Swann MARK II - Page 9

tion note concerns the exciter more than the
Mark II, but since the 3-500Z 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.
Dial Setting
5.5
Typical dial settings on Mark II when coupled
to a 50 ohm non-inductive load.
5. After tuning all controls for maximum output
indication as described, other meter readings
may be observed. IG (grid current) should indi-
cate .2 to.3 amperes in TUNE position, depend-
ing on the amount of driving power. Swan
transceivers will generally supply more driving
power than others presently on the market. How-
ever, most transceivers will provide enough to
drive the Mark II to full legal power. IP (plate
current) should indicate at least .6 amps, and
up to .9 amps, depending-on driving power.
The exact values of grid &nd plate current are
not critical providing they do not exceed .6 grid
amperes, and .9 plate amperes, and this only
during short tuning periods.
. SSB Voice Operation. Having followed the pre-
ceeding tuning procedures, now switch the Mark
II to"SSB" position, and its meter switch to "IP."
Apply SSB voice exitation from the transceiver
or driver, and advance its Mic. Gain control for
an average IP reading of .40 amperes. Only
occasional voice peaks should kick up to .6
amps.
CAUTION (1). Exercise great care in setting
the Mic. Gain control. It is quite easy to
produce higher meter readings, but flat-
topping and distortion will result, as well
as the possibility of exceeding legal power
limits.
CAUTION (2). Do not switch the exciter
into "TUNE" position when the Mark II
is in "SSB" position. Only voice modu-
lated excitation should be applied in this
position.
. Monitoring and tuning with an oscilloscope. A
highly recommended piece of test equipment for
the complete amateur radio station is an oscil-
loscope suitable for monitoring transmitter out-
put and linearity. This instrument will permit
optimum tuning of both the driver and amplifier,
as well as continuous monitoring during opera-
tion.
10.
Hy
An excellent oscilloscope for this purpose
is the Heath model SB-610 sold in kit form by
the Heath Company of Benton Harbor, Michi-
gan. The instruction book supplied with this kit
explains in detail how to connect and use the
instrument, and how to interpret the screen pat-
terns. Other oscilloscopes may also be used.
The Radio Amateur's Handbook, published 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.
. When the Mark II Function Switch is in"SSB"
position for voice transmission, plate voltage is
increased
from
the
TUNE-CW
value.
In
Stand-
by
or
Receive
condition,
the
3-500Z
tubes
are
biased
to
cut-off,
so
IP
will
be
zero,
and
EP
will
indicate
2900
to
3000
volts,
depending
on
power
line
voltage.
In
TRANSMIT
position,
without
moduiativn,
IP
will
show
an
idling
current
of
.28
amperes,
and
EP
will
drop
to
2650
volts.
With
voice
modulation
averaging
.40
amperes,
EP
will
drop
to
about
2500
volts.
Occasional
voice
syllables
may
drop
the
plate
voltage
fur-
ther,
but
with
proper
setting
of
the
Mic.
Gain
control,
dynamic
regulation
of
the
power
supply
is
more
than
adequate.
Use
of
computer
grade
electrolytics
assures
long
capacitor
life,
with
a
filter
capacity
of
40
mfd.
across
the
plate
supply.
(All
voltage
readings
above
are
subject
to
line
voltage variations).
. To operate without the Mark II Linear Ampli-
fier, simply switch it to "Power OFF" position.
The antenna circuit is then by-passed around the
amplifier by the internal relay and the trans-
ceiver-driver will operate "Barefoot". When
switching back to amplifier use, allow a few sec-
onds for filament warm up.
CW Operation. To operate CW with the Mark
II always keep the Function Switch in the TUNE-
CW position in order to limit input power to
1000 watiz. CAUTION: Because the Mark II
uses a grounded grid amplifier circuit, input
power measurements must include the driver
stage input. If for example, the driver is run-
ning 300 watts input, the linear amplifier input
must be limited to 700 watts when in CW Mode.
Thus, ycu must first measure driver input, in
order to determine how much input you may
run to the Mark II. Use the EP meter position
to measure plate voltage, and then calculate how
much IP (plate current) you can run and stay
within the legal limit. Then use the P.A. Load
control to hold IP down to this level.
AM
Operation.
The
Mark
II
Linear
Amplifier
may
be
operated
in
the
"AM"
mode
at
1000
watts
D.C.
input
and
100
percent
modulation.
When
using
a
transceiver
or
exciter
which
will
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