drives the voltage comparator Z106 through R116. T h e square wave a t the
output o f Z106 i s limited to +6.2V b y T. C . z e n e r diode CR103. T h e square
wave is then coupled t o the two-section active filter whose operation i s e x -
plained in Paragraph 3 - 4 . above. R 1 3 0 i n t h e second active filter i s used t o
adjust the frequency over a small number o f cycles around the nominal output
frequency. I n i t i a l frequency tuning i s accomplished b y factory-selected trim
capacitors in the two active filters.
3-7. T W O - P H A S E AND THREE-PHASE OSCILLATORS
3-8. I n two-phase and three-phase oscillators, t h e oscillator signal from the
AMPLITUDE control arm in the A -phase power amplifier is buffered b y unity
gain amplifier Z105 and applied to two operational amplifier all-pass phase
shifters, Z103 and Z104. A block diagram o f circuitry used t o generate two-
and three-phase signals i s provided i n Figure 3 - 1 . I n three-phase oscillators,
the B -phase signal lags the A -phase signal b y 120° and the C -phase signal lags
the B -phase signal b y 120°. I n two-phase oscillators the B -phase signal lags
the A -phase signal b y 90° and the C -phase components are omitted. T h e B -
phase and C -phase signals are connected through plug-in connector P2 t o the
12-pin Jones 53I2AB receptacle, J 1 , on the r e a r o f the A -phase power source.
Interconnecting cables then carry these signals t o the B -phase and C -phase
power sources in stacked amplifier systems (see Figure 3 - 2 ) .
3-9. T h e A -phase AMPLITUDE controls acts as a master control t o control the
amplitude o f all three phases simultaneously. W h e n single-phase power ampli-
fiers are stacked f o r two- o r three-phase power, t h e B-phase and C -phase a m -
plitude controls are used only as balance adjustments to set the B -phase and
C-phase outputs equal t o the A -phase output.
3-10. O S C I L L ATO R POWER SUPPLIES
3-11. T h e oscillator circuitry is operated from plus and minus 15VDC regulated
power supplies which a r e derived from the unregulated plus and minus 42VDC
power supplies in the associated power source. - I n the plus 15V power supply,
differential pair Q103 and Q104 compare the plus 15V regulated output t o the
reference voltage from CR102, developing an e r r o r signal t o control compound-
connected pass transistors Q101 a n d Q102. R 1 0 2 , R103, and CR101 ensure that
the regulator starts when power is applied. R 1 0 1 limits the fault current i f the
+15V output is accidentally shorted.
3-12. T h e minus 15V regulator, differential p a i r Q107 and Q108 develop the
error signal b y comparing t h e -15V regulated output to the reg15V.
The error signal is used to control compound-connected pass transistors Q106
and Q107. R 1 0 9 limits the fault current i f the - 1 5 V output is accidentally
shorted.
3-3
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