OCR Text |
Show Standard Type of Tuned Radio-Frequency Outfit The growing tendency to use high voltages in audio frequency amplifiers often results in the application of the same voltages to the radio frequency fre-quency tubes, due to the fact that separate sep-arate binding posts for the radio frequency fre-quency and audio frequency "E" positive posi-tive taps are not provided for in many sets. The accompanying illustration shows a convenient r.-nd practical method of varying the voltage on the radio-frequency tubes, by the use of a high resistance. The circuit shown is not new, but is a standard type of tuned radio-frequency outfit, illustrated to show where the high resistance should be , i P o I ."Method of Varying Voltage on Radio-Frequency Radio-Frequency Tubas. connected In such a set. The same . Idea is applicable to Intermediate stages of a superheterodyne or to other forms of radio-frequency amplification. amplifi-cation. Where the amplification voltage is between 00 ai d 13"i the resistance may be L'u.i.'niO ohms mr.-ximum, although much lower values usually will give the desired results. The principal point to be considered In choosing such a resistance re-sistance is its ability to go down to : fairly low values of resistance. Xote that the variable resistance Is connected in series with the supply to the radio frequency tubes only, the 90-volt tap in the illustration connecting connect-ing to the audio frequency tubes directly. di-rectly. Any variable resistance of suitable value may be used in this manner to control voltage on It. F. tubes. The illustration il-lustration shows the Centralab resistance. re-sistance. The Bradleyohm and the Clarostat are others which should serve satisfactorily. Cleveland News. |