MAINTENANCE SECTION 5
MAINTENANCE
5.1. INSPECTION.

5.1.1. GENERAL. - This radio equipment has been constructed of materials considered to be the best obtainable for the purpose and has been carefully inspected and adjusted at the factory to reduce maintenance to a minimum. However, a certain amount of checking and servicing will be necessary to maintain efficient and dependable operation. The following section has been written to aid in checking the equipment.

5.1.2. ROUTlNE INSPECTION. - Routine inspection schedules should be set up for periodic checks of this equipment, This inspection should include examination of the mechanical system for excessive wear or binding and of the electrical system for electrical defects and deterioration of components. If the routine inspection of the equipment is carried out faith- fully, the chances of improper operation of the equipment are greatly minimized. It is suggested that this inspection be made as frequently as possible, and it should be sufficiently thorough to include all major electrical circuits of the equipment as well as of the mechanical portion.

    a. CLEANING. - The greatest enemies of uninterrupted service in equipment of this type are corrosion and dirt. Corrosion, itself, is accelerated by the presence of dust and moisture on the component parts of the assembly. It is impossible to keep moisture out of the equipment in certain localities, but foreign particles and dust can be periodically removed by means of a soft brush and a dry, oil-free jet of air. Remove the dust as often as a perceptible guantity accumulates in any part of the equipment. It is very important that rotating equipment, such as variable condensers and tap switches, be kept free from dust to prevent undue wear, Likewise, variable condenser plates should be kept free from dirt to avoid flashover. One of the greatest sources of trouble in equipment located in a salty atmosphere is corrosion. Corrosion resulting from salt spray or salt-laden atmosphere may cause failure of the equipment for no apparent reason. In general, it will be found that contacts such as tap switches, tube prongs, cable plug connectors, and relay contacts are most affected by corrosion, When it is necessary to operate the equipment in localities subject to such corrosive atmosphere, inspection of wiping contacts, cable plugs, relays, etc., should be made more frequently in order to keep the equipment in good condition.

    b. VACUUM TUBES. - Make a check of emission characteristics of all tubes. After making the emission check, examine the prongs on all tubes to make sure they are free from corrosion. See that all tubes are replaced correctly and fully in their sockets, and that a good electrical contact exists between the tube prong and the socket. Use caution in removing and replacing grid or plate caps on tubes so equipped. Before a tube is discarded, make certain that the tube is at fault and the trouble is not due to a loose or broken connection within the equipment. A complete set of tested tubes of the same type specified should be kept on hand at all times. If faulty operation of the transmitter is observed and tube failure suspected, each tube may be checked by replacing it with a tube known to be in good condition. Defective tubes causing an overload in pover circuits may usually be located by inspection, It will be found that excessive heating or sputtering within the vacuum tubes is a good indication of a fault in the tube circuit. If tubes have been in use for a period of time equal to or exceeding the manufacturer's tube life rating, it is suggested that they be replaced. A marked improvement in the performance of the equipment is usually noticeable after the weak tubes have been replaced.

    c. PRECAUTIONS FOR SATISFACTORY TUBE LIFE.
        (1) Before removing any tube from the equipment, make certain the primary power is disconnected from the equipment.
        (2) Operate all tubes within +/- 5% of rated filament voltage.
        (3) Do not exceed the rated plate current of any tube during normal operation of the equipment.

    d. TUBE REPLACEMENT PRECAUTIONS.
        (1) All tubes are removed by pulling them straight away from the chassis. Some tubes have hold-downs, be sure these are loosened before pulling on these tubes.
        (2) Remove plate cap connectors from tubes with great care to prevent breaking the seal around the plate cap.
        (3) Before inserting a tube make certain it is of the correct type for the socket into which it is to be placed.
            NOTE Changing master oscillator tubes (V001) may cause a slight change in master oscillator calibration.

    e. TUBE TABLE.
 
SYMBOL TYPE FUNCTION RATED FIL.VOLTAGE
V001 6SJ7 Master oscillator 6.3
V101 6AK6 Buffer amplifier 6.3
V102 6AG7 Frequency multiplier 6.3
V103 7C5 Frequency multiplier 6.3
V104 7C5 Frequency multiplier 6.3
V105 4D32 Power Amplifier 6.3
V201  6SL7 Audio Amplifier 6.3
V202 6SN7 Audio driver 6.3
V203  807 Modulator 6.3
V204 807 Modulator 6.3
V30l  5Z4 LV Rectifier 5.0
V302 5R4GY HV Rectifier  5.0
V303 5R4GY HV Rectifier 5.0
V304 VR75 Bias Regulator ---
V305 0A2 Screen Voltage Limiter ---
V306 0A2 Screen Voltage Limiter ---
                      

    f. RELAYS. - All relays should be inspected at regular intervals. Check the contacts for proper alignment, pitting and corrosion. Use a burnishing tool to clean contacts - never use sandpaper or emery cloth.
 

5.2. TROUBLE SHOOTING.

5.2.1. GENERAL. - The most common cause of improper operation of radio equipment is tube failure. Refer to paragraph 5.1.2., b. in this section for comments concerning vacuum tube replacement. Defective tubes causing an overload in power circuits may usually be located by inspection. High voltage arcs may be caused by bent condenser plates, corrosion or dust. Corrosion resulting from operating the equipment in a salt laden atmos- phere may cause failure of the equipment for no apparent reason. In general, trouble encountered in radio apparatus can be isolated by means of various tests and measurements; then the section of the transmitter in which the trouble is located can be determined. If this is done, the components in the associated circuit may be checked and the trouble located. Refer to the tables of meter readings and resistance measurements. No one but an authorized and competent service man equipped with proper test facilities should be permitted to service this equipment.

5.2.2. FUSES.
    a. GENERAL. - This equipment is supplied with fuses of the correct rating in each position. Defective fuses should be replaced by spares only after the circuit in question has been carefully examined to make certain that no permanent fault exists. Always replace a fuse with the rating specified by the following table.

FUSE TABLE
 
SYMBOL LOCATION TYPE RATING
F301 LV Power supply primary Cartridge (3AG) 3 amp.
F302 HV Power supply primary Cartridge (3AG) 5 amp.

   
   


5.3. ALIGNMENT.

5.3.1. GENERAL. - If the exciter stages get out of alignment for any reason, it is recommended that the unit be realigned at once. Improper operation may result in damage to valuable equipment.

5.3·2· HIGH FREQUENCY OSCILLATOR. - Should trouble develop in the high fre- quency master oscillator, the unit should be returned to the factory for servicing. However, the unit can be serviced and realigned by persons under- standing such techniques providing accurate test equipment is at hand. A crystal controlled frequency standard with outputs at 1700 and 2000 kc with an accuracy of better than .015 percent, must be used for setting the band edges.
     a. PROCEDURE.
        (1) Apply power to the transmitter and let the MO warm up for about 30 min. then check the oscillator frequency on a receiver. Operate the transmitter with the emission control in the CAL position and the key closed.
        (2) Couple a receiver to the output of the oscillator.
        (3) Set the vernier index to exact center of the dial window.
        (4) Tune receiver to output of 1700 kc freq. standard.
        (5) Rotate MO to vicinity of 3400 kc on the exciter dial, and zero beat with the signal from the standard. Jot down dial reading for use as a reference.
        (6) Rotate the MO dial toward 4 mc exactly 12 turns.
        (7) Tune the receiver to the 2000 kc output of the standard.
        (8) The MO should zero beat with the 2000 kc output of the standard at exactly 12 turns of the MO dial.
        (9) If such is the case but the dial reading is incorrect, loosen the set screws in the oscillator coupler and turn the dial to the correct reading (4000 kc), after which tighten the set screws again. If the MO does not zero beat with the standard at 4 mc, proceed as follows:

        (10) Read the kc difference (the difference between where the signal appeared and where it should have appeared after 12 turns) and multiply it by 5.

Add this figure to the actual beat note dial setting if the beat note was less than 12 turns or subtract it if the beat note occurred at more than 12 turns.

Now set the dial to this new frequency, remove the trimmer plug from the top of the oscillator, and turn the adjust- ment until zero beat is again reached.

It will be found that the high and low ends are very nearly 12 turns apart.

Repeat the above procedure until such is the case; remember that a new reference point will occur at the low ends of the dial each time.

Examples of above operations:
 Example #1
Beat note at low end of dial = 3402 kc

Reading at which beat note should appear after 12 turns of dial = 4002 kc

Actual dial reading = 4003 kc

Difference frequency (4003 - 4002) 1 kc

Multiplied by 5

5 kc Subtracted from 4003 (since beat note occurred at more than 12 turns) = 3998 kc

After setting dial to 3998 kc and zero beating the MO to the standard with the trimmer
adjustment, the low end beat note should appear at 3398 kc. 

Example #2
Beat note on low end of dial = 3398 kc

Reading at which dial should appear after 12 turns = 3998 kc

Actual dial reading = 3996 kc

Difference frequency (3998 - 3996) = 2 kc

Multiplied by 5 = 10 kc

Added to 3996 (since beat note occurred at less than 12 turns of the dial) = 4006 kc

After setting the dial at 4006 and zero beating the MO to the standard with the trimmer
adjustment the low end beat note should appear at 3406 kc.
 
        (11). After the oscillator has been adjusted to cover the range 3400 to 4000 kc in exactly 12 turns, the coupler set screws can be loosened and the dial set on frequency.
    NOTE: The above method of adjustment is used at the factory. This is a short-cut method and proves very reliable. Actually, the object is to get the 1700 kc and the 2000 kc outputs of the oscillator exactly 12 turns apart. The objective can also be attained by using the slower method of moving the trimmer capacitor in one direction or the other; then checking results until the desired answer is obtained. Be sure to replace the trimmer cover plug after alignment.
    NOTE: Somewhat greater accuracy can be obtained if the oscillator end points are set by using harmonic operation, i.e. listen in the 14 or 28 mc region for the harmonics of the 1700 and 2000 kc signals and set the corresponding harmonic of the MO to zero beat with these. Do this only after obtaining a very close adjustment as outlined above.


5.3.3. MITLTIPLIER STAGES, - Should the grid drive to the final fall below 5 ma on the meter due to change of tubes or aging of components, the transmitter r-f circuits should be realigned. Proceed as outlined below only after the master oscillator has been checked and recalibrated as outlined in paragraph 5.3.2.

    A small fiber screwdriver and a 1/4" open end wrench are required for these adjustments.
 
    a. PROCElDURE.
        (1) Remove the transmitter from the cabinet and tip it up on end. (RF section up.)
        (2) Remove 3 access covers from perforated shield.
        (3) Remove the fuse from the hV primary. (This allows the low voltage supply to be turned on while the W supply remains turned off.)
        (4) Turn the LV and HV power switches Om,
        (5) Place the CW-CAL-PH switch in the PH position.
        (6) Place the METER selector switch in the GRID position.
        (7) Adjust for maximum grid current, using the adjustments and conditions listed below in order from top to bottom of the list. (Refer to figure 5-1 for adjustment identification,)

ORDER OF BAND SW TUNING ADJUSTMENT SET AT SET AT ADJUSTMENT

1-- l0M 28,800 3 Slugs marked "28.8"

2-- 40M 7,300 C150

3-- 40M 7,200 1 Slug marked "7.2"

4-- 15M 21,600 3 Trimmers marked "21,6"

5-- 20M 14,250 3 Trimmers marked "14.4"

6-- 80M 3,750 kc 1 Trimmer marked "3.8"
 
    NOTE: In item 4 under ADJUSTMENT, the mistracking of the third multiplier plate circuit will result in low grid current when the main tuning dial is set much outside the limits of the amateur 20-meter band (14 to 14.4 mc). Proper grid current can be obtained at any frequency on the range 12.8 to 16 mc by adjustment of trimmer C139 (marked 14.4 on the third multiplier.)

    NOTE: If extensive multiplier alignment has been necessary, it is likely that the two spurious signal traps will need tuning, Do not touch the spurious signal tuning condensers unless this is so, since these adjustments are very critical. C149, the spurious signal trap tuning condenser for the 80-meter band, is located on the side of the multiplier unit next to C150, see figure 5-4. These traps are tuned as follows:
    With the transmitter aligned as indicated in the above paragraphs, tune the transmitter for 3.5 mc output and listen with a receiver to the 1.75 mc output. Watching the receiver "S" meter, tune C147 for minimum signal. Then tune the transmitter up on 7.15 mc and listen on 3.575 mc with the receiver. Adjust C149 for minimum signal. Both of these adjustments will be very sharp and care should be taken that they are not disturbed in the least after the adjustments have been made. Replace the multiplier bottom cover.

5.3.4. MODULATOR BIAS ADJUSTMENT. - The modulator bias can be adjusted by turning the screwdriver slot equipped potentioater R305. For best distor- tion characteristics, the static, or resting, modulator platecurrent should be 55 ma with the 600/700 v switch in the 700 v position. Potentiometer R305 is located within the top of the cabinet near the filter capacitors; therefore the interlock switch will have to be held closed while making this adjustment. Take great care to avoid touching any components carrying high voltage. The proper bias for the modulator grids is approximately minus 25 volts.

5.4. LUBRlCATlON. - The following parts should be lubricated annually or whenever the need arises by brushing a thin film of the indicated lubricant on the points of mechanical contact. Don't over-lubricate,
    a. Panel Bushings: MOBILE PD535A (Socony Vacuum Oil Co.)

5·5. OSCILLATOR TUBE REMOVAL. - Replacing an oscillator tube requires the breaking of the seel around the shield and it will then become necessary to reseal the shield. If it becomes necessary to replace an oscillator tube, use a glyptal cement or a generous application of Duco cement to reseal the shield.

5.6. DESICCANT CAPSULE. - A silica-gel tube is mounted on top of the oscillator shield. The silica-gel absorbs moisture from within the oscillator and aids in retaining the oscillator calibration. Moisture causes the color of the silica-gel to change from blue to pink. The silica-gel tube is screwed into a hole in the shield. The plastic tube should be replaced by a new tube of silica-gel when all material within the tube has changed from blue to pink. New tubes of silica-gel may be ordered from the Collins Radio Company.
    NOTE: The seal around the oscillator tube shield and the silica- gel tube is more easily broken if the parts are warm. This can be done safely with a light bulb or infra-red lamp placed close to the oscillator.
  

TYPlCAL TEST VOLTAGES
DC Voltages to Ground measured with Volt-ohmyst.
Conditions: Phone - No Mod. Readings taken at LF end of each band.
V101 6AK6
                 R.F.   

PIN

3.5   
   
 
7.0   
   
 
14.0   
   
 
21.0   
   
 
27.2   
   
 
28.0   
   
 
G1 1 -17 -16.5 -1.0 -0.9 -1.0 -0.9
K  2.7 1.0 1.0 2.9 2.85 2.85 2.9
P  5 235 230 230 225 225 225
G2  6 155 150 65 65 65 65

 
 V102  6AG7
               R.F.   

PIN

3.5   
   
 
7.0   
   
 
14.0   
   
 
21.0   
   
 
27.2   
   
 
28.0   
   
 
K     1,3,5 2.6  2.6  3.9 3.2 3.4 3.2
G1   4 -19 -18 -36 -36 -38 -36
G2   6 215 215 205 205 205 210
P     8 230 230 220 220 225 225
 
 
 V103  7C5
                 R.F.   

PIN

3.5   
   
 
7.0   
   
 
14.0   
   
 
21.0   
   
 
27.2   
   
 
28.0   
   
 
P     2 235 235 215 210 215 215
G2   3
G1   6 -24 -23 -56 -21 -69 -51
K    7 25 25 27 27 26 26

 
V104  7C5
                 R.F.   

PIN

3.5   
   
 
7.0   
   
 
14.0   
   
 
21.0   
   
 
27.2   
   
 
28.0   
   
 
P     2 225 220 215 215 215 215
G2   3
G1   6 -115 -110 -170 -175 -150 -150
K    7 -59 -56 -52 -52 -51 -50

 
V105  RK-4D32
                  R.F.   

PIN

3.5   
   
 
7.0   
   
 
14.0   
   
 
21.0   
   
 
27.2   
   
 
28.0   
   
 
G2    2 285 300 300 300 295 295
K     4,5 0 0 0 0 0 0
G1   6 -120 -100 -93 -105 -105 -102
P     CAP 690 680 690 690 690 690
 
DC Voltages to Ground in Audio System (Volt-ohmyst)
 
 
4D32 Plate Current = 220 MA EP = 700 V      Key Down
 
Key up - key down conditions of V105 (4D32)
Key Up Key Down
Plate E 820 740
Plate I 0 220
Screen E 300 300
f-7 mc
 

Audio Amplifier
V201, 6SL7GT
Pin PH CW
1  G -0.6 -0.8
2  P 88 -0.9
3  K 0 0
4  G 0 0
5  P 100 100
6  K 0.8 0.8
Driver
V202, 6SN7GT
 
Pin PH CW
1  G 0 0
2  P 235 235
3  K 7.4 7.4
4  G 0 0
5  P 235 235
6  K 7.4 7.4
Modulator
V203, & 4, 807
 
Pin PH CW
G2 235 0
G1 -25 -25
K 0 0
P 740 740