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Remember too, that excess voltage fed to an amplifier will also produce an excessive heat, which may result in a whole train of minor faults.
Another thing to remember is that no two amplifiers are the same in design, and a wiring-chart is nearly always necessary when carrying out certain repairs. But wiring-charts are often difficult to obtain, and are seldom included in the operators' instructions issued with the equipment. Service engineers are supplied with them as a matter of course, but not operators. Are we to understand from this that the manufacturers do not want you to meddle with the amplifier? (Yes!).
The average operator should concern himself only with the care and actual use of the amplifier. He should know how to clean it properly, how to change valves, and how to adjust the voltage supply correctly, and those are the things which are explained later on.
Never jerk or jar the amplifier. If you do, then you must expect to get an electric shock from it one day. Continual jarring of the equipment will eventually loosen and move some component against the chassis and thus cause the latter to become alive. You will know at once when this happens, and will find some difficulty in carrying on with the show. (The cure will be to earth the projector, and stand on a rubber sheet or thick wooden boards — all very dry). So always handle the equipwith a great amount of care.
Valves
Most amplifier valves deteriorate slowly, and give a certain amount of warning before finally giving out, so if you don't possess a complete set of spares (which you should) you must at once take steps to obtain a replacement. Each valve is numbered, and if, for instance, you find the faulty valve is marked 6J7 then you should ask or write for a 6J7. It is possible, however, to use an alternative, and almost all radio dealers keep a number of books listing them, but alternatives should not be used unless necessary.
Valves are wired either in series or in parallel. (See Fig. 8). Note that in series winding the failure of one will interrupt the circuit and cause the lot to go out, but that if they are wired in parallel you should be able to see which particular valve has
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