Chapter 14 



AMPLIFYING REGULATION 



14/1. What is an amplifier? An amplifier, in general, is a device 

 that, if given a little of something, will emit a lot of it. A sound- 

 amplifier, if given a Httle sound (into a microphone) will emit a lot 

 of sound. A power-amplifier, such as the one described in S. 12/21, 

 if given a little power (enough to move L) will emit a lot of power 

 (from H). And a money-amphfier would be a device that, if given 

 a little money, would emit a lot. 



Such devices work by having available a generous reservoir of 

 what is to be emitted, and then using the input to act as controller 

 to the flow from the reservoir. Rarely an amphfier acts by directly 

 magnifying the input, as does the cine-projectionist's lens; but more 

 commonly it works by supplementation. Thus the power-amplifier 

 has some source that will provide power abundantly (the compressed 

 air at A in Fig. 12/21/1), and it is this source that provides most of 

 the power in the output, the input contributing httle or nothing 

 towards the output. Similarly, the work performed by the crane- 

 driver on the control-handle does nothing directly towards lifting 

 the main weight, for the whole of his work is expended in moving 

 electrical or other switch gear. 



It will be seen that in the power amplifier (e.g. that of Fig. 12/21/1) 

 the whole process — that of hfting a heavy weight at H, by a force at 

 L — goes in two stages, by two coupled systems. It is this separation 

 into two stages that makes power-amplification possible, for other- 

 wise, i.e. in one stage, the law of conservation of energy would make 

 any simple and direct amplification of power impossible. Stage 1 

 consists of the movement, by the operator, of the point L against 

 the friction at K and the pressure at V; over this stage energy, or 

 power, is conserved strictly. Stage 2 consists of the movement of 

 compressed air into or out of B and the lifting of P, G and H; over 

 this stage, also, energy is conserved; for the energy used when the 

 weight at // is lifted is derived from the expansion of the compressed 

 air. Thus the whole system can be regarded as composed of two 

 systems, within each of which energy is conserved strictly, and so 

 coupled that forces of 0, 1,2... dynes at L correspond respectively 

 to forces of 0, 1000, 2000, . . . dynes (or some other multiple) at H. 



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