_Don't_ overload an oscillation vacuum tube as it will greatly shorten its life. Use two in parallel.

_Don't_ operate a transmitting set without a hot-wire ammeter in the aerial.

_Don't_ use solid wire for connecting up the parts of transmitters.

Use stranded or braided wire.

_Don't_ fail to solder each connection.

_Don't_ use soldering fluid, use rosin.

_Don't_ think that all of the energy of an oscillation tube cannot be used for wave lengths of 200 meters and under. It can be if the transmitting set and aerial are properly designed.

_Don't_ run the wires of oscillation circuits too close together.

_Don't_ cross the wires of oscillation circuits except at right angles.

_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.

_Don't_ forget that strong static and strong signals sometimes destroy the sensitivity of crystals.

_Don't_ heat the filament of a vacuum tube to greater brilliancy than is necessary to secure the sensitiveness required.

_Don't_ use a plate voltage that is less or more than it is rated for.

_Don't_ connect the filament to a lighting circuit.

_Don't_ use dry cells for heating the filament except in a pinch.

_Don't_ use a constant current to heat the filament, use a constant voltage.

_Don't_ use a vacuum tube in a horizontal position unless it is made to be so used.

_Don't_ fail to properly insulate the grid and plate leads.

_Don't_ use more than 1/3 of the rated voltage on the filament and on the plate when trying it out for the first time.

_Don't_ fail to use alternating current for heating the filament where this is possible.

_Don't_ fail to use a voltmeter to find the proper temperature of the filament.

_Don't_ expect to get results with a loud speaker when using a single vacuum tube.

_Don't_ fail to protect your vacuum tubes from mechanical shocks and vibration.

_Don't_ fail to cut off the A battery entirely from the filament when you are through receiving.

_Don't_ switch on the A battery current all at once through the filament when you start to receive.

_Don't_ expect to get the best results with a gas-content detector tube without using a potentiometer.

_Don't_ connect a potentiometer across the B battery or it will speedily run down.

_Don't_ expect to get as good results with a single coil tuner as you would with a loose coupler.

_Don't_ expect to get as good results with a two-coil tuner as with one having a third, or _tickler_, coil.

_Don't_ think you have to use a regenerative circuit, that is, one with a tickler coil, to receive with a vacuum tube detector.

_Don't_ think you are the only amateur who is troubled with static.

_Don't_ expect to eliminate interference if the amateurs around you are sending with spark sets.

_Don't_ lay out or a.s.semble your set on a panel first. Connect it up on a board and find out if everything is right.

_Don't_ try to connect up your set without a wiring diagram in front of you.

_Don't_ fail to shield radio frequency amplifiers.

_Don't_ set the axes of the cores of radio frequency transformers in a line. Set them at right angles to each other.

_Don't_ use wire smaller than _No. 14_ for connecting up the various parts.

_Don't_ fail to adjust the B battery after putting in a fresh vacuum tube, as its sensitivity depends largely on the voltage.

_Don't_ fail to properly s.p.a.ce the parts where you use variometers.

_Don't_ fail to put a copper shield between the variometer and the variocoupler.

_Don't_ fail to keep the leads to the vacuum tube as short as possible.

_Don't_ throw your receiving set out of the window if it _howls_. Try placing the audio-frequency transformers farther apart and the cores of them at right angles to each other.