacture remains uncertain.

The most tangible product of the line is the D-1 detector tube, documented by a surviving specimen with a box and instruction sheet bearing the Pratt Radio Tube Co. name. It is a triode with a four-pin UV base and bayonet fitting; the catalogued version specifies a 5-volt, 0.25-ampere filament. Production quantities are unknown, and the actual maker of the tubes has not been securely identified. Pratt filed an application in 1923 for another, double-ended arrangement; its patent was granted only in 1936. A patent application describes an invention but does not by itself show that the version was sold. A further alternating-current tube design, filed in 1928 and patented in 1937, used concentric glass envelopes to separate heating from the electrodes; commercial production of this design is likewise undocumented.

Pratt's inventive activity also covered a selective receiver, a shield for radio apparatus and even a vanity case incorporating a radio. These ideas place the D-1 within the work of a versatile experimenter, but they do not turn every patent into a Pratt product. This entry therefore retains the Pratt name as a route to the valves actually identified and their documentation, distinguishing the surviving D-1 from patented designs and separating the Chicago company from Pratt & Co. of London, which is not shown to be connected with this American line.