Fig. 164. Galena Detector.
Such an arrangement is illustrated in Fig. 164. The base is a hard rubber block 3 3/4 x 1 3/4 x 1/2. The binding posts are of the type commonly used on electrical instruments. One of the posts is pivoted by placing a spring washer under the head of the screw which holds the post to the base. A short piece of brass rod fitted with a hard rubber knob passes through the wire hole in the post. A piece of No. 30 phosphor bronze wire is soldered to the end of the rod. By twisting the post and sliding the rod any portion of the mineral surface may be selected. Twisting the rod varies the tension of the contact.
The galena detector is connected in the receiving circuit in the same manner as other detectors of the mineral type.
THE AUDION.
The Audion—is finding favor in many amateur wireless stations, because of its almost entire lack of adjustment and of the loud clear signals which it gives even when used for long distance work.
The illustration shows the latest form of audion, the plate and the grid both being on the same side of the filament.
The filament of an audion is usually lighted by means of a six-volt storage battery. A small battery rheostat placed in series with the battery serves to regulate the amount of current flowing through the filament. Only one filament is used at a time, the other being saved as a reserve in case the first burns out.
Fig. 165. Audion.