HP 608E Operating And Service Manual page 58

Section V Model 608E/F
5-70. To replace Oscillator V6, refer to Figure 5-24
and proceed as follows:
h. Using Model 428 DC Ammeter, measure cur-
rent
in
lead to feed-through capacitor CIS.
1. Set the FREQUENCY RANGE switch to band. E.
Current meter should indicate between 18 and 27
mAo
If
meter indication is not within these limits, substi-
tute another 4042 oscillator tube.
plate current requirements of type 4042 pencil triodes
may diller widely from tube to tube in a given appli-
cation. Therefore, when V6 is replaced, heater volt-
age must be checked and, if necessary, reset to the
proper value; plate current must be held to between 18
and 27 milliamperes by tube selection
~·and
calibra-
tion of the frequency dial must be checked.
)
•
5-73. The crystal-controlled frequency calibrator is
composed ortwo circuits: the 5-MHz crystal-controlled
oscillator, which utilizes the pentode half of a type
6Uatube, and the I-MHz oscillator, utilizing the triode
section of the 6U8. Each section is adjustable, and
both
sections should be adjusted at the same time.
The frequency oUhe crystal can only be adjusted over
a range of approximately 100 Hz. The frequency of
the I-MHz oscillator then locks in with the 5-MHz
frequency and is either right on frequency or is very
far off. To adjust the crystal-controlled calibrator,
refer to paragraph 5-47.
5-72. CRYSTAL OSCILLATOR TUBE OR QUARTZ
CRysrAL REPLACEMENT. To gain access to the
Calibrator Oscillator, remove the side cover on the
RF Generator housing. The entire Crystal Oscillator
is mounted on a bracket on the rear wall of the ampli-
fier compartment. Location of oscillator tube V9,
crystal
Yl,
and. associated adjustments are shown in
Figure 5-27.
If
V9 or Yl is replaced, the calibrator
should be checked and,
if
necessary, adjusted.
5-71. RF AMPLIFIER AfI,'D BUFFER TUBE RE-
PLACEMENT. To remove RF Amplifier VB and Buffer
V22, refer to Figure 5-24 and proceed as follows:
j. USing internal beat-frequency calibrator, check
frequency calibration throughout range of signal gen-
erator, noting points that are significantly
oU
fre-
quency.
k.
To correct calibration
at
the high-frequency
end of all bands simultaneously, adjust t rim mer
capacitor C18 in the 608E, and C59 in the 608F,
which
i8
ac c e
5 5
i b
1
e
in
tube compartment in RF
Generator housing. This adjustment has only minor
effect
at
lOW-frequency ends of all ranges.
Replacement orthe RF Amplifier and Buffer
tubes can affect the amplitude of the RF gen~
erator heater-voltage supply and may limit
the power output from the signal generator.
a. Remove frequency dial and top plate from RF
Generator housing to gain access to tube compartment.
b.
Replace Buffer V22.
c. For Amplifier va, remove socket [rom base of
V8 by straight pull.
d. Remove cathode clip from tube.
e. Using special wrench (located on instrument
'chassis, near RF Generator housing), loosen threaded
retainer ring wbich holds va in housing. Remove re-
tainer ring and neoprene washer.
f. Remove old tube and replace with new type 4043
tube.
g. Check power output throughout full frequency
range of signal generator. With AMPL TRIMMER set
for maximum output at each frequency, a full-scale
reading should be obtained over entire frequency range.
NOTE
""
'un
V20 Vl9 VI8
5 7 ~ 5 "
_ u,..;
'"
.~,
"
Figu.re 5-23. Location of Electron Tubes
" ' /
~.
"'
4''''2
""
.~.
""
~",
a. Remove frequency dial and top plate from RF
Generator housing to gain access to tube compart-
ment. (The frequency dial is accurately indexed on
its hub by two pins to assure exact positioning when
dial is replaced on hub. )
b. Remove socket from base of V6
by
straight pull.
c. Remove cathode clip from tube.
d. Remove the two BH screws holding retainer
plate, then remove plate and fiber spacer.
e. Lift tube gently from hole by straight pull.
f.
Replace tube in reverse order of above steps.
g. Connect a de voltmeter to inside lead of FL4.
Meter should indicate 6.3 Vdc.
If
necessary, change
value of CR20 to obtain 6.3 Vdc.
5-28