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@Switch
the exciter to
its
"Tune"
or full CW
power
position
.
(If
an
exciter or
transceiver
with
more drive
than the
Swan
270 or
260
is used, it is recommended
that the drive be kept down to approximately 100
watts output. With the Swan 500 or 350 this is done
by inserting
approximately
250 MA
of
carrier rather
than
switching
to the
"Tune"
position). Quickly
adjust
P.A. Tune on the 1200-W for maximum out-
put,
as
indicated by the meter in "Output Metering"
position. Then go back to the exciter and adjust its
P .A. Tune for maximum output. (It may have
changed slightly when switched into the
amplifier
cathode circuit.) Next advance the P .A. Load control
on the 1200-W for increased output, and then alter-
nate between adjusting P.A. Tune and P.A. Load
until the highest possible output indication is reached.
Then,
advance
the P .A. Load control
about
I number
higher
and
adjust P.A. Tune for maximum output.
This last tuning adjustment will provide best linearity
and efficiency.
The output reading is a relative indication,
and
will
vary co,nsiderably with different antenna loads as well
as with frequency
.
The Cathode Current should read
approximately 500-600 MA. This reading is based on
100 watts of drive. With more driving power the
cathode
current will of course read higher.
CAUTION
Do not keep the exciter or transceiver in tune
position for longer than 30 seconds at a
time.
This
caution
note concerns the exciter more than the
I200- W, but since the 6LQ6 power amplifier tubes
are operating at full input during tune, the time
should
always be kept short. If longer time is
required,
switch
to standby for a minute, and then
back to tune for 30 seconds. With experience in
tuning procedures, it will be found that 30 seconds
is
more than enough time.
@
SSB Voice Operation. Having followed the preceding
tuning procedures, now
switch
the 1200-W to
"SSB-
CW" position,
and
the output metering control to
Cathode
Current. Apply SSB voice excitation from
the transceiver or driver,
and
advance its
Mic.
Gain
control
for a peak reading
of
300-400 rna
.
CAUTION:
I) Exercise
great care
in setting the Mic
Gain
control.
It is quite
easy
to produce higher meJer
readings
,
butflattopping and distortion will
result.
2)
Do not
switch
the exciter into
"Tune"
position
when
the 1200- W is in "SSB-CW" position. Only
voice
modulated
excitation should
be applied in this
position.
Q)
Monitoring
and
tuning with
an
oscillo~~cope.
A
highly
recommended piece of test equipment for the
com-
plete amateur
radio
station
is
an oscilloscope suitable
for
monitoring.
transmitter
output and
linearity. This
4
instrument
will
permit
optimum tuning of both
the
driver
and amplifier
,
as well as continuous mon-
itoring during
operation.
An excellent oscilloscope is
the Heath model
SB-6\0 sold in
kit
form
by
the
Heath Co.
of
Benton Harbor,
Michigan. The
instruc-
tion book
supplied
with this kit
explains in
detail how
to connect
and
use the instrument
,
and
how
to
interpret the
screen
patterns. Other
oscilloscopes
may
also
be used
.
The Radio
Amateur'
s
Handbook, pub-
lished by the
ARRL,
and the Radio Handbook
by
Bill Orr, published by Editors
and Engineers
both
contain detailed
information on
the use
of os-
cilloscopes
for
transmitter tuning
and operation.
These publications
are
recommended references for
this
purpose.
@To
operate
without the 1200-W,
simply switch
it to
"Bypass"
position. The
antenna
circuit is then by-
passed around the
amplifier
by the internal
relay and
the transceiver-driver will operate
"Barefoot."
How-
ever,
the 6LQ6 filaments in the 1200-W remain lit to
allow
instant operation
of
the
amplifier.
G)
CW Operation: for operation
at approximately 500
watts, the function switch may be left in the "TUNE"
position.
For
full power operation, place the
function
switch in the SSBjCW position.
MAINTENANCE
There will be little maintenance required
in
the 1200-W
amplifier
.
The
6LQ6
tubes will provide thousands
of
service
hours when operated
according
to instructions.
Deterioration of
a
tube will
generally
be indicated by
a
change in idling
current
or inability to draw normal plate
current, or both. However, except
for
occasional
field
problems which may occur
with any
electronic device,
the tubes may be
expected
to operate month
after
month
and
year
after year with no problems. In the
grounded
grid
circuit, matching of the
6LQ6
tubes is not normally
required
.
Other components are
also operating
conservatively,
and well
within
nominal ratings.
The electrolytic filter
capacitors
in the power
supply are
computer
grade,
meaning that they have
a
much higher degree
of
purity
and quality control than conventional types. Life
expec-
tancy of these filters is
approximately
\0
years
.
The
silicon
diodes used in the
supply are
hermetically
sealed
and are not likely to ever fail or wear
out.
DIAL SETTING
BAND
PLATE
LOAD
80
40
20
15
10
5
4.5
7.5
6
7
TYPICAL DIAL SETTINGS ON
1200-W WHEN COUPLED TO
A 50 OHM LOAD
3
2.5
4
3
4
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