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STANDARD WARRANTY (inside front cover)- 1
GENERAL SPECIFlCATIONS--·------------- |
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FRONT PANEL CONTROLS----------------- |
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DESCRIPTION------------------------ |
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INStALLATION INSTRUCTIONS-------------- |
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Unpacking-------------------------- |
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B. |
Tube & Chimney--------------------- |
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c. |
Location--------------------------- |
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D. |
Power |
Requ~rements----------------- |
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Jumper |
Connection Diagrams--~------ |
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F. |
Low Pass Filter-------------------- |
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Antenna Requirements--------------- |
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H. |
Ground Requirements---------------- |
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I. |
Exciter Requirements--------------- |
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J. |
Transmitting AGC------------------- |
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K. |
VOX Relay-------------------------- |
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L. |
Initial Connection Diagrams-------- |
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M. |
Viewing Angle Options-------------- |
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TUNING PROCEDURE----------- |
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CW & RTTY-------------------------- |
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B. |
88B & AM--------------------------- |
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OPERATION------------------------------ |
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A. |
CW & RTTY-------------------------- |
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B. |
8SB------------- |
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c. |
AM--------------------------------- |
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D. |
SWR Calculation-------------------- |
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E. |
Accessory Frequencies-------------- |
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THEORY OF OPERATION-------------------- |
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SERVICE DA~-------------- |
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Amplifier-------------------------- |
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Power Supply----------------------- |
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Ordering Service Parts------------- |
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Returning L..4Bto Pactory----------- |
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ALIGNMBNT------------------------------ |
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Input Cotl Adjuatment-------------- |
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Meter Adjuatment------------------- |
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Knob Pointer Alignment------------- |
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Wattmeter Calibration-------------- |
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SCHEMATICS for L-4B Amplifier and Power Supply (lalt 2 fold out pagel) .
gENERAL SPECIFICATIONS
FREQUENCY COVERAGE - Ham bands 80 through 10 meters. All frequencies 3.5 to
30 MHz may be covered with some alteration of input circuit.
PlATE INPUT - 2000 watts PEP - SSB, 1000 watts OC on CW, AM and RTrY.
DRIVE REQUIREMENTS - 100 watts PEP - SSB, 7S watts ~W, AM and RTTY.
INPUT IMPEDANCE ... 50 ohms.
OUTPUT IMPEDANCE - Adjustable pi-network matches 50 ohm Une with SWR not to exoeed 2:1.
INTERMODUIATION DISTORTION PRODUCTS - In excess of -33 DB
WATTMETER ACCURACY'" 300 watts forward and reflected, .±. (5% of reading
+ 3 watts). 3000 watts forward, ± (5% of reading + 30 watts).
POWER REQUIREMENTS - 230 volts 50 - 60 cycles 15 amperes, or 115 volts 50
60 cycles 30 amperes.
DIMENSIONS - Amplifier 13-1S/16'· W x 7-1/S" H x 14-5/16" OJ Power Supply 6-3/4· W x 7-7/8" H x II'· D.
WEIGHT ... Amplifier 32 Ibs; Power Supply 43 lbs.
TUBE COMPLEMENT - Two 3-S00Z or Two 8802/3-S00Z or Two 8163 or Two 3-400Z.
FRONT PANEL CONTROLS
ON-OFF ... Rocker SWitch
SSB-CW/l'UNE - Rocker SWitch changes plate voltage for different modes of oper ation.
BA.ND - Switch selects desired ham bands (See Frequency Coverage) •
PIATE and LOAD ... Tuning adjust pi*-network capacitors in tank circuit for proper resonance and loading on all bands.
METER - Switch selects monitoring either grid current. plate voltage, forward or reflected RF power on the lower meter.
AGe/STANDBY PUSH ... Transmitting AGe threshold adjustment and push-pull switch that allows the L-48 to remain on while operating with the exciter only.
RFAR JACKS - Power (connects L-4B to power supply), high voltage, VOX (for tum ing on L-48 with exciter VOX contacts), transmitting AGe (for connecting trans mitting AGe to exciter), RF input (for connecting to exciter RF output), RF output (for connecting to an antenna) •
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ME'lERS - Plate Current, Grid Current/Plate Voltage/Forward Power/Reflected
Power (switch selected>.
POWER SUPPLY controls - Two circuit breaker reset buttons.
DESCRIPl'ION
The R L DRAKE Model L-4B Linear Amplifier offers continuous 2000 watts PEP ssa, and 1000 watt DC. CW, AM and RTTY operation covering the ham bands 80
through 10 meters. All frequencies 3.5 to 30 MHz may be covered with some re alteration of the input circUit.
The L-4B uses two 3-S00Z or two 8802/3-S00Z or two 8163 or two 3-400Z zero bias triodes in a Class B grounded grid circuit configuration that utilizes RF negative feedback for lower odd order distortion products.
A transmitting AGe circuit controls the exciter gain to allow the highest average power without peak clipping. An internal changeover relay feeds the antenna through when the L-4B is turned off. A pair of relay contacts bias the output tubes to cutoff, eliminating unwanted heat and diode noise when receiving.
The output tubes are forced-air cooled by a. very quiet low velocity, high volume internal blower. Two taut-band suspension meters indicate plate current, grid current, plate voltage, and relative RF output power.
The separate solid state power supply requires no warm up period and provides excellent dynamic and static voltage regulation.
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Do not turn on the L-4 |
amplifier with the top cover removed because the high voltage interlock shorts out the 8 + and will damage power supply components.
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INSTALlATION INSTRUCTIONS
The L-4B has been designed incorporating several1nter-Iocks to prevent danger ous electrical shock. However, it Is possible to disconnect the high voltage ter minal while the L-4B Is turned on. This Is a potentially dangerous situation and should never be attempted for any reason. When disassembling the L-4B, the high voltage terminal should be disconnected last and upon reassembly the high volt age terminal should be connected first. The L-4B and its power supply can be installed and serviced in complete safety if the instructions in this manual are ·followed expl1citly•
A o UNPACKING
Carefully remove your L-4B Amplifier, tubes and chimneys, and power supply from their packing cartons and examine them closely for signs of shipping damage. Should any damage be apparent, notify the delivering carrier immediately, stating the full extent of the damage.
Fill out and mail the enclosed registration qard so that your warranty -will be effec tive o
Save the packing material, you may need 'it later for reshipment or storage.
Inspect the packing material closely before putting it away to be sure you have not overlooked the cables or other hardware shipped with the
Bo TUBE AND CffiMNEY INSTALlATION
Tubes and chimneys can be installed after removing the top cover (see Service Data, Amplifier, Removing Top Cover) •
The tubes are installed first o Notice that base Pin 3, the pin with no immediately adjacent pins, face In either SOCket, the ends of the amplifier case. When instal ling the tubes, push straight down to insert them and do not rock the tubes or the base pins may break.
The chimneys are installed after the tubes and extra care ~ust be exercised while handling them because they are fragile. The chimneys should be installed by
. pushing t~,yo clips outward with the chimney until the opposite clips will be cleared when the chimney is lowered onto the chassis. Check to be sure that both chimneys are flush with the chassis and that no clips are inside of the chim neys. The parasitic chokes are installed after the tubes and chimneys. Remove the screw at the top of the pla~ connector and use this screw to fasten the para
sitic choke to the plate connector. The parasitic choke coil should hang down
!!!!.S! from the supporting leads. The free ends of both parasitic chokes can then be connected to the top of the plate RF choke with the 1/4 - 20 round head alu minum machine screw already in the top of the plate choke. Do not overtighten this screw when connecting the parasitic chokes: a snug fit is adequate. After replacing the top cover, the amplifier can be connected for operation.
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c. LOCATION
In general, the location of the L-4B is not critical, however, there are certain considerations which must be given to insure optimum performance. Care should be taken to insure that space is allowed around the amplifier and power supply cases to allow adequate air circulation. Extremely hot locations, such as near radiators or heating units should be avoided. Do not cover the tops of the ampli fier or power supply cases with books, papers or other pieces or equipment or overheating may result o The back of the amplifier case must not be obstructed and should not be placed closer than 1 inch from a wall or the air inlet for the blower will be blocked and overheating of the ampUfier tubes may occur.
D.POWER REQUIREMENTS
The L-4B is included with its own separate power supply which can be operated from either 115 VAC or 230 VAC SO - 60 cycles. Because of the large variety of plug and socket configurations _for 230 volt service, and because the L-4B can be operated from either 115 volts or 230 volts, a line plug is not furnished with the L-4B. The L-4B is shipped from the factory with jumpers connected to operate on 230 VAC 0 It 1s highly recommended that the L-4B be operated from its own 230
volt 15 amp or greater, circuit. If a 115 V circuit Is all that is available, it should be fused for 30 amps and the circuit conductors should not be less than il0 and no other equipment should be operated from this circuit. Do not under any circum" stances operate the L-4B from a 115 volt lighting circuit because the circuit con ductors are not large enough to safely carry this load.
E.JUMPER CONNECTION DIAGRAMS
Below are pictorials of jumper connections for both 230 V and 115 V operation. The jumpers in both the amplifier and power supply must be connected as shown or serious damage to the L-4B components may result.
115 VOLT OPERATION
Amplifier |
Power Supply |
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230 VOLT OPERATION
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Amplifier |
Power Supply |
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F• LOW PASS FILTER
The L-48 has been designed in accordance with good engineering practices and second harmonic content Is attenuated from the fundamental by at least 35 dB. Because of the posSibiUty that you may be using a multiband antenna or have a feed line that is resonant at a harmonic frequency, it is highly recommended that
asuitable low pass filter such as our Model TV-IOOO-LP be used with the L-4B.
G. ANTENNA REQUIREMENTS
The L-48 has been designed for use With antennas resonant at the operating fre quency and having approximate impedances Within the limits of 25 to 100 ohms.
The nominal output impedance of the L-4B is 50 ohms and the SWR of this load should never exceed 2:1. Although there are many types of antennas which will meet these requirements, the simplest is a one-half (1/2) wave dipole center fed With S~ ohm coax. For a detailed discussion on antennas, we suggest referring to an appropriate antenna book.
Most practical.antennas exhibit an SWR range over a complete amateur band that exceeds 2:1. For this reason we recommend using an antenna matching network such as our MN-2000 which will allow the L-48 to work into a 50 ohm load for maximum power transfer into the antenna.
CAUTION: NEVER ATTEMPT TO OPERATE THE L--48 WITHOUT FIRST CON NEcTING IT TO AN ANTENNA OR 50 OHM DUMMY LOAD OF
SUFFICIENT POWER HANDLING CAPACITY OR SERIOUS DAMAGE
MAY RESULT.
H.GROUND REQUIREMENTS
The L-4B should be attached to a good earth ground through as short and as large a ground strap as possible for best results. A binding post is provided on the
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rear of the L-4B chassis for this purpose.
It Is always a good idea to connect the chassis' of-all associated equipment to gether and ground them at one point to avoid ground loops. We recommend that
all of the equipment in your station be connected together and grounded at the L-48 amplifier chassis.
I.EXCITER REoUIREMENTS
To operate the L-48 at the maximum legallnput, it will be required of the exciter to deliver to the L-48 input connector, 100 watts PEP-SSB RP power and 15 watts RP power on CW, AM RrTYand TUNE. The TR-3, TR-4. r-4/r-4X/l'-4XB Trans mitters all have adequate power to drive the L-4B to
allowed on 8SB, CW. Rl'T~ and AM. The exciter should be placed as close to the L-48 amplifier as practical so that the coax and ground strap will be short.
J• TRANSMITTING AGe
A jack on the rear of the L-48 amplifier is proVided for connection to the exciter of a transmitting AGe voltage which controls the gain of the exciter so that any power level can be run up to 2000 watts PEP without peak clipping•.The L-48 is supplied with a cable to connect this jack to a similar jack on our Model AC-4 Power Supply which terminates in the particular transmitter the AC-4 is powering.
A connector is available for AC-3 Power Supplies that brings out the vox c·ontacts and a transmitting AGe connector from the transmitter that the AC-3 is powering.
K.VOX RElAY
A two pin Jack on the rear of the L-48 amplifier Is prOVided for connection to a pair of nonnally open relay contacts in the exciter which close on transmit and thus tum on the L-4B at the same time. The L-4B is supplied with a cable to connect this Jack to a similar Jack on our Model AC-4 Power Supply which termin ates in the particular transmitter the AC-4 is powering.
Some exciters (except TR-3, TR-4. T-4/r-4X/1':"4XB) ground one of the extra relay contacts made available to key a linear amplifier. For these exciters it will be necessary to plug the two pin connector tnto the L-48 vox socket in the correct
. position. With the exciter 1n standby, if plugging in the vox connector causes the L-48 plate current to read up scale, reverse the vox connector 1n its socket so that the" plate current Is zero.
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INITIAL CONNECTION DIAGRAMS
L-48
T.....3141 T-41T-4X/T-4)(8
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fiG. I CONNECTING THE TR-3/TR-4/T-4/T"4. AND AC-4 TO THE L48 UNEAR AUPUFIER
L-48 |
L-4PS |
<t •
.... AGe e.....
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