a. Input power transformer T201 receives 115 volts ac, or 230 volts ac
if the instrument is so wired, through the power switch, S1.
The primary
winding of T201 is constructed in such a manner as to utilize either 115
volts ac input, windings parallel, or 230 volts ac, windings in series.
Fuse, F1, protects the Model 845AR circuitry from overloads.
b. The secondary voltage of T201 is rectified by bridge rectifier CR201
through CR204. The bridge rectifier output voltage is filtered by C201 and
regulated by zener CR207.
This regulated output voltage is used as the
operating voltage for the 84 Hz multivibrator.
c. The 84 Hz multivibrator is used to provide synchronous drive
voltages and dc operating voltages for the Model 845AR amplifier circuits
free from any power line frequency variations and harmonics.
The
multivibrator is a transformer-coupled free running multivibrator composed
of transistors Q201 and Q202, transformer T202, and frequency determining
components C203 and R206 through R208.
Variable resistor R206 is used to
adjust the frequency of the multivibrator to 84 Hz.
The voltage at the
secondary of T202 is rectified by CR104 and CR105 to produce the positive
and negative 15 volt dc operating voltages for the amplifier circuits. The
same winding furnishes the synchronous demodulator and isolation converter
drive signals and is tapped at a higher voltage level to drive the neon
lamps DS101 and DS102. These neon lamps provide the drive signal for the
photocell modulators V101 and V102.
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