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SECTION IV
Maintenance


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  1. Press the 30L-1 power switch to ON. Tune and load the 30L-1 into the dummy load. The exciter is now loaded into the 30L-1 circuits. Retune and reload the exciter, if necessary, to 30 watts forward power output.

  2. Watch the wattmeter in the exciter r-f output line, and with a nonmetallic tuning tool, tune L14 for minimum reflected power. Readjust the exciter as necessary to maintain 30 watts forward. Continue adjustment of L14 for minimum vswr (not to exceed 2.0 to 1, or 11 percent reflected power)

  3. Repeat the above procedures at 21.3, 14.3, 7.2, and 3.9 mc, adjusting L15, L16. L17, and L18 respectively.

These adjustments are accessible through the holes in the rear cover of the rear cover. Refer to figure 4 - 1.

For general coverage, use the same procedure as above, except set exciter to a frequency which is in the middle of the desired band. Useful bandwith at the new alignment frequencies is approximately the same as that for the amateur bands. Do not attempt alignment to place the new operating bands outside the ranges listed in table 4-1 for the BAND switch positions indicated. Also do not attempt amateur-band operation on a BAND switch position for which the tuned circuits have been realigned for out-of-band operation.

TABLE 4-1
FREQUENCY COVERAGE ALLOWABLE
BY REALIGNMENT

BAND SWITCH
SETTINGS
LOWER LIMIT
(mc)
UPPER LIMIT
(mc)

.3.5

7.0
14

21

28

3.4

6.5

9.5

16

22

5.0

9.5

16.0

22.0

30.0

4.5 METER LAMP REPLACEMENT.

To replace the meter lamp, remove the bracket to which the socket is fastened. It is held by a small machine screw located at the rear of the meter. Replace the lamp with a type 51 or equivalent.

4.6 TUBE REPLACEMENT.

The tubes may be replaced without removing the r-f compartment top cover and installing new tubes from the top. The following is an alternate method which provides a better access to the tube sockets.

Remove the cabinet, r-f compartment top cover, and bottom cover as outlined in paragraph 4.2 Disconnect plate connectors and remove old tubes. Install the upper pair of replacements from the top of the amplifier. Install the lower pair from the bottom.

 

The locating pin on the base of each of the tubes should point away from the power supply compartment. Attach plate leads, making sure they clear other components. Replace covers and cabinet.



DO NOT BLOCK INTERLOCK SWITCHES. Dangerous voltages are present in this equipment. The high voltage is interlocked with the amplifier covers. Make no attempt to put the amplifier into service until the procedure outlined above has been completed.

4.7 TUNE METER ADJUSMENT.

  1. Make normal connections between exciter and 30L-1.

  2. Connect 50-ohm dummy load to 30L-1 output jack.

  3. Connect vertical input of a wide-band oscilloscope across dummy load.

  4. Connect a two-tone audio oscillator of abot 15 mv rms output to the exciter input.

  5. Using normal procedure, tune and load exciter and amplifier into dummy load at 3.9 mc. Leave 30L-1 METER switch in TUNE position, and remove excitation.

  6. Using USB or LSB emmision, and mon1toring output waveform on the oscilloscope, increase drive until output ceases to increase or peaks begin flatten.

  7. Make fine adjustments to drive level and 30L-1 tuning and loading for maximum output without peak flattening. Output voltage accross dummy load should be not less than 450 volts peak to peak or 160 volts rms, and CW (single tone) plate current should not exceed 700 ma.

  8. Switch exciter to TUNE (approximately 20 watts drive) and adjust C18 with insulating tuning tool to produce reading of zero on 30L-1 multimeter.

4.8 ALC THRESHOLD ADJUSTMEN.

  1. Perform steps a, b, d, and e of paragraph 4.7 Omit step c.

  2. Disconnect alc cable between exciter and 30L-1.

  3. Using USB or LSB emmission, increase driver until indicated alc is about 4 db (S-4) on exciter meter.

  4. Reconnect alc cable, and adjust R16 with insulated tuning tool for 3-db (one S-unit) increase in alc.



Adjustments to tune meter and alc circuits should not be made unless the need has been clearly determined. If trouble is experienced, check PA tubes and exciter first. Improper adjustments can result in damage to amplifier and a distorted output signal. Do not attempt to make adjustments without proper test equipment.


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