Model 686C Section IV
Paragraph 4- 14
be as close as ossible before a final electrical adjust- full clockwise. See paragraph 4-16 for adjustment
ment is attem ted (see figure 4-9). procedure. Return CATHODE CURRENT control to
setting which gives rated current.
6) Mount the waveguide output flange at the rear of the
front panel. Mount the new current plate on the meter. 18) Check frequency calibration.
7) Reconnect the high-voltage connector and grid
C. FREQUENCY CALIBRATION
connector.
1) Set up test equipment as in figure 4-2. If desired,
8) Recheck the mechanicalpositioning of the bwo tube one wavemeter can be used instead of three.
in the rear. If necessary, readjust the #10 Allen set
screws to accurately center the capsule in the hole. 2) Turn FREQUENCY dial to 8.2 kmc cw output, and
adjust wavemeter to 8.2 kmc. If necessary, adjust
9) Set front panel controls as follows: R132 to make dial setting agree with wavemeter.
CATHODE CURRENT. .... control extreme ccw
3) Turn FREQUENCY dial to 12.4 kmc and set wave-
AMPL. MOD. SELECTOR ........... .OFF
meter to 12.4 kmc. Adjust R135 to bring output fre-
SWEEP SELECTOR ............. RECUR
quency into agreement with the wavemeter.
A FREQUENCY. ................. 140
RF SWEEP RATE. ............... 3.2K
4) Repeat these two checks at 8.2 and 12.4 kmc and
CURRENT SELECTOR ............ CATH.
refine the adjustments.
RF DIAL. ................. 10.0 kmc
RF LEVELER ................. OFF
5) Adjust value of R234 if necessary, to make 10.0
km c track .
10) Refer to Filament Regulator adjustment instruc-
tions in paragraph 4-11. Connect an accurate acvolt-
6) Adjust sweep oscillator to sweep the full band and
meter with an insulated case to the bwo tube filament
set up the three wavemeters at 8.2, 10.3 and 12.4 kmc.
circuit .
Check sweep linearity as described under Sweep Fre-
quency Operation in paragraph 4-5c. If linearity is
11) Turn on power to the sweep oscillator and adjust
not within specifications, refer to paragraph 4-14 RF
the line voltage to 127 volts. Carefully watch the bwo
Sweep Linearity.
filament voltage for 2 minutes. If the voltage exceeds
the rated voltage by more than 0.2 volt, immediately
turn the instrument off and readjust the value of the D. OUTPUT POWER CHECK
padding resistors (figure 4-6).
Check power output across the band as described,
in paragraph 4-5a. Inability to get full power at some
12) After accurately setting the filament voltage at
frequencies or excessive power change vs frequency
127 volts line, reduce the line voltage to 115 volts and
when operating into a matched load is due to a defective
turn off the instrument.
bwo tube. Be certain that an apparent excessivepower
change is not in part due to mismatch in the power
13) Insert two insulated#lO Allen drivers with approxi-
measuring equipment. Critical points in the band
mately 8-inch long handles into the two front positioning
should be checked with a tunable load in the system.
screws.
The @ Model X870A Slide Screw Tuner is recom-
mended for tuning the system.
WARNING
Wrap the shafts with insulating tape to avoid
shorting out adjacent circuitry.
4-14. RF SWEEP LINEARITY.
NOTE: Allow instrument to operate at least 1/2 hour
14) Turn on instrument. After two minutes, adjust
before making adjustments.
CATHODE CURRENT control to obtain 1 ma CATHODE
current .
1) Set up test equipment as in figure 4-2. This pro-
cedure can be performed with one wavemeter. How-
. 15) Rotate CURRENT selector switch to HELIXand ever, when three wavemeters are used, considerable
read the helix current. Adjust the position of the bwo time is saved.
capsule by simultaneously turning the two #10 Allen
screws. Position the tube for minimum helix current. 2) Set the wavemeters to 8.2, 10.3 and 12.4 kmc.
3) Turn the RF SWEEP RATE to 100K.
16) Increase the CATHODE current control until cath-
ode current is value marked on meter plate. Again
-*' 4) Turn the A FREQUENCY to 4.4K.
read helix current andposition tube for minimum cur-
rent. Helix current must always be less than 3 ma
5) Adjust the vernier on horizontal input sensitivity
with CATHODE current adjusted to rated value and at
control of oscilloscope so that the sweep is 8.4 cm.
any output frequency.
6) Adjust R244 (rf sweep linearity) andR246 (rf sweep
17) Adjust dc level R332 to give 1 ma more than rated expansion). See figure 4-16 to obtain a linear display
cathode current with CATHODE CURRENT control set of the full band (8.2 to 12.4 kmc).
4-13
00034- 1 |
ACEC
