Radio broadcast .. (1922-30)

288 Radio Broadcast used in a standard socket the capacity of the adapter employed added to the capacity of the tube makes it practicable without changing the circuit. This tube is particularly suited for portable sets in which it is necessary or desirable to use ordinary dry cells, or flashlight cells for filament operation. The small electrical capacity between the electrodes makes it a very satisfactory tube for radio-frequency amplification. This tube does not require critical adjustment of plate voltage, and tapped plate batteries are not necessary, whether the tube is used as a detector or as an amplifier. THE UV-2OO AND C~3OO THESE tubes are particularly desirable for the skilled radio experimenter interested in code work and reception over great distances. They are not suitable for dry-cell operation because the filament requires one ampere at five volts. Their action as a detector is very critical with respect to filament voltage and plate voltage, and is not as uniform between different tubes of the same type or as constant in any one tube as in the case of the high-vacuum tubes (UV199, C-299, UV-20I-A, and 0-301 -A). They are very sensitive to weak signals, especially spark and modulated CW signals, when skillfully handled by experienced operators in a circuit particularly equipped for the proper voltage operation of filament and plate. They are not recommended for audio or radio-frequency amplification and should never be used with a plate voltage greater than that obtainable from a 22|-volt B battery at full voltage. These tubes require a little patience and skill in adjustment for the reception of weak signals. Under certain conditions they have a tendency to be slightly more noisy in operation than either of the high-vacuum tubes which are practically free from such disturbances. UV-2OI-A AND C-3O I -A THESE tubes are powerful amplifiers, inherently better than the UV-199, and are particularly suitable for loud-speaker operation. They are designed to give the best possible amplification for general use, their amplification property not being sacrificed to any extent to give a minimum of filament energy. The operation of these tubes is almost free from variations caused by slight changes in plate and filament voltage. Accordingly, they are quiet in operation and have a longer operating life than any of the tubes mentioned above. They are equipped with a standard base and thus fit in many sets already constructed, unless they have been made especially for UV199'$, C-299's, or WD-i 1's. The filaments require a much greater amount of electrical energy for their operation than does the UV-199 or 0-299, but the UV-2OI-A and €-30 1 -A tubes can be operated from dry cells in the case of one or two tubes used only a few hours per day at a lower expense than with the use of a storage battery. As an audio-frequency amplifier, these tubes are somewhat superior to the UV-199 or 0-299. As a detector, the UV-2OI-A or 0-30 1 -A are about the same in response as the UV-199 or 0-299 and are to be recommended over the UV-2OO for most general purposes, except in equipment specifically designed for the latter tube as regards potentiometer adjustment for plate voltage and very fine adjustment for filament voltage. The UV-2O1-A and 0-301 -A are ideal for a one-tube set employing dry cells or a multi-tube set when a storage battery is available for filament operation. Critical adjustment of filament and plate voltages are not required and it is not necessary to have taps on the plate batteries. Although the capacity between the electrodes of the UV-20I-A and 0-301 -A are somewhat greater than the UV-199 and 0-299, their greater inherent amplification makes them just as satisfactory in most radio-frequency amplifier circuits. When used for audio-frequency amplification, a negative grid bias or C battery should be used [see page 80, RADIO BROADCAST for Nov., 1923], the C battery voltage depending upon the plate voltage employed. The following table gives the correct value of C battery with different plate voltages: PLATE VOLTAGES 40 60 80 1OO 120 C BATTERY VOLTAGE 0.5 to i.o i.o to 3.0 3.0104.5 4.5 to 6.0 6.0 to 9.0 (not to be used with UV-i99's or 0-299'$.)