. Electronic apparatus for biological research . o_ Unstabilized supply in o ? Figure amplifier uses a long-tailed transistor pair, which should reduce the depen- dence of the output voltage on temperature effects. The output characteristic is given as an output resistance of less than 0-04 Q. at zero frequency, and as an impedance, seen looking into the output terminals of the stabilizer, of less than 0-2 Q. at all frequencies up to 100 kc/s, A 5 per cent change in mains voltage produces a 0-2 per cent change in output voltage. The ripple in the output is less than 1 mV, Transistor curr
. Electronic apparatus for biological research . o_ Unstabilized supply in o ? Figure amplifier uses a long-tailed transistor pair, which should reduce the depen- dence of the output voltage on temperature effects. The output characteristic is given as an output resistance of less than 0-04 Q. at zero frequency, and as an impedance, seen looking into the output terminals of the stabilizer, of less than 0-2 Q. at all frequencies up to 100 kc/s, A 5 per cent change in mains voltage produces a 0-2 per cent change in output voltage. The ripple in the output is less than 1 mV, Transistor current stabilizers Power supplies delivering substantially constant currents of up to a few amperes are possible by making use of the very high collector resistance r^ of transistors in the earthed base mode. In Figure the emitter battery ? o- Stabilized current out I -0 + V, -=- /" Unstabilized ~^~* supply in Figure drives a current EfRy into the base, defining a collector current a . {EfRy) which is highly independent of fluctuations in Rj^. The relationship between possible limits of current output, of load resistance, and of input voltage used, may be derived by constructing a working region on the earthed base collector characteristic, and drawing in the load line in the normal manner. Some other transistorized devices A cardiotachometer has been described by Molyneux^*. To achieve a high input resistance the electrodes feed an earthed collector first stage, followed 708
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