Philips PM 5125 Manual page 22

26
From the wiper of R2~i, [he square wave is applied via the emitter
followers TS64-TS65, the capacitors C61-C62 and the selector switch
SK2 to the output terminal BU I, to the step attenuator and to the meter
circuit.
The diodes GR62 and GR63 protect the transistors TS62 and TS63
respectively against high reverse voltages.
The zener diode GR65 limits [he power dissipation of the transistor
TS65. R73 and C69 form a filter against unwanted coupling via the DC
supply lines.
R75 determines the source impedance for TS65 and minimises its
tendency for instability when loaded with a capacitive load.
C63...C66 are decoupling capacitors. C67 and C68 are minor wove
shaping capacitors.
C. AMPLIFIER (See Fig. 28)
The sine wave signal coming from the oscillator and the selector switch
SK2 is applied via capacitor C81 and resistor R81 to the base of the
emitter follower TS82.
From the emitter of TS82, the sine wave signal is applied to the amplifier
TS83. The constant current source TS8l in the collector line of TS83
provides the right DC conditions.
The signal amplified by TS83 is applied to the emitter follower TS84.
A part of the signal present at the emitter of TS84 is fed back to the base
of TS82, which results in an improved band width of the amplifier
(negative feedback).
The signal present at the emitter of TS84 is applied via resistor R94 to
the White emitter follower TS85-TS86. Then the signal is applied via
capacitor C86 and the selector switch SK2 to the output terminal BU 1,
to the step attenuator SK4 and to the meter circuit.
The zener diode GR81 limits the power dissipation of TS84. The capacitor
C84 maintainer the gain in the high end of the required frequency band.
D. METER CIRCUIT (See Fig. 28)
The square wave signal is applied via resistor R104 to the peak detector
GRI01-C101...C103-RIOS...R107. The resulting d.c. voltage is applied
to the meter M1, which monitors the output voltage.
The sine wave signal is applied via the voltage divider 8101 -R102-R103
to the same circuit as the square wave signal.