Heathkit DX-40 - SERVICE AND MAINTENANCE HINTS; Stage-Specific Fault Diagnosis; Operational Issues and Antenna Concerns

Switching the operation switch to either the PHONE or CW position will provide the full line volt-
age at socket connections #5 and #6. CAUTION: This switch breaks only one side of the line,
consequently socket connection #5 is always "alive" withthe linevoltage. Weurge that due safety
precautions be observed when connections are made to the accessory socket and relay circuit.
SERVICE AND MAINTENANCE HINTS
WARNING:
Voltages
dangerous
to
life
are
present
at
practically
all
points
on
the
chassis.
The
Heath
Company
will
not
be
responsible
for
injuries
which
could
occur
while
making
tests.
Do
not
attempt
to
make
voltage
checks
or
service
the
transmitter
without
taking
standard
precautions
and
using
the
proper
equipment.
If
in
doubt,
secure
the
assistance
of
a
competent
technician.
IMPORTANT:
Read
list
of
errors
that
could
possibly
damage
your
transmitter.
General Service
Analyzing and Isolating Difficulties
Power Supply
Oscillator Stage
Buffer Stage
Final Amplifier Stage
Speech Amplifier and Modulator Stages
Grid Drive -- See Oscillator and Buffer Sections
Plate
Current
--
See
Final
Amplifier
Section
and
Antenna
Considerations.
Meter Circuit
Antenna Considerations and TVI.
Listed below are several of the common mistakes that can permanently damage components in
your transmitter. Oftentimes while hunting for a minor difficulty in a particular section of the
transmitter with the power on, components in another section may be seriously damaged. For
example, a high current will be flowing in the final amplifier tube if the fina] tuning contro} is
not in resonance while observing grid drive readings with the operation switch in the CW posi-
tion. Switch to the TUNE position.
1. Don't make voltage checks without proper safety precautions. Voltage checks should be done
without any distraction. Children shouldnot be allowednear the equipment. Electric shock
can be fatal.
2. Don't turn the transmitter to the CW or PHONE position unless you have first obtained a
reasonable grid drive reading on the TUNE position.
3.
Don't
operate
the
transmitter
without
proper
crystals
installed,
or
the
VFO
tuned
to
the
proper
frequency.
Be
sure
the
CRYSTAL-VFO
switch
is
turned
to
the
proper
position.
4. Don't leave the transmitter in operation over 5 minutes, even when testing. The duty cycle
of the power transformer is 5 minutes on and 10 minutes off. This, of course, refers to
continuous operation and does not apply to CW or PHONE operation. PHONE or CW opera-
tion under normal operating conditions will not approach the maximum limit.
5. Don't cover the ventilation holes provided in the cabinet.
6. Don't test the oscillator, buffer or modulator stages with the final amplifier on PHONE or
CW position if it is not dipped to resonance as indicated by minimum plate current.
Don't try to read grid current to the final amplifier:
When the key circuit is open.
When the meter switch is in the plate position.
With
an
improper
crystal
(the
drive
control
tunes
a
limited
range).
With
the
CRYSTAL-VFO
switch
in
the
wrong
position.
poop
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