Abstract
Various problems on multi-stage amplifiers are treated in the present paper. In the first paragraph, the selective characteristics are explained. That the reactance or the transformer amplifiers whose magnetic circuits are closed ones made of iron sheets have a very good non-seleetive characteristic is because (a) the iron loss flattens the characteristic curve at the resonant frequency, (b) and for frequencies lower than the resonant frequency the effective permeability of the core and hence the plate impedance increase to a certain amount.
In the second paragraph, expressions of the amplification per stage are given for both the selective and the non-selective amplifiers. In the selective type mult-stage amplifiers, the amplification per stage should not be too high. Otherwise amplifiers will have the following disadvantages.
(a) It damages the quality of speech or music for the receptions of wireless telephony. (because of the frequency distortion)
(b) It is liable to start the self oscillation of the system.
(c) It is not suitable for the reception of high-speed telegraphs. By narrowing the amplifying band or increasing the selectivity, the time required forthe curront to built up is proportionally increased.
In the third paragraph problems on the reaction (regenerative) caupling and the amplitude dis ortions are treated. Devices which prevent automatic-ally such distortions in the amplifier system are explained.
In the fourth paragraph the transient phenomena in the amplifiers (when the frequency) is not too high is briefly considered. It is pointed out thatfor the selective type amplifiers this problem is sometimes very important and must be taken into account in the design of such ampliers.
