Fig. 97. Shoemaker Detector Circuits.
The Shoemaker system makes use of a loop aerial, and the circuits with a single and double coil tuner are illustrated in Fig. 97. It is not necessary to use these, and the detector will operate just exactly as well on a "straightaway" aerial.
Lamp Detector.—All electrolytic detectors, more especially those of the "glass point" type, are subject to the annoyance of "burn-outs." That is, the fine platinum wire melts when receiving strong signals from a near-by station.
In such case, the "bare point" must be lowered until it again makes contact with the liquid, and the "glass point" reground until the wire is again exposed.
When this trouble comes often it is very convenient to have at hand a simple detector which will not burn out and which may be substituted for the usual one when great sensitiveness is not required.
Fig. 98. Lamp Detector.
Such an instrument is made by snipping off the tip of a small incandescent electric lamp and removing the filament with a wire. One of the leading-in wires is broken off as close as possible to the glass stub and the globe half filled with a 20 per cent acid solution. The broken wire must be made the negative or cathode and connected like a Fessenden or Stone detector. This lamp detector though crude will give good service without burning out when used to receive from near-by stations.
In place of a lamp detector, a glass point having a larger wire than that of the cigar lighter may be used instead of the usual point, but it will not be so sensitive.