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.