POSITION OF RHEOSTAT

Radio Record, Volume I, Issue 12, 7 October 1927, Page 15

POSITION OF RHEOSTAT

There are many radio diagrams that are practicaily identical except for the method in which the rheostats are connected. In some cases the rheostat is connected in the negative lead of the A battery, and in other diagrams it is shown in the positive lead. In some receivers the rheostat may be connected in either lead of the battery and equal results will be had; however, in audio amplifiers it is very important that the rheostat be in the negative lead, and it is equally important that the grid return from the amplifying transformers be connected directly to the negative of the A battery, rathan the filament of the valve. This is so that a negative voltage will be applied to the grid of the audio amplifier valve. Soft and Hard Valves. In the detector circuit when a soft valve is used best results will usually be had when the rheostat is connected in the positive lead of the battery, and then the grid return should be connected direct to the filament of the valve. When a hard amplifier valve is used as detector the rheostat should be in the negative lead and the grid return should be connected to the negative of the battery. The radio frequency amplifier valves in neutrodyne receivers are usually operated at zera grid voltage, and, theretore, if the and audio frequency valves are operated from separate rheostats, the theostat controlling the filament current of the radio frequency valves may be in either side of the line