Philips PM 5125 Manual page 21

25
The constant current source TS28 provides the DC current for TS29
without affecting the AC collector load of the latter. TS28 is also used for
injecting an external synchronising signal into the oscillator loop. This
external signal is applied to the base of TS28 via the coupling capacitor
C37.
The output signal of the oscillator is applied via the emitter followers
TS30 and TS32 to the waveform selector SK2.
The constant current source TS31 together with R49 restore the DC
conditions within the DC feed back loop, without affecting the AC
conditions.
B. SQUARER (See Fig. 28)
The sine wave signal coming from the oscillator and the selector switch
SK2 is applied to the base of the transistor TS61 via the resisror R61.
The transistor TS61 is clamped by means of the diode GR61 in such a
way, that only the negative part of the sine wave signal is applied to the
Schmitt trigger TS62—TS63.
A part of the switched collector current of transistor TS63 is applied
to the potentiometer R2tt, with which the amplitude of the square wave
can be varied continuously.
V
f
R4G+RS
7.7mA
T
1MHz situation
Fig. 10. Thermistor circuit
2mA
T
SKHz situation
RS
~ R61 +R42
R45+RG6
RGG
MA5062