There are numerous claimants to the title of the first company to produce practical transistor radios, often incorrectly attributed to Sony (originally Tokyo Tsushin Kogyo). Texas Instruments had demonstrated all-transistor AM (amplitude modulation) radios as early as 1952, but their performance was well below that of equivalent vacuum tube models. A workable all-transistor radio was demonstrated in August 1953 at the Düsseldorf Radio Fair by the German firm Intermetall. It was built with four of Intermetall's hand-made transistors, based upon the 1948 invention of Herbert Mataré and Heinrich Welker. However, as with the early Texas units (and others) only prototypes were ever built; it was never put into commercial production.