CPI 4CX250B-M

The Eimac 4CX250B/M is a ceramic/metal,
forced-air cooled external-anode tetrode with a
maximum anode dissipation rating of 250 Watts.
The 4CX250B/M is intended for use in applications where tight control of electrical specifications is required and replaces the 4CX250B in
all applications. This tube utilizes a ruggedized
internal structure and utilizes a welded anode cap
for improved reliability.
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ELECTRICAL
Cathode: Oxide coated, Unipotential
Filament Voltage
Current at 6.0 Volts
6.0± 0.3 V
2.6 A
Direct Interelectrode Capacitances (grounded cathode) 2
Cin
15.7 pF
Cout
4.5 pF
Cgp
0.04 pF
Amplification Factor, Average (screen-grid)
5
Frequency of Maximum Ratings (CW)
500 MHz
MECHANICAL:
Overall Dimensions:
Length
2.46 in; 62.5 mm
Diameter
1.64 in; 41.7 mm
Weight (approx.)
4 oz; 113 gm
Operating Postition
Any
Maximum Operating Temperature:
Ceramic/Metal Seals & Envelope
250° C
Anode Core
250° C
Cooling
Forced Air
Base
Special, 9-pin Jedec-B8-236
Recommended Air System Socket
SK-600 Series
Recommended Air Chimney
SK-606
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BEAM POWER TETRODE 4CX250B/M / 7203A
CPI | RADIAL
4CW50,000J
RADIAL BEAM POWER TETRODE
4CX250B/M
7203A
Characteristics
Characteristics and operating values are based upon performance tests. These figures may change without notice as the result of additional data or product refinement.
CPI MPP, Eimac Operation should be consulted before using this information for final equipment design.
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Capacitance values are for a cold tube as measured in a special shielded fixture in accordance with Electronic Industries Association Standard RS-191.
RANGE VALUES FOR EQUIPMENT DESIGN
Min.
Nom.
Max.
Filament Current @ 6.0 Volts
Cathode Warm-up Time
2.3
30
--
60
2.9
--
Interelectrode Capacitance 1 (grounded cathode circuit)
Cin
Cout
Cgp
14.2
4.0
--
--
--
--
17.2
5.0
0.06
pF
pF
pF
Interelectrode Capacitance 1 (grounded grid circuit)
Cin
Cout
Cpk
--
4.0
--
13.0
--
0.01
--
5.0
--
pF
pF
pF
1
Amperes
Seconds
Capacitance values are for a cold tube as measured in a shielded fixture in accordance with Electronic Industries Assocation Standard RS-191.
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
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CPI | RADIAL BEAM POWER TETRODE 4CX250B/M / 7203A
RADIAL BEAM POWER TETRODE
4CX250B/M
7203A
TYPICAL OPERATION
Measured Values, Grid-Driven
RADIO FREQUENCY AMPLIFIER
Class C, CW Operation
ANODE VOLTAGE
500 1000
1500 2000 Vdc
SCREEN VOLTAGE
250
250
250
250 Vdc
GRID VOLTAGE
-90
-90
-90
-90 Vdc
ANODE CURRENT
250
250
250
250 mAdc
SCREEN CURRENT
45
38
21
19 mAdc
1
GRID CURRENT 35 31
28 26mAdc
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DRIVING POWER 4.0 3.5 3.2 2.9Watts
3,4
USEFUL OUTPUT 70
190
280 390 Watts
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Approximate Values
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­ Approximate, measured in VHF service
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Approximate, delivered to the load
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For measured case; may vary from tube to tube
ABSOLUTE MAXIMUM RATINGS:
ANODE VOLTAGE
SCREEN VOLTAGE
ANODE CURRENT
PLATE DISSIPATION
SCREEN DISSIPATION
GRID DISSIPATION
HEATER-TO-GRID VOLTAGE
2000 300
0.250
250
12 2
150
Vdc
Vdc
Adc
Watts
Watts
Watts
Volts
NOTE: TYPICAL OPERATION data are obtained from direct measurement or by calculation from published characteristic curves. Adjustment
of the rf grid voltage (feedback) to obtain the specified anode current at the specified bias and anode voltages is assumed. If this procedure is
followed, there will be little variation in output power when the tube is changed.
application
mechanical
MOUNTING - The 4CX250B/M may be mounted in any position.
SOCKETING - The Eimac SK-600 series air system sockets or a
socket having equivalent characteristics is required. Sockets are
available with or without built-in screen capacitors and may be
obtained with either grounded or ungrounded cathode terminals.
COOLING – Sufficient forced-air cooling must be provided for
the anode, base seals, and body seals to maintain operating temperatures below the rated maximum values. Air requirements to
maintain anode core temperatures at 200°C with an inlet air temperature of 50°C are tabulated below. These requirements apply
when a socket of the Eimac SK-600 series and an Eimac SK-606
chimney are used with an air flow in the base-to-anode direction.
Tube life is prolonged if the anode temperature is maintained at
values lower than the maximum rating.
The blower selected in a given application must be capable of
supplying the desired airflow at a back pressure equal to the
pressure drop shown in the chart plus any drop encountered in
ducts and filters. The blower must be designed to deliver necessary airflow at the desired altitude.
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SEA LEVEL
Anode
Dissipation
(Watts)
200
250
Air Flow Pressure
(CFM)
Drop
(In. of Water)
5.0
6.4
0.52
0.82
10,000 FEET
Air Flow
(CFM)
7.3
9.3
Pressure
Drop
(In. of Water)
0.76
1.20
At 500 MHz or below base cooling air requirements are satisfied
automatically when the tube is used in an EIMAC Air-System
socket and the recommended air flow rates are used. Experience
has shown that if reliable long life operation is to be obtained, the
cooling air flow must be maintained during standby periods when
only the heater voltage is applied to the tube. The anode cooler
should be inspected periodically and cleaned when necessary to
remove any dirt which might interfere with effective cooling.
VIBRATION – The 4CX250B/M is capable of withstanding shock
and vibration, such as encountered in shipment and normal handling. The tubes will function well in environments where shock
and vibration are anticipated.
HEATER OPERATION - The rated heater voltage for the
4CX250B/M, 6.0 volts as measured at the socket, should be
maintained at this value to obtain optimum performance and
maximum tube life. In no case should the voltage be allowed to
deviate from 6.0 volts by more than plus or minus five percent
(5%). Short-time changes of +/- 10% will not damage the tube,
but variations in performance must be expected. The heater
voltage must be maintained within +/- 5% to minimize these
variations and to obtain maximum tube life.
At frequencies above approx. 300 MHz transit-time effects begin to influence the cathode temperature. The amount of driving
power diverted to heating the cathode by back-bombardment
will depend upon frequency, anode current, and driving power.
When the tube is driven to maximum input as a class-C amplifier, the heater voltage should be reduced according to the table
below:
Frequency MHz
300 and lower
301 to 400
401 to 500 Heater Voltage
6.00 Volts
5.76 Volts
5.50 Volts
CATHODE OPERATION - The oxide coated unipotential cathode
must be protected against excessively high emission currents.
The maximum rated dc input current is 200 mA for plate modulated operation and 250 mA for all other types of operation with
the exception of pulsed applications.
The cathode is connected internally to four pins and all four
should be used to make connection to external circuits to lower inductance. At radio frequencies it is important to keep the
cathode leads short and direct and to use conductors with large
areas to minimize the inductive reactances in series with the
cathode leads.
It is recommended that the rated nominal heater voltage be applied for a minimum of 30 seconds before other operating voltages are applied. Where the circuit design requires the cathode
and heater to be operated at different potentials, the rated
maximum heater-to-cathode voltage of 150 voltage should be
observed, regardless of polarity.
GRID OPERATION - The maximum rated dc grid bias voltage is
-250 volts and the maximum grid dissipation rating is 2.0 Watts.
In ordinary audio and rf amplifiers the grid dissipation usually
will not approach the maximum rating. At operating frequencies above the 100 MHz region, driving power requirements for
amplifiers increase noticeably. At 500 MHz as much as 20 Watts
of driving power may have to be supplied. However, most of the
driving power is absorbed in circuit losses other than grid dissipation, so that grid dissipation is only increased slightly. Satisfactory 500 MHz operation of the tube in a stable amplifier is
indicated by grid-current values below approx. 15 mA. The
maximum permissible grid-circuit resistance per tube is 100K
Ohms.
SCREEN OPERATION - The maximum rated dissipation for
the screen grid is 12 Watts and the screen input power must
be kept below that level. The product of peak screen current
and peak screen voltage approximates the screen input power
when amplitude modulation is used. In some cases screen current may tend to be negative. The 4CX250B/M shows reduced
screen current, compared to the 4CX250B, and is therefore
preferred for use in amplifiers where screen supply voltage
regulation is poor or where an increase in screen current above
the normal value will cause a significant reduction in voltage.
At UHF increased output (cavity) loading is recommended to
reduce screen current even if the overall tube efficiency is reduced somewhat.
FAULT PROTECTION - All power tubes operate at voltages
which can cause severe damage in the event of an internal arc,
especially in those cases where large amounts of stored energy or follow-on current are involved. Some means of protection is advised in all cases, and it is recommended that a series
resistor be used in the anode circuit (20 to 50 ohms) to limit
peak current and provide a means of dissipating the energy in
the event of a tube or circuit arc. For an oxide-cathode tube
such as the 4CX250B/M a maximum of 4 joules total energy
may be permitted to be dumped into an internal arc. Amounts
in excess of this may permanently damage the cathode or the
tube grids. Additional information is found Eimac’s Application
Bulletin #17 titled “FAULT PROTECTION,” available on request.
RADIAL BEAM POWER TETRODE 4CX250B/M / 7203A
ELECTRICAL
CPI |
RADIAL BEAM POWER TETRODE
4CX250B/M
7203A
RF 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 affect. Public health agencies are concerned with hazard even at these frequencies. OSHA (Occupational Safety and Health Administration) recommends that
prolonged exposure to rf radiation should be limited to 10 milliwatts per square centimeter.
INTERELECTRODE CAPACITANCE - The actual internal interelectrode 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 tube, as the key component
involved, the industry and the 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
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RADIAL BEAM POWER TETRODE 4CX250B/M / 7203A
CPI |
RADIAL BEAM POWER TETRODE
4CX250B/M
7203A
period of time, even when the tube may be made by different
manu-facturers. 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.
HOT SURFACES - Air-cooled surfaces and other parts of tubes
can reach temperatures of several hundred degrees C and
cause serious burns if touched for several minutes after all
power is removed.
HIGH VOLTAGE - The 4CX250B/M operates at voltages which
can be deadly, and the equipment must be designed properly
and operating precautions must be followed. Equipment must
be designed so that no one can come in contact with high voltages. All equipment must include safety enclosures for highvoltage circuits and terminals, with interlock switches to open
the primary circuits of the power supplies and to discharge
high-voltage condensers 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.
SPECIAL APPLICATIONS - If it is desired to operate this tube
under conditions widely different from those given here, contact
the Application Engineering Dept., CPI MPP Eimac Operation,
Palo Alto, Calif. 94304 for information and recommendations.
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 the 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.
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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).
Please review the detailed Operating Hazards sheet enclosed
with each tube, or request a copy from CPI MPP, Eimac Operation Application Engineering at 1-650-592-1221.
CPI | 4CW50,000J
RADIAL BEAM POWER TETRODE 4CX250B/M / 7203A
RADIAL BEAM POWER TETRODE
4CX250B/M
7203A
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CPI |
RADIAL BEAM POWER TETRODE 4CX250B/M / 7203A
RADIAL BEAM POWER TETRODE
4CX250B/M
7203A
CPI | RADIAL BEAM POWER TETRODE 4CX250B/M / 7203A
RADIAL BEAM POWER TETRODE
4CX250B/M
7203A
CPI 072011
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