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Power Supplies
The supply voltages used in the 7L5 are -15 V, +5 V,
+15 V, and +35 V. The -15 V supply is decoupled by Q70
to provide the improved ripple rejection needed by the
amplifier. The +15 V supply is decoupled by L82-C82 and
C142, and provides a source for the +5 V supply, R74-
VR74. The +35 V supply is derived by dropping the 7L5's
+50 V source through decoupling resistor R50.
INPUT IMPEDANCE CHANGE
PROCEDURE
The following describes the procedure necessary to
change the input termination of the L3. No provision is
made to change the front panel nomenclature, nor is any
mention made of possible changes necessary in the
calibration procedure.
1. Disassembly of the Unit
a. Remove the L3 from the 7L5, then remove the
screws securing the top and bottom covers.
b. Disconnect the two wires coming from the INPUT
connector to the circuit board. Note their locations for
later replacement.
c. Remove the five screws securing the mother board,
then remove the mother board by carefully prying it
straight out at the front and rear.
2. Changing Input Terminations (R64 and R66)
Replace inputterminating resistors R64 or R66, or both,
as desired. R64should be the larger value of the two unless
they are both less than 300 O. R66 should be less than
6000 and R64 should be less than 900 0 to ensure thatthe
instrument meets its 0.5 dB flatness specification at 5 MHz.
These resistors are located on the mother board, between
relays K62 and K64.
REV. A, OCT 1977
Service Information-L3
4-18
Scans
by
ARTEK MEDIA
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