CPI 4CX25

Characteristics1
The EIMAC 4CX25,000C is a ceramic/metal power
tetrode intended for use as a VHF power amplifier.
It features a type of internal mechanical structure
which results in high rf operating efficiency. Low
rf losses in this structure permit operation at full
ratings to 110 MHz.
ELECTRICAL
Filament: Thoriated Tungsten Mesh
Voltage
10.0± 0.5 V
Current at 10.0 Volts
140 A
Amplification Factor, Average, Grid to Screen 6.7
Direct Interelectrode Capacitances (grounded cathode)2
Cin
195 pF
Cout
22.7 pF
Cgp
0.6 pF
Direct Interelectrode Capacitances (grounded grid and screen) 2
Cin
87.4 pF
Cout
23.1 pF
0.08 pF
CPK
Maximum Frequency for Full Ratings (CW)
110 MHz
MECHANICAL:
Maximum Overall Dimensions:
Length
10.1 in; 256.54 mm
Diameter
8.9 in; 226.0 mm
Net Weight
26.5 lbs. 58.3 kg
Operating Position
Vertical, Base Up or Down
Maximum Operating Temperature:
Ceramic/Metal Seals
250° C
Anode Core
250° C
Cooling
Forced Air
Base
Special, Coaxial
Recommended Socket for VHF
Eimac SK-360
Recommended Socket for dc to HF
Eimac SK-320
The 4CX25,000C is recommended for use in InBand-on-Channel (IBOC) FM broadcast service
with combined digital and analog components.
The anode is rated for 25 kilowatts of dissipation
with forced-air cooling and incorporates a compact, highly efficient cooler of new design.
1
Characteristics and operating values are based upon performance tests.
2
BEAM POWER TETRODE 4CX25,000C
CPI | RADIAL
4CW50,000J
RADIAL BEAM POWER
TETRODE 4CX25,000C
In shielded fixture.
Maximum RatingsTypical Operation
The values listed above represent specified limits for the product and are subject to change. The data should be used for basic
information only. Formal, controlled specifications may be obtained from CPI for use in equipment design.
For information on this and other CPI products, visit our website at: www.cpii.com,
or contact: CPI MPP, Eimac Operation, 607 Hansen Way, Palo Alto, CA 94303
telephone: 1(800) 414-8823. fax : (650) 592-9988 | email : powergrid@cpii.com
July 2011
1
CPI | RADIAL BEAM POWER TETRODE 4CX25,000C
4CX25,000C
RADIO FREQUENCY POWER AMPLIFIER
CATHODE GROUNDED
FM continuous service
Grid Driven Class C
ABSOLUTE MAXIMUM RATINGS:
DC ANODE VOLTAGE
DC SCREEN VOLTAGE
DC GRID VOLTAGE
DC ANODE CURRENT
ANODE DISSIPATION
SCREEN DISSIPATION
GRID DISSIPATION
13.0 2.0 -1.5
5.0 20 450 200 kilovolts
kilovolts
kilovolts
Amperes
kilowatts
Watts
Watts
RADIO FREQUENCY POWER AMPLIFIER
GRIDS GROUNDED FOR RF
FM continuous service
Cathode driven Class B
ABSOLUTE MAXIMUM RATINGS:
DC ANODE VOLTAGE
DC SCREEN VOLTAGE
DC GRID VOLTAGE
DC ANODE CURRENT
ANODE DISSIPATION
SCREEN DISSIPATION
GRID DISSIPATION
13.0 kilovolts
2.0 kilovolts
-1.5 kilovolts
5.0 Amperes
20 kilowatts
450 Watts
200 Watts
TYPICAL OPERATION (Measured data at 107.1 MHz):
ANODE VOLTAGE
9.0 11.5 12.0 kVdc
SCREEN VOLTAGE
800 650 1000 Vdc
GRID VOLTAGE
-300 -400 -500 Vdc
ANODE CURRENT
4.15 3.75 3.54 Adc
SCREEN CURRENT*
200
160
238 mAdc
GRID CURRENT*
38
60
53 mAdc
DRIVING POWER*
360 405
340 W
Useful Power Output*#
28.9 33.2 34.4 kW
EFFICIENCY*
77.477.681.0 %
POWER GAIN*
19.0 19.1 20.0 dB
* Will vary from tube to tube
# Delivered to load (1:1.1 VSWR)
TYPICAL OPERATION (Measured data at 97.6 MHz):
ANODE VOLTAGE
SCREEN VOLTAGE
GRID BIAS VOLTAGE
ANODE CURRENT
SCREEN CURRENT*
GRID CURRENT*
DRIVING POWER*
USEFUL POWER OUTPUT#
POWER GAIN
* Will vary from tube to tube
# Delivered to load (1:1.1 VSWR)
11.0
900
-200
4.1
235
30
1025
36.1
15.5
kVdc
Vdc
Vdc
Adc
mAdc
mAdc
W
kW
dB
NOTE: TYPICAL OPERATION data are obtained by actual measurement or by calculation from published characteristic curves. To obtain
the anode current shown at the specified bias, screen and anode voltages, adjustment of rf grid voltage is assumed. If this procedure is
followed, there will be little variation in output power when the tube is replaced, even though there may be some variation in grid and
screen currents. The grid and screen currents which occur when the desired anode current is obtained are incidental and vary from tube to
tube. These current variations cause no performance degradation providing the circuit maintains the correct voltage in the presence of the
current variations.
RANGE VALUES FOR EQUIPMENT DESIGN
Filament Current at 10.0 volts
2
Min
135
Nom Max
--- 146
A
MECHANICAL
STORAGE - If a tube is to be stored as a spare it should
be kept in its original shipping carton, with the original
packing material, to minimize the possibility of handling
damage.
MOUNTING - The 4CX25,000C must be operated with
its axis vertical. The base of the tube may be up or down
at the convenience of the designer.
SOCKET - The EIMAC Air-System Socket type SK-320
is designed for use with the 4CX25,000C in dc or LF/
HF applications. For VHF applications a type SK-360
air-system socket is recommended. The use of the
recommended air flow through an air-system socket will
provide effective cooling of the base.
COOLING - The maximum temperature rating for the
external surfaces of this tube is 250°C, and sufficient
forced-air cooling must be used in all applications to
keep the temperature of the anode (at the base of the
cooling fins) and the temperature of the ceramic/metal
seals comfortably below this rated maximum.
It is considered good engineering practice to design for
a maximum anode core temperature of 225°C. Temperature-sensitive paints are available for checking base
and seal temperatures before any design is finalized. CPI
EIMAC Application Bulletin #20 titled “Measuring Temperature of Power Grid Tubes” is available on request.
It is also good practice to allow for variables such as
dirty air filters, rf seal heating, and the fact that the
anode cooling fins may not be clean if the tube has been
in service for a considerable length of time. Special
attention is required in cooling the center of the stem
(base), by means of special directors or some other
provision.
An air interlock system should be incorporated in the
design to automatically remove all voltages from the
tube in case of even partial failure of the tube cooling air.
Sensing exhaust air temperature is recommended.
Minimum air flow requirements for a maximum anode
temperature of 225°C (or a maximum outlet air temperature of 160°C, whichever is reached first) for various
altitudes and dissipation levels are listed on page 4.
Pressure drop values are approximate and are for the
tube anode cooler only. Pressure drop in a typical installation will be higher because of system loss and back
pressure in ducting.
CPI | RADIAL BEAM POWER TETRODE 4CX20,000C
4CX25,000C
When long life and consistent performance are factors
cooling in excess of minimum requirements is normally
beneficial.
If all cooling air is not passed around the base of the
tube and through the socket, then arrangements must be
made to assure adequate cooling of the tube base and
the socket contacts. Movement of cooling air around
the base of the tube accomplishes a double purpose in
keeping the tube base and the socket contact fingers at
a safe operating temperature.
The contact fingers in the socket are made of beryllium
copper. If this material is allowed to reach 150°C and
held there for an appreciable length of time the fingers
may lose their temper, or springy characteristics. If this
were to happen poor contact and resultant arcing can
take place which can burn/melt the metal at the tube
surface, which is a part of the vacuum envelope. Catastrophic tube loss could occur.
Air flow must be applied before or simultaneously with
the application of power, including the tube filament and
should normally be maintained for a short period of time
after all power is removed to allow for tube cool down.
Pressure drop will be higher if the SK-360 socket is used
unless additional air passages are provided around the
mounted socket.
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CPI | RADIAL BEAM POWER TETRODE 4CX25,000C
4CX25,000C
Inlet Air Temperature = 25°C
Anode
Air Flow Pressure
Dissipation
(CFM) Drop
(kilowatts)
(In. of Water)
Sea Level
12.5 257
0.6
15.0 367
1.0
17.5 498
1.5
20.0 652
2.4
5000 Feet
12.5 311
0.6
15.0 444
1.1
17.5 603
1.7
20.0 789
2.7
10,000 Feet
12.5 377
0.7
15.0 537
1.2
17.5 730
1.9
20.0 955
3.0
Inlet Air Temperature = 50°C
Anode
Air Flow
Pressure
Dissipation
(CFM)
Drop
(kilowatts)
(In. of Water)
Sea Level
12.5
379
0.9
15.0
540
1.6
17.5
733
2.6
20.0
960
4.1
5000 Feet
12.5
459
1.0
15.0
654
1.8
17.5
888
3.0
20.0
1162
4.7
10,000 Feet 12.5
555
1.1
15.0
791
2.0
17.5
1075
3.4
20.0
1407
5.4
ELECTRICAL
ABSOLUTE MAXIMUM RATINGS - Values shown for
each type of service are based on the “absolute system”
and are not to be exceeded under any service conditions.
Ratings are limiting values outside which the serviceability
of the tube may be impaired.
Inlet Air Temperature = 35°C
Anode
Air Flow
Pressure
Dissipation (CFM)
Drop
(kilowatts)
(In. of Water)
Sea Level
12.5
299
0.7
15.0
426
1.2
17.5
579
1.9
20.0
758
2.9
5000 Feet
12.5
362
0.7
15.0
516
1.3
17.5
701
2.1
20.0
917
3.3
10,000 Feet
12.5
438
0.8
15.0
625
1.4
17.5
848
2.4
20.0
1111
3.8
4
In order not to exceed absolute ratings the equipment designer has the responsibility of determining an average design value for each rating below the absolute value of that
rating by a safety factor so that the absolute values will
never be exceeded under any usual conditions of supplyvoltage variation, load variation, or manufacturing variation
in the equipment itself. It does not necessarily follow that
combinations of absolute maximum ratings can be attained
simultaneously.
FILAMENT WARMUP - In-rush current should be limited
to 300 amperes. A suitable step-start procedure can accomplish this, or an impedance-limited transformer designed for this purpose can be used. Once normal filament
voltage has been applied, a warm-up period of five seconds
is generally sufficient before commencing operation at full
power.
FILAMENT OPERATION - This tube is designed for commercial service, with no more than one normal off/on filament cycle per day. If additional cycling is anticipated it is
recommended the user contact an Applications Engineer at
CPI Eimac for additional information.
With a new tube, or one that has been in storage for some
period of time, operation with filament voltage only applied
for a period of 30 to 60 minutes is recommended before full
operation begins. This allows the active getter mounted
within the filament structure to absorb any residual gas
molecules, which have accumulated during storage.
At rated (nominal) filament voltage the peak emission capability of the tube is many times that needed for communications service. A reduction in filament voltage will lower the
filament temperature, which will substantially increase life
expectancy. The correct value of filament voltage should
be determined for the particular application. It is recommended the tube be operated at full nominal voltage for an
initial stabilization period of 100 to 200 hours before any
action is taken to operate at reduced voltage. The voltage
should gradually be reduced until there is a slight degradation in performance (such as power output or distortion.)
The voltage should then be increased a few tenths of a
volt above the value where performance degradation was
noted for operation. The operating point should be rechecked after 24 hours.
Filament voltage should be closely regulated when voltage
is to be reduced below nominal in this manner, to avoid any
possible adverse influence by normal line voltage variations.
Periodically throughout the life of the tube the procedure
outlined above for voltage reduction should be repeated
with voltage reset as required, to assure best tube life.
Filament voltage should be measured at the tube base or
socket with a known-accurate rms-responding meter.
EIMAC Application Bulletin #18 titled “Extending Transmitter Tube Life” contains valuable information and is available on request.
ELECTRODE DISSIPATION RATINGS - The maximum
dissipation ratings for the 4CX25,000C must be respected
to avoid damage to the tube. An exception is the anode
dissipation which may be permitted to rise above the rated
maximum during brief periods (ten seconds maximum) such
as may occur during tuning.
GRID OPERATION - The maximum rated control grid dissipation is 200 Watts, determined approximately by the
product of the dc grid current and the peak positive grid
voltage. A protective spark-gap device should be connected between the control grid and the cathode to guard
against excessive voltage. The maximum dc grid voltage
(bias) is -1.5 kvdc.
SCREEN OPERATION - The maximum screen grid dissipation is 450 Watts. With no ac applied to the screen grid,
dissipation is simply the product of dc screen voltage and
the dc screen current. With modulation dissipation is dependent on rms screen voltage and rms screen current.
CW operation at VHF frequencies above the maximum
frequency rating for CW service may add significantly to
the total screen grid dissipation due to the ac charging
current in internal capacitance between the screen grid
and anode. Operation at lower anode voltage and/or lower
drive levels will reduce the dissipation.
Anode voltage, anode loading, or bias voltage must never
be removed while filament and screen voltages are present, since screen dissipation ratings will be exceeded. A
protective spark-gap device should be connected between
the screen grid and the cathode to guard against excessive
voltage.
BEAM POWER TETRODE 4CX25,000C
CPI | RADIAL
4CW50,000J
4CX25,000C
The tube may exhibit reversed (negative) screen current
under some operating conditions. The screen supply voltage must be maintained constant for any values of negative
and positive screen current which may be encountered.
Dangerously high anode current may flow if the screen
power supply exhibits a rising voltage characteristic with
negative screen current. Stabilization may be accomplished with a bleeder resistor connected from screen to
cathode to assure that net screen supply current is always
positive. This is essential if a series electronic regulator is
employed.
FAULT PROTECTION - In addition to the normal anode
over-current interlock, screen current interlock, and cooling air flow interlock, the tube must be protected from internal damage caused by an internal anode arc which may
occur at high voltages. A protective resistance of approx. 5
to 10 Ohms, 500 Watts should always be connected in series with the tube anode to absorb power supply stored energy if an internal arc should occur. If power supply stored
energy is high an electronic crowbar, which will discharge
power supply capacitors in a few microseconds after the
start of an arc, is recommended. The protection criteria for
each electrode supply is to short each electrode to ground,
one at a time, through a vacuum relay switch and a 6-inch
section of #30 AWG copper wire. The wire will remain intact if protection is adequate. EIMAC’s Application Bulletin
#17 titled “Fault Protection” contains considerable detail
and is available on request.
HIGH VOLTAGE - Normal operating voltages used with this
tube are deadly. The equipment must be designed properly
and operating precautions must be followed. Design all
equipment so that no one can come in contact with high
voltages. All equipment must include safety enclosures for
5
CPI | RADIAL BEAM POWER TETRODE 4CX25,000C
4CX25,000C
high voltage circuits and terminals, with interlock switches to open primary circuits of the power supply and to
discharge high voltage capacitors whenever access doors
are opened. Interlock switches must not be bypassed or
“cheated” to allow operation with access doors open.
Always remember that HIGH VOLTAGE CAN KILL.
RADIO-FREQUENCY RADIATION - Avoid exposure to
strong rf fields even at relatively low frequency. Absorption of rf energy by human tissue is dependent on
frequency. Under 300 MHz most of the energy will pass
completely through the human body with little attenuation
or heating effect. Public health agencies are concerned
with the hazard, and the published OSHA (Occupational
Safety and Health Administration) or other local recommendations to limit prolonged exposure of rf radiation
should be followed.
INTERELECTRODE CAPACITANCE - The actual internal
electrode capacitance of a tube is influenced by many
variables in most applications, such as stray capacitance
to the chassis, capacitance added by the socket used,
stray capacitance between tube terminals and wiring
effects. To control the actual capacitance values within
the tubes, as the key component involved, the industry
and Military Services use a standard test procedure as
described in Electronic Industries Association Standard
RS-191. This requires the use of specially constructed test
fixtures which effectively shield all external tube leads
from each other and eliminates any capacitance reading to
“ground.” The test is performed on a cold tube. Other factors being equal, controlling internal tube capacitance in
this way normally assures good interchangeability of tubes
over a period of time, even when the tube may be made by
different manufacturers.
The capacitance values shown in the manufacturer’s
technical data, or test specifications, normally are taken in
accordance with Standard RS-191.
The equipment designer is therefore cautioned to make allowance for the actual capacitance values which will exist
in any normal application. Measurements should be taken
with the socket and mounting which represent approximate final layout if capacitance values are highly significant in the design.
SPECIAL APPLICATIONS - When it is desired to operate this tube under conditions widely different from those
listed here, write to CPI MPP, Eimac Operation, Applications Engineering, 607 Hansen Way, Palo Alto, CA 94304
U.S.A.
OPERATING HAZARDS
Proper use and safe operating practices with respect to power tubes are the responsibility of equipment manufacturers and users
of such tubes. All persons who work with and are exposed to power tubes, or equipment that utilizes such tubes, must take precautions to protect themselves against possible serious bodily injury. DO NOT BE CARELESS AROUND SUCH PRODUCTS.
The operation of this tube may involve the following hazards, any one of which, in the absence of safe operating practices and precautions, could result in serious harm to personnel.
HIGH VOLTAGE – Normal operating voltages can be deadly.
Remember that HIGH VOLTAGE CAN KILL.
LOW-VOLTAGE HIGH-CURRENT CIRCUITS - Personal jewelry,
such as rings, should not be worn when working with filament
contacts or connectors as a short circuit can produce very high
current and melting, resulting in severe burns.
RF RADIATION – Exposure to strong rf fields should be avoided,
even at relatively low frequencies. CARDIAC PACEMAKERS
MAY BE AFFECTED.
6
HOT SURFACES – Surfaces of tubes can reach temperatures
of several hundred°C and cause serious burns if touched for
several minutes after all power is removed.
MATERIAL COMPLIANCE - This product and package conforms
to the conditions and limitations specified in 49CFR 173.424 for
radioactive material, excepted package-instruments or articles,
UN2910. In addition, this product and package contains no
beryllium oxide (BeO).
CPI | RADIAL BEAM POWER TETRODE 4CX25,000C
4CX25,000C
7
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CPI | RADIAL BEAM POWER TETRODE 4CX25,000C
4CX25,000C