Radio receiver tubes

As mentioned in the introduction, the history of the vacuum tubes started in 1906. The first tubes, which were used only in military or research devices, were manufactured purely by hand and would be designed specifically for the device. After the start of public radio broadcast in the 1920s, the mass production of tubes started. The design of the first types was based on a light bulb. The electrode system was placed on a glass support, the filament served as a cathode - the so-called direct heating. The base used thick pins. At the beginning of the 1930s, indirectly heated tubes were launched. These use a metal tube as the cathode, inside of which the insulated filament is placed. This enabled the filament to be powered with alternating mains current and the radio receivers could get rid of the bulky and expensive batteries. The manufacturers unify their products and make electrically compatible types, although the look and the marking is different.

Since 1934, new side-contact "golden" tubes with unified marking are made in Europe. Since 1936, an important novelty was presented by the Philips company - the "red" tubes, which were visually similar to the golden ones, but the inner glass support was replaced by a glass disk, thanks to which the tubes were much smaller and their parasitic capacitances were lower. The Telefunken company has made the "steel" tubes since 1938. These used a steel envelope, electric connections are provided with glass leadthrough. The electrode system is placed horizontally.

Since 1941, "locktal" tubes are made. They leave behind the separate bakelite socket, the pins are attached directly into the glass bottom. A metal lead key serves as the ninth pin. Only a few types are made - ECH21, EF22, EBL21 and the series-heated UCH21, UF21 and UBL21. However, the properties of these tubes are so universal that they can be used anywhere, ranging from cheap simple radios to amplifiers, luxury radio receivers and industrial electronics. In Czechoslovakia, they are widely used until the end of the 1950s.

After the World War II, the products of military research come to consumer market, notably the "heptal" tubes. They are very small, only a glass bulb with seven pins. They are manufactured in Czechoslovakia since 1953. Seven pins are not enough for some purposes, so later the somewhat bigger "noval" tubes with nine pins come. Also a larger version, the "magnoval", is used for power tubes for TV receivers. These end the era of vacuum tubes in consumer electronics. All types of tubes were manufactured in hand, the workers would assemble the system of individual components. This limited the possibilities of miniaturisation. Automated transistor production brought massive cost reduction and speed increase of manufacture.

Many more types of tubes existed - octal, rimlock, supranoval, dekal and other. These were not widely used in our country.