Philips PM 5775 Manual page 37

B.3.
B.4.
B.S.
45
Current source, positive pulse out
Fig. VII-6 is a simplified diagram showing the principal function of this circuit.
$4 {S9)
D
NORMAL PULSE OPERATION-MODE
Applied pulse when $4(S9)
is in position-1V and-3V
1 or
1 ot
eeeat
Applied pulse when °Sé (S9)
is in position +1Vand+3V
eae
VS me
When switching over from
negative to positive output, 1 '
the input signal opptied to te
the first amplifier stage
will be inverted vie switch
$4(S9)-2F-2R ~20y
From 2330
Fig. VII-6. Simplified diagram of the current source for the positive output pulse
When switch AMPLITUDE IN 50 Q, S4, is set to positions +1 V or +3 V, the
+20 V supply is connected to the emitters of transistors Z339-Z340. A positive
current I then flows through the transistors to the output at the collector of Z332.
This current will shift the base line in positive direction.
Section 2F-2R of switch S4 at the input of the differential amplifiers (see detailed _
circuit diagram Fig. XIV-8) inverts the pulses so that a positive pulse is obtained
at the output.
FINE amplitude potentiometer RV5 controls current I via Z343. Correct zero
level of the positive pulse is set with potentiometer RV303.
Attenuator
The attenuator consists of a resistive T network R381...R386 which loads the
output of Z332 through two reed relays RE301 and RE302. The network is only
connected in the —1 V and +1 V positions of switch AMPLITUDE IN 50 Q, S4.
At these settings the +20 V supply is connected to the reed relay coils L320 and
L321 which then energize the reed relays so that the attenuating network is
connected to the output line.
DC Offset
Base line shift of 1.5 V both in positive and negative direction is provided by
adding a positive or a negative current to the output pulse.
The positive current is supplied by transistors Z344 and Z345 which are controlled
by potentiometer DC OFFSET IN 50 2, RV4A. Similarly, the negative current is
supplied by transistors Z346 and Z347 which are controlled by potentiometer RV4B.