Electronic apparatus for biological research Electronic apparatus for biological research . electronicappara00dona Year: 1958 Figure Warning—The anode circuit of power pentode or beam tetrode valves must never be broken whilst the screen potential is applied. If this is done all the cathode current will go to the screen, which is of insufficient thermal capacity to withstand the resulting temperature rise. It is extremely hkely that the screen will melt and the valve be destroyed. Equivalent circuits of valve amplifying stages The voltage gain expression for a simple triode amplifier i,i
Electronic apparatus for biological research Electronic apparatus for biological research . electronicappara00dona Year: 1958 Figure Warning—The anode circuit of power pentode or beam tetrode valves must never be broken whilst the screen potential is applied. If this is done all the cathode current will go to the screen, which is of insufficient thermal capacity to withstand the resulting temperature rise. It is extremely hkely that the screen will melt and the valve be destroyed. Equivalent circuits of valve amplifying stages The voltage gain expression for a simple triode amplifier i,iRl(R + '*«)' suggests the equivalent circuit for the stage introduced in Figure , namely, a pdVg volt generator in series with a resistance /'„, feeding the load Rj^. Similarly, Figure shows an appropriate equivalent circuit for a pentode 9m^K m 'g 'a R. g bVg (a) Figure or beam tetrode stage. Since r„ is usually so much greater than 7?^, its con- tribution to the two resistances in parallel is generally negligible and the valve may be regarded practically as a generator of constant current g^dVy feeding the load Rj^ (Figure ). 148
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