Philips PM 5125 Manual page 23

27
The indication of MI is first adjusted with R105 for the square wave
signal and after that with RI01 for the sine wave signal.
E. STEP ATTENUATOR
The output signal is applied to the terminal BU4 via the step attenuator
consisting of the resistors RI11... R117, the capacitor C90 and the
switch SK4.
The attenuation may be adjusted in steps of 20 dB by means of SK4t
The output impedance is 600 S2 for all positions of SK4.
F. POWER SUPPLY (See Fig. 29)
The a.c. voltages from the transformer TI are rectified by the bridge
circuits GR121 and GR122.
The output d.c. voltages of x-30 V and —30 V are stabilised by comparing
them with a reference voltage (GR127 resp. GR128) via a differential
amplifier (TS128-TS131 resp. TS130-TS132) and by using the difference
to control the current through the series regulator (TS141 resp. TS142),
The amplification of the regulating current is effected by the transistors
TS127 resp. TS129. The current limitation is effected by TS124-8236
and TS126-R237.