The Sylvania 6SN7WGT was designed to be used by American military branches. Sylvania Electric Products was a U.S. manufacturer of diverse electrical equipment, including at various times radio transceivers, vacuum tubes, semiconductors, and mainframe computers. The Sylvania 6SN7WGT were made in the 1950s and early 1960s. They have a large brown colored base and large gettering. They meet military spec ratings for shock and vibration, resulting in improved microphone performance. The 6SN7WGTA replaced the earlier model. The 6SN7WGTA also has a brown base with a similar construction and is made to meet military specs. The Sylvania 6SN7 was used as an audio amplifier in the 1940-1955 period, usually in the driver stages of power amps. This vacuum tube was responsible for transmitting soundwaves through ham radios used within the field. This model could be used to replace many variations, including the Sylvania 7N7, RCA 1633, RCA 12SX7, the Sylvania 6180, and the 6SN7W. It has a 6.3V 600 mA heater. This dual triode vacuum tube has an 8-pin octal base. It provides a medium gain. It is basically two 6J5 triodes in one envelope. Originally released in 1939 it was officially registered in 1941 by RCA and Sylvania as the glass-cased 6SN7GT. Tung-Sol released their own 6SN7 shortly thereafter. Although the 6S-series are often metal-cased, there was never a metal-envelope 6SN7 (there being no pin available to connect the metal shield). There were, however, a few glass-envelope tubes with a metal band, such as the 6SN7A developed during World War II. Numerous variations on the model type have been offered over the years. These military specification vintage USA tubes provide dead quiet audio. They are open, musical, detailed, transparent, extended, and smooth. The octal tubes were used in vintage guitar amplifiers. The designer of the famous Williamson amplifier, one of the first true high-fidelity designs, suggested use of this model in his 1949 revision since it is similar to the original British single triodes, four of which were used in each channel of his 1947 circuit. Some keen current tube amp designers have used them as well. They have excellent audio and are very rugged. The 6SN7 was one of the most important components of the first programmable digital computer, the ENIAC, which contained several thousand of these. The SAGE computer systems used hundreds of 5692s as flip-flops. Sylvania was one of the companies involved in the development of the COBOL programming language. With the advent of television, the 6SN7 was well suited for use as a vertical-deflection amplifier. As screen sizes became larger, voltage and power headroom became insufficient. To address this, uprated versions with higher peak voltage and power ratings were introduced. The GE 6SN7GTA (GE, 1950) had anode dissipation uprated to 5.0 watts. The 1954 GE 6SN7GTB also had controlled heater warmup time which was better for series heater strings. The 6SN7 is considered to be obsolete by the 1960s, replaced by the 12AU7, and became almost unobtainable. With the introduction of semiconductor electronics, vacuum tubes of all types ceased to be manufactured by the major producers. A small demand for vacuum tubes in guitar amplifiers and very expensive high-fidelity equipment remained given their impressive audio capability. However, as existing stocks ran out, factories in Eastern Europe and China started to manufacture the 6SN7 and higher-gain 6SL7. As of 2012, 6SN7s were manufactured in Russia and China under the old Soviet designator 6N8S. Tung-Sol also put out a 6SN7 series from the 1940s-1960s.