Don't set the transformer of a transmitting set nearer than 3 feet to the condenser and tuning coil.
Don't use a rotary gap in which the wheel runs out of true.
RECEIVING DON'TS
Don't expect to get as good results with a crystal detector as with a vacuum tube detector.
Don't be discouraged if you fail to hit the sensitive spot of a crystal detector the first time--or several times thereafter.
Don't use a wire larger than No. 80 for the wire electrode of a crystal detector.
Don't try to use a loud speaker with a crystal detector receiving set.
Don't expect a loop aerial to give worthwhile results with a crystal detector.
Don't handle crystals with your fingers as this destroys their sensitivity. Use tweezers or a cloth.
Don't imbed the crystal in solder as the heat destroys its sensitivity. Use Wood's metal, or some other alloy which melts at or near the temperature of boiling water.