DRAKE L7 User manual
OPERATOR'S MANUAL
LINEAR AMPLIFIER
0
R.
L.
DRAKE COMPANY
1979
PRINTED
IN
U.S.A.
TABLE
OF
CONTENTS
..
-~
.
PAGE
...................................
...................
CHAPTER
1
INTRODUCTION
,
1-1
...............................................
1-1 GENERAL DESCRIPTION 1-1
..................................................
1.2
.
MANUALCOVERAGE 1-1
........................................................
CHAPTER
2
INSTALLATION 2-1
2.1 . UNPACKING
...........................................................
2-1
..................................................
2.2 . TUBE INSTALLATION 2-1
2.3
.
LOCATION
.............................................................
2-1
...............................................
2.4
.
POWER REQUIREMENTS 2-2
...............................................
2.5 . JUMPER CONNECTIONS 2-2
............................................
2.6 . ANTENNA REQUIREMENTS 2-2
.....................................................
2.7 . LOW PASS FILTER 2-2
.................................................
2.8 . MATCHING NETWORK 2-2
.............................................
2.9
.
GROUND REQUIREMENTS 2-2
..............................................
2-1
0
.
EXCITER REQUIREMENTS 2-2
..................................................
2-1
1
. TRANSMITTING AGC 2-2
.......................................................
..
2-1
2
. VOX RELAY .-. 2-3
r
-
4PTER
3
OPERATION
...........................................................
3-1
..............................................................
3.1 . GENERAL 3-1
.................................................
3.2
.
TUNING PROCEDURE 3-1
3.3
.
CW AND RTTY TUNING
................................................
3-1
3.4
.
SSB AND AM TUNING
.................................................
3-1
3.5 . OPERATION ........................................................... 3-3
............................................
3.6.' CW AND RTTY OPERATION 3-3
.......................................................
3.7
.
SSB OPERATION 3-3
.......................................................
3.8 . AM OPERATION 3-3
...................................................
3.9 . SWR CALCULATION 3-3
3-1
0
. OPERATION ON ACCESSORY FREQUENCIES
..........................
3-4
...............................................
CHAPTER
4
THEORY OF OPERATION 4-1
4.1 . INPUT
.................................................................
4-1
..................................................
4.2 . TRANSMITTING AGC 4-1
...............................................
43
.
STANDBY CUTOFF BIAS 4-1
4.4
.
OUTPUT
...............................................................
4-1
4.5
.
WATTMETER........................................................... 4-1
........................................................
CHAPTER
5
MAINTENANCE 5-1
.........................................................
5.1
.
SERVICE DATA 5-1
.....................................................
5.2
.
PARTS ORDERING 5-1
.............................................
5.3
.
AMPLIFIER DISASSEMBLY 5-1
.............................................................
5.4 . CLEANING 5-1
PAGE
....
TUBE REPLACEMENT..
..............................
5-1
..............
TEST EQUIPMENT
...................................
5-1
AMPLIFIER TROUBLESHOOTING
...................................
5-2
.................
TUBE CHECK..
..................................
5-2
...
ALIGNMENT PROCEDURES..
,
...................................
5-2
INPUT COIL ADJUSTME
..................................
5-3
METER ADJUSTMENT
......
.......................................
5-3
WATTMETER CALIBRATION,
............................
...
.......
5-3
............
NULL ADJUSTMENT
..................................
5-3
300 WATTS REFLECTED
...............................................
5-3
300 WATTS FORWARD
..................................................
5-3
3000 WATTS FORWARD
................................................
5-4
KNOB POINTER ALIGNMENT
..........................................
5-4
POWER SUPPLY CIRCUIT BREAKER RESET..
..........................
5-4
REMOVING THE BOTTOM COVER
.....................................
5-4
REMOVINGTOP COVER
...............................................
5-4
POWER SUPPLY TROUBLESHOOTING
.................................
5-4
LIST
OF
ILLUSTRATION'S
Figure
1-1
2-1
Page
--
i
i
.
.
MODEL L7 LINEAR AMPLIFIER
..................................
1-2
:'-
.z.
REAR CHASSIS CONNECTORS
..................................
2-4
5-'
JUMPER CONNECTIONS FOR 120 VOLT OPERATION..
...........
2-5
:'
JUMPER CONNECTIONS FOR 240 VOLT OPERATION..
...........
2-5
,
CONNECTINGTHE PS-7 POWER SUPPLY AND THE
R.
L.
DRAKE LINE OF COMPATIBLE EXCITERS
......................
2-6
......................................
VIEWING ANGLE OPTIONS 2-7
...............
....................
FRONT PANEL CONTROLS
L..
3-2
PLATE VOLTAGE AND PLATE CURRENT VS 1,000 WATTS
.............................................
DC INPUT POWER 3-5
..............................................
SWR NOMOGRAPH
3-5
..........................
COMPONENT LOCATIONS,TOP VIEW.. 5-5
.....................
COMPONENT LOCATIONS, BOTTOM VIEW.. 5-6
CONNECTIONS FOR GRID CURRENT METER
....
--
-
..->.r
..
~;
-
-
..
.....
..........................................
CALIBRATION
.,
5-7
............
MODEL L7 POWER SUPPLY SCHEMATIC DIAGRAM.. 5-7
.........
MODEL L7 LINEAR AMPLIFIER SCHEMATIC DIAGRAM.. 5-9
1-1.
GENERAL DESCRIPTION
TheR
L.
DrakeModelL
7
LinearAmplifieroffers
con.tinuoas 2000 Watts PEP on SSB, and 1000
Watts
DC
on CW,
AM
(controlled carrier) and
RTFY
operation covering the ham bands 160
through
15
meters. Non-amateur frequencies
between
1.8
and
21.5
MHz
may be covered with
mdi5cation of theinput circuit.
The
L7
uses
2
zero-bias triodes in a Class
B
gmunded-grid circuit configuration that utilizes
RF
negative feedback for lower odd-orderdistor-
tion products.
As
shipped from the factory,these
tubes
will
be
one of the following listed parts,
which
are interchangeable but which are fur-
nished
in
pairs only:
Amperex 8802/3
-
5002
Amperex
8163
Eimae
3
-
4002
Eimac 3
-
5002
The
tnbes
arecooled by a quiet, dual-speedinter-
nal
&we.
A
transmitting AGC circuit controls the exciter
gain
to
allowthe highest average power without
peak
clipping.Aninternal changeoverrelay feeds
CHAPTER
1
INTRODUCTION
theantennathroughwhentheL
7
is
turnedoff.A
pair of relaycontactsbiastheoutputtubes
to
cut-
off, eliminating unwanted
heat
and diode noise
whenreceiving. Twometersindicateplatecurrent,
grid current, plate voltage,
RF
output power, and
RFreflectedpower. TheseparatesolidstatePower
Supply requires no warm-up
period
andprovides
excellent dynamic and static vol-e regulation.
1-2.
MANUAL COVERAGE
This manual
is
presented
in
5
chapterswith sup-
porting illustrations andis arranged for thecon-
venience of theoperatorand
service
technicianas
follows:
Chapter
1
Introduction (self explanatory).
Chapter
2
Installation. Describestheprocedure8
to
be followed prior
to
operation.
Chapter
3
Operation. Illustrates and describes
front panel controls and describes
tune-up and operation
in
SSB, CW,
RTTY, TUNE and
AM
modes.
Chapter
4
Theory of Operation. Describes all
critical circuits and networks.
Chapter
5
Maintenance. Provides maintenance
instructions, troubleshooting and
parts orderinginformation.
'
Fig.
1-1
Model
L7
Linear
Amplifier
6
.>-
SPECIFICATIONS
Frequency Coverage: Hambands
160
through
15
meters. Non-amateur
fre-
quencies between
1.8
and
21.5
MHz may be covered
with some modification of
the input circuit.
Plate Input:
2000
Watts PEP on SSB
and
1000
Watts DC on CW,
AM
andRlTY.
Drive Requirements:
100
Watts PEP onSSBand
75
Watts on CW,
AM
and
nmr
IbLLI.
Input Impedance:
50
Ohms(BandPassTuned
Input),
Output Impedance: Adjustable pi-network
-
matches
50
ohm line with
SWR not
to
exceed
25.
Intermodulation
'
'
DistortionProducts In excess of
-33
dB.
WattmeterAccuracy:
300
Watts forward and re
flected,
*
(5%
of reading
+
3
Watts).
3000
Wattsforward,
*
(5%
of reading
+
30
Watts).
Power Requirements:
240
Volts
50-60
Hertz
15
Amperes,or
120
Volts
50-60
Hertz
30
Amveres.
Tube Complement: Two of
3-5062
or
8802/3-
.5002
or
8163
or
3-4002.
-
-
.
-
- - -
Dimensions: Amplifier
1*11/6
in. W x
6-3/4
in. H
x
14-1/4
in. D.
(34.8
cm W
x
17.1
cm H x
36.2
cm D.)
PowerSupply
6-3/4
in.
w
x
7-7/8
in.H
x
11
in.
D.
(17
cm
.
Wx20cmHx28cmD.)
Weight: Amplifier
-
27
lbs.
(12.25
kg.)
Power Supply
-
42.5
lbs.
Q9.3
kg.)
*
Exportmodelincludescoverageof
10
meterHam
Band.
WARNING
The
L
7
hasbeen designedincorporatingseveral
interlocksto preventdangerouselectricalshock.
However,
it
is possible to disconnect the high
voltageterminal while the
L
7
isturned on.This
is
EXTREMELY DANGEROUS
and never
should be attempted for amreason. When dis-
assembling the
L
7,
the high voltage terminal
should
be
disconnected
LAST
andatreassembly
the high voltage terminal should be connected
FIRST.
The
L
7
and its Power Supply can be
installed and servicedin complete safety
if
the
instructions in this manual are followed ex-
plicitly.
''
2-1.
UNPACKING
The
L
7
Linear Amplifierisshipped from thefac-
tory
in
3
separatecartone;
1
contains the Ampli-
fier,
1
contains the Power Supply and the third
contains the tubes and the miscellaneous hard-
ware.
Carefully unpack all three cartons and
examine
their contents for evidence of shipping
damage. If any damage
is
discovered, notify the
transportation company that delivered the
equip-
ment.
Be
sure to keep the cartons and packing
material
as
thetransportationcompany
will
want
to examine them. Keep the carton and packing
even
if
no shipping damage occurs. Having the
original cartups available simplifies repacking
the equipment for storage or to return
it
to the
factory for service. Inspect the packing material
closelybefore storing
it
tobesurethatnoneof the
accessoryhardwarehasbeen overlooked. Thedis-
mounted components and accessory hardware
shipped
with
the
L
7
should be checked against
thefollowinglist.
a. 2 tubes (Amplifier
V1
and V2)
b
.
2
Plate Caps (forTubes)
c. (2)632x518 screws (for Plate Caps)
d
.
2
Parasitic Chokes (NoteTOPlabel)
e.
(2)
6432x114 Screws (connect Chokes to Caps)
f.
2
Internal Tooth Lock Washm (connect
Chokes
to
Caps)
g
.
2
Cables (1Vox Relay,
1
Transmit
AGC)
h.
1
Plug,
%Pin
(Vox Relay)
i.
2 Resistors, 0.82 Ohm,
2
Watts (&placement
sparesfor Power Supply
R12)
j
.
2
RubberFeet (ForViewingOptionB)
k.
2
studs (toattachrubber feet)
CHAPTER
2
INSTALLATION
1
.
1
Instruction
Manna1
(READ
ZF)
m.
1
Warranty F&gi&ration
Card
Nrn
EFll
out the enclosed
Warranty
Regidrdon
card
and
return
it
tothe
~ryhnediately
to
insue
-tion
andvalidation
of
the
warran*.
2-2.
TUBE INSTALLATION
WARNING
Tubes
must
beMed
andthecabinetreplad
BEFORE
ANY
CO~ONS
are
made
to
the
L
7.
a. Remove the
6
screws
which
secure
thecabinet
to the amplifier andremove
the
cabinet
b. Refer to fignre+L
Insert
both
tobes
into
the
sockets on the amplifier
ehassia
Note the pin
arrangement:
Pin
3
is
isola6ed.
c.
Install
the
plate
caps
on the
tubes
andsecure
them
with
the scsewsprovided.
d. Attachtheparasiticchokestothetopofeachof
theplate
caps
with
the
screws
and
loekwashers
provided. Make
sure
thatthe
coils
of the two
chokes hang
DOWN.
The
word
TOP
stamped
on each choke musk
be
visible from thetop of
the amplifier.
e. Attachboth of theremainingleadsonthepara-
sitic chokes
to
the top
of
the
plate
RF
choke
using the
1/420
alnmmmn
screw
which
also
securesonelead from thecouplingcapacitors.
DO
NOT
wertighten this screw.
f.
Replace the cabinet and
secure
it
with the
6
screws removed
in
step
a
2-3.
LOCATION
In
general, the location of the
L
7
is
not Critical;
however, there are
certain
considerations which
must be
given
to
insure optimum performance.
Care should be taken toinsurethata spaceispro-
vided around thePower Supply casetoallowade
quate air circulation. Extremely hot
locations,
suchasnearradiators orheating
units,
shouldbe
avoided. 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
theblower
will
be blocked and overheating of the
tubes may occur.
2-4. POWER REQUIREMENTS
The L 7is furnished with its own separatePower
Supply which can be operated from either 120
VAC or240 VAC 50-60Hertz. Becauseof thelarge
variety of plug and socket configurations for 240
volt service, and because the L 7can be operated
fromeither 120Voltsor240Volts,alineplugisnot
furnished with theL
7.
TheL 7isshippedfromthe
factory with jumpers connected to operateon 240
VAC. It is highly recommended that the L
7
be
operated from its own 240 Volts (15 Amps or
greater) circuit. If a 120 Volt circuit is all that is
available, it should be fused for 30 Amps andthe
circuit conductors should not be less than No. 10.
No other equipment should be operatedfrom this
circuit. DO NOT under anycircumstancesoperate
theL 7from a 120Voltlightingcircuitbecausethe
circuit conductors are not large enough to carry
this load safely.
2-5. JUMPER CONNECTIONS
Figures 2-2 and 2-3 are diagrams of jumper con-
nections required for 120 and 240 Volt operation.
The jumpers in both the Amplifier and Power
Supply must be connected as shown or serious
damage to the
L
7
componentsmay result.
2-6. ANTENNA REQUIREMENTS
The L 7has been designed for use with antennas
resonant at the operating frequency and having
approximateimpedanceswithin thelimits of 25to
100 Ohms. T)le nominal output impedanceof the
amplifier is 50 Ohms and the SWR of this load
shouldnever exceed 23.Although there aremany
types of antennas which will meet these require-
ments, the simplest is a one-half wave dipole
center fed with 52 Ohm coax. For a detailed dis-
cussion on antennas, refer to an appropriate
antenna book.
2-7.
LOW PASS FILTER
The amplifier has been designed in accordance
with good engineering practices, and harmonic
attenuation meets or exceeds current FCCspecifi-
cations. Becauseof thepossibilitythatyou maybe
qsinga multiband antennaorhave afeedlinethat
isresonant at a harmonic frequency,itis highly
recommended that a suitablelow pass filter such
asthe
R.
L. DrakeModel TV-3300- be used with
the
L
7.
2-8. MATCHING NETWORK
Most practical antennas exhibit an SWR range
over a complete amateur band that exceeds 2:l.
For this reason we recommend using anantenna
matching network such as the R.
L.
Drake
MN-
2700 which will allow the L 7 to work into a 50
Ohm
load for maximum power transfer into the
antenna.
CAUTION
Never attemptto operatethe
L
7
withoutfirst
connectingto anantennaor50 OhmDummy
Load of sufficient power handling capacity
or serious damage may result.
2-9. GROUND REQUIREMENTS
For best results, the amplifiershould be attached
to a good earth ground through as short and as
largea ground strapaspossible.Abindingpostis
provided on the rear of the amplifier chassis for
the ground connection.Itis always a good ideato
connect the chassis of all associated equipment
together
and
ground them at one point to avoid
groundloops.We recommendthat allof theequip-
ment in your station be connected together and
grounded atthe L
7
Amplifier chassis.
2-10. EXCITER REQUIREMENTS
To operate the amplifier at the maximum legal
input the exciter must provide 100Watts PEPRF
power for SSB operation and
75
Watts RFpower
for CW,
AM,
RTTY and TUNE operation.
Locate the exciter as close to the amplifier as
practical
to
shorten the coaxialcableandground
strap.Refertofigures2-4 and 2-5 for recom-
mended connection arrangements.
2-11. TRANSMITTING AGC
ThetransmittingAGC voltage,whichcontrolsthe
gain of the exciter, is presented at a connector
labeled XMTG AGC OUTPUT on the rear of the
L
7.
Any power level canbe run up to 2000 Watts
PEP without peak cliGping. A cable is furnished
with the amplifier which provides a connection
to the
R.
L.
DrakePS-7
or AC-4Power
Supply.This
connection
is
routed through thepower supplyto
the transmitter.
2-12.
VOX
RELAY
Aphonojack on therearoftheL7AmpMerkpm
vided for connection to a
paiT
of norma&
open
relay contactsin theexciter,
which
doseontrans
mit and thus turn on the arnpliik
ar
the
same
time The L7 is supplied
with
a
cable
with
phom,
plugs on each endfor
this
pnrpase
AGcand-
PS7Power Supplies
are
equipped
ui+h
a
-'pin
connector instead of a phono
jackforthis-
tion. A loose two pin plug
is
soppH
ssith
tbeC
accessory kit and
this
plug
must
be
ix&dkd
cm
one end of the cable
in
place
of
the
phmo
when used with
these
models.
For TR7's and
similar
excbs.
ir
is
w
observe the
correct
polar&
when
tealhe
VOX
RELAY
circuit
If
a
phono
conneebris
aed
this is automaticall3 ammpldud
If
a
tro
pin
connector
is
used.
the
wrred
polarity
is
obginsd
with the folloaiing
pdm
Place
rbe
&in
STANDBY and set the
Li
MODE
switch
to
CX.
the ON/OFF switch
to
Oh',
andthe
SlBY
sricefi
in the "operate" (out)position.
Plug
in
rbe
Xi0Z
cable connectors
and
observe the
Plate
-x
Meter.If itreads upscale,
reverse
the
mpinV0X
connector on the exciter end. The ampbfkr
phe
current must be zero with the
V05
cable
in and the exciter
m
STANDBI-.
TYPE
ACCEPTANCE
LABEL
HIGH VOLTAGE
CONNECTOR
J5
.
..
..
~,
. .. -. .
.:
-
.
-
.
.
<;,i
=
I
J6
--
.
I
;
:
CONNECTOR
I
.I
.
;
L
.
,
e;
-.
n
'
J
4
Fig.
2-1
Rear Chassis Connectors
120 VOLT OPERATION
Amplifier Power Supply
--
~~
~~
--
-
Figure
2-2.
Jumper Connectionsfor
720
Volt Operation
.+
-
-
.
...
.
~
-
..
240 VOLT OPERATION
--
-
-
.. .
.. -.
Amplifier Power Supply
-
---
-
...-
.
-
?
..*
<:
-
..-.
-.+-
.
-
Figure
2-3.
Jumper Connections for
240
Volt Operation
:;
-.
.
I.:
_
~
-
.
-
Fig.
2-4
Connecting the PS-7 Power Supply and the
R.
L. Drake Line of Compatible Exciters
OPTION
A
i
OPTION
B
INVERTEDFRONT FEET
mi
SUPPLIED WITH UNIT
SUPPLIED WITH UNIT
Fig.
2-5
Viewing Angle Options
.>
NOTES
CHAPTER
3
OPERATION
CAUTION
DONOT
turn on the L 7 Amplifier with the
cabinet removed because the high voltage
inter-lockshortsoutthe B+andwill damage
Power Supply components.
DONOT
operate
the Linear Amplifier until
it
has been
connected
to
a 50 Ohm antenna or a 50Ohm
DummyLoad.Besurethatthecorrectjumper
connections described in Chapter 2 have
--
been made in both theLinear Amplifier and
-
the Power Supply for the line voltage to be
used.
3-1. GENERAL
Figure
3-1
identifies anddescribesallfront panel
controls andindicatorsreferred
to
inthese tuning
and operating procedures. Perform the appro-
priate tuning procedures describedbelow prior
to
operation.
Forallmodesof operation,theL 7istunedupwith
a single RF frequency driving
it
and
with
the
Mode switch in CW position. The exciter may be
tuned uponCW intotheantenna
connected
to
the
amplifier by depressing the STBY switch. The
exciter shouldbe checked
to
be surethat
itis
tuned
up when driving the L 7 since the antenna wn-
nected
to
the amplser may not be exactly 50
Ohms.
..
3-2. TUNING PROCEDURE
After the exciter has been tuned up,
turn
the
exciterto standbyandrelease
theSTBYswitchon
the
L
7.
SettheMode switch(redrockerswitch)
to
CW position. The light that indicates high plate
voltage for SSB operation should be off, andthe
OPR light should be on.
The Drake TR
7
and some other exciters utilize
transmittingAGC,sometimescalledALC, during
all modes of operation.During tuneup, transmit-
ting AGC will have
to
be defeated either by un-
plugging the transmitting AGC connector,or by
turning the AGC control fully counterclockwise.
All Drake Transmitters and Transceivers except
the TR
7
and
2NT
(which has no transmitting
AGC) switch off AGC in
TUNE,
CW and
AM
modes. It is not necessary
to
defeat AGC exter-
nallyon DrakeTransmitters,otherthan
theTR-7.
3-3. CW AND RTTY TUNING
Preset the front panel controls on the L
7
as
follows:
a. Mode switch
to
CW.
b. Band switch
to
desired band.
c. Meter switch to
3000
WAm
FWD.
d. STBY switch
to
"operate" (out).
e.
LOAD
fully counterclockwise
to
zero.
f. PLATE wntrol in the arc provided for the
desiredband.
g.
Turn
AGC control fully counterclockwise.
h. ON-OFFswitch
to
ON.
Turnontheexciterandincreasetheexciteroutput
while not exceeding0.400 Amperes plate current.
Tunethe
PLATE
controlfora dipinplatecurrent.
Alternatelyadjustthe
LOAD
andPLATEcontrols
while
increasing
the exciterpower in smallincre-
ments until maximum
RF
output occurs at 0.565
plate Amperes. Because of variations in line vol-
tage
a
graph (figure
3-2)
is
supplied which corre-
lates plate voltage and plate current for 1000
WattsDC plateinputpower andshould
be
used
to
be surethatthe amplifier
is
operatingator under
the maximum legal input power.
In
case maxi-
mum legal input cannot be obtained because of
low exciter power, tunefor maximumforward
RF
Watts atmaximum exciter power.
3-4.
SSB
AND AM TUNING
Preset the front panel controls on the L7 as
follows:
a. Mode switch
to
CW.
b. Band switch
to
desired band.
c. Meter switch to IG (grid current).
d. LOAD control fully counterclockwise
to
zero.
e
.
Platewntrolinthearcprovidedforthedesired
band.
f
.
Turn AGC control fully counterclockwise.
g. STBYswitch
to
"operate" (out).
h. ON-OFFswitch
to
ON.
NOTE
Substitute
250
mA
grid currentfor200
mA
in
succeeding
test
if
'Amperex 8802/%500Z
tubes areinstalled inthe amplifier.
Turnontheexciterandincreasetheexciteroutput
while not exceeding
0.400
Amperes plate current
andtunethePLATEcontrolfora dipinplatecur-
rent. Whileincreasingtheexciterpower,maintain
-
FIGURE 3-1.FRONT PANEL CONTROLS
I.
Multimeter: Indicates plate voltage, grid current, and forward or reflected watts as selected by
meter switches
(8).
2.
Plate Current Meter: Indicates plate current.
3. Indicator Lamps:Indicate standbyor operatecondition,SSB(highpower)mode,andmultimeter
function.
4.
STBY Switch: Whendepressed, allows standby operation with the exciter connected straight
through to the antenna.
5.
AGC Control:Adjusts the transmitting AGC threshold.
6.
ON/OFFSwitch: Turns the main power on and off.
7.
MODE Switch:Selectshighplatevoltagefor SSBoperation or lowplatevoltagefor CWoperation
oifor tuning.
8.
Meter Switches: Select indication for Multimeter (1).
9.
PLATE Control:Resonates theplate tank circuit.
10.
BANDSwitch:Selects input andplate tank components toresonate theamplifierontheselected
band.
11.
LOAD Control: Adjusts the output impedance of the amplifier to match the antenna load
impedance.
-%I.
:
=-.;?
.
..+
-
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