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b. 50 Ohm SWR Bridge

Standard Milliammeter (400 mA)

d. RF Wattmeter such as R. L. Drake Model WH

or an RF Voltmeter such as Hewlett-Packard

Model 410B or

Boonton Model 91CA.

e. Transmitter with variable output to 100 W CW

at 14 MHz.

50 Ohm Dummy Load

g. 1-1/2 Volt Battery

h. 10 Ohm Potentiometer

Insulated Alignment Tool

5-7.

AMPLIFIER TROUBLESHOOTING

Careful consideration has been given

the design

of the L 7 to keep maintenance problems to a mini-

mum. However, it is quite possible that

someprob-

lem will arise which cannot be solved by tube sub-

stitution. If this occurs, wesuggest that you return

your unit to your dealer, or write directly to

theR.

L. Drake Company, Customer Service Depart-

ment, describing your problem in detail. Include

full information concerning external connections,

control settings, associated equipment and

antenna. Be sure to include the serial number of

the amplifier.

L7 PLATE VOLTAGE

CW-TUNE

1900 Volts at No Load 1760 Volts at

0.565Amps

SSB

2600 Volts at No Load 2400 Volts at

0.800Amps

IDLING PLATE CURRENT

TUBES CWTUNE SSB

Amperex 8802/3-5002 0.100 Amps 0.160 Amos

Amperex 8163

0.100

~mps 0.160 Amis

Eimac 3-4002 0.110 Amps 0.170 Amps

Eimac 3-5002 0.170 Amps 0.260 Amps

All tubes above aredirectly interchangeablein the

L 7 and are capable of operating the full legal limit

for amateur service. All voltages and currents

listed above bear a 10% tolerance for tube and line

voltage variations.

5-8.

TUBE CHECK

A common failure in the final amplifier tubes is a

filament-to-grid short which is usually intermit-

tent. This failure may be detected by theincidence

of negative grid current (and usually some plate

current) during standby. Check each suspect tube

as follows:

a. Observe the WARNING in paragraph

52 and

remove the tubes.

b. Attach an ohmmeter between the grid and

fila-

ment of the tube to be tested. Good tubes will indi-

cate infinite resistance. Bad tubes will indicate a

short circuit. Intermittent tubes will indicate a

momentary short when tapped lightly.

5-9.

ALIGNMENT PROCEDURES

Refer to figures 5-1 and 5-2 as required

locate the

components requiring adjustment.

5-10.

INPUT COIL ADJUSTMENT

The input coils may have to be retuned if the final

amplifier tubes are replaced with a type different

from the tubes removed. Also, they may have to be

retuned if

is desired to operate the amplifier

outside the amateur bands. To retune the input

coils proceed as follows:

a. Disconnect the L7 Power Supply from the

power source.

b. Remove the bottom cover from the Power

Supply.

Remove all of the jumpers from the 7-terminal

barrier strip in the power supply. This allows

the filaments, relay power and blower to

operate without the high voltage being on.

d. Remove the cabinet from the Amplifier. DO

NOT defeat the interlock.

e. Connect the Amplifier

the exciter as for

normal operation EXCEPT: insert a 50 Ohm

SWR bridge in the line (R. L. Drake WH-7 or

eaual).

f. geset the amplifier controls as follows:

BAND: on band to be tuned.

LOAD: fully counterclockwise to zero.

STBY: released (out)

ON-OFF to OFF.

g. Tune the exciter, on CW, to the middle of the

band

tuned.

h. Reconnect the Power Supply to the power

source.

Turn on the L 7 and increase the outaut from

the exciter until the Plate meter reads 0.400

Amperes.

Tune the PLATE control for a dip

plate

current.

Refer

figure 5-1. Turn the slug in the correct

input coil for a minimum reflected power read-

ing on the SWR bridge.

1. Repeat steps f through k for each coil to be

retuned.

NOTE

As shipped from the factory, the input coils

are adjusted for the center of each band and

are broad enough to cover the entire band.

1 2 ... 23 24 25 26 27 28 29 30 31 32 33 ... 36 37

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