CPI 4CM2500KG_11

The EIMAC 4CM2500KG is a ceramic/metal, multiphase (water/vapor) cooled power tetrode designed for very high power rf service.
The 4CM2500KG has a high density thoriated
tungsten mesh filament mounted on water-cooled
supports. Pyrolytic graphite control and screen
grids are used to provide stability at high dissipation. The maximum anode dissipation rating is
2500 kilowatts.
Large diameter coaxial control grid and cathode
terminals allow enhanced VHF performance. Filament power and filament support cooling water are
supplied through connectors which allow for quick
tube installation and replacement.
Filament: Thoriated Tungsten Mesh
15.5 V
Current at 15.5 Volts (nominal)
640 A
Frequency of Maximu Ratings (CW)
130 MHz
Maximum Useful Frequency
Over 200 MHz
Amplification Factor, Average, Grid to Screen 6
Direct Interelectrode Capacitances (grounded cathode):
1110 pF
150 pF
5.5 pF
Direct Interelectrode Capacitances (grounded grid and screen) 2
385 pF
152 pF
0.07 pF
cooled power tetrode 4cm2500kg
CPI | multi-phase
Net Weight
161 lb.; 73.0 kg
Gross Weight
340 lbs; 154 kg
Operating Position
Vertical, Base Down
Water and Forced Air
Maximum Overall Dimensions:
18.75 in; 47.62 cm
17.03 in; 43.26 cm
Maximum Operating Temperature,
Envelope and Ceramic/Metal Seals
Available Filament Power Connectors (not supplied with tube):
Filament Power/Water Connector (2 required):
Filament rf Connector (1 required):
Available Anode Cooling Water Connectors (not supplied with
Note: 2 connectors are required per tube
EIMAC SK-2322 or EIMAC SK-2323
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 : [email protected]
multi-phase cooled power tetrode 4cm2500kg
GROUNDED GRID - Drive Pulsed
For long pulse fusion applications or CW Service
(Class AB or B)
2.5 190 2500
20 8.0 kilovolts
5.8 10.1
1500 2000Vdc
1550 kW
138.0 Kw
3500 kW
# Average during the pulse
* Approximate
UNPACKING – To insure safety of the operator performing the work as well as preventing damage to the
tube, the following instructions should be followed:
1) Open the crate by removing the lid, first unlock-
ing the toggle bolts in 8 places.
2) Attach a lifting hoist to the lifting loop and raise
the tube slightly with mounting brackets attached to
support the weight of the tube.
3) Remove 8 bolts securing the mounting brackets
to the corners.
4) Using the hoist, lift the tube and place on blocks
or on a stand that supports its weight by the bottom
of the lower corona ring.
5) Remove the brackets from the tube.
HANDLING – This product contains a thoriatedtungsten filament, and although of a rugged mesh
design, it is relatively fragile and a tube should be
protected from shock and vibration. A lifting eye is
available at the center of the anode cooler and should
be used any time the tube is to be lifted for moving,
etc. A lifting device such as a chain hoist may be
employed to lift the tube and should be capable of
safely supporting the full weight of the tube (up to 200
lbs with cooling water in the anode cooler) and should
be operated with great care, especially when lowering the tube onto a resting place or into equipment. It is
recommended that a thick rubber mat or similar material be used to absorb any undue shock that may occur
if the tube is to be placed temporarily on a hard surface.
STORAGE – If a tube is to be stored as a spare it should
be kept in its shipping crate and all water should be
purged from the anode cooler and from the filament supports/connectors. The anode cooler can be drained by
inverting the tube. Water should be purged from the internal filament support structure by applying compressed
air to one of the filament coolant ports and it is important
to note that pressure during this process must be limited
to 2 Bar (29 psi). Under no circumstances should one attempt to use an unregulated air source for this procedure.
The tube should be stored with a portable VACION pump power supply connected to allow monitoring the vacuum tubes vacuum properties (see
section on VACION PUMP OPERATION for details.)
MOUNTING - The 4CM2500KG must be mounted vertically, base down. The full weight of the tube should rest on
the screen-grid contact flange at the base of the tube, and
all lifting of the tube should be done with the lifting eye
which is attached to the top of the anode cooling jacket.
ANODE COOLING - The anode is cooled by circulating
high velocity water near the boiling point through the
structure. The inlet and outlet connections are clearly
marked on top of the anode cooling jacket and it is important they be connected only as indicated. Multiphase
cooling provides efficient removal of heat from the anode
and assures additional capacity for temporary overloads.
Tube life can be seriously compromised by the condition
of the cooling water. If it becomes contaminated, deposits
will form on the inside of the water jacket causing localized
anode heating and eventual tube failure. To insure minimum electrolysis and power loss, the water resistance
at 25°C should always be one megohm per cubic centimeter or higher. The relative water resistance should be
periodically checked using readily available instruments.
High velocity water flow is required to maintain high
thermal efficiency; for this reason operation at lower anode dissipation using lower flow rates than
what is listed in the table on p.3 is not recommended.
Cooling water must be well filtered, with effectiveness the equivalent of a 100-mesh screen, to eliminate any solid material and avoid the possibility of
blockage of any cooling passages, as this would immediately affect cooling efficiency and could produce
localized anode overheating and failure of the tube.
Minimum water flow requirements for the anode
are shown in the table for an outlet water temperature not to exceed 100°C and inlet water temperature
at 49°C. System pressure should not exceed 100 psi.
Approx. Jacket
Press Drop
This cooling data is applicable to steady-state or transient anode dissipation. At significantly reduced anode
dissipation a lower flow rate may be permissible but using
the maximum flow rate will protect the tube from unforeseen events that may cause surges in anode dissipation.
multi-phase cooled power tetrode 4cm2500kg
The original shipping crate with the shock mounts and hardware should be retained in a dry place for future use such as
moving a tube over a considerable distance. Instructions
on affixing the shock mounts is included with each tube.
available on request and contains considerable detail on purity requirements and maintenance systems.
BASE COOLING - The tube base requires air cooling with a
minimum of 50 cfm of air at 50°C maximum at sea level, directed toward the base seal areas from a general purpose
fan. It should be noted that temperatures of the ceramic/
metal seals and the lower envelope areas are the controlling and final limiting factor. Temperature-sensitive paints
are available for use in checking temperatures in these
areas before equipment design and air-cooling requirements are finalized. EIMAC Application Bulletin AB-20,
covers this subject in detail and is available on request.
Water cooling of the filament and screen grid supports
is also required, with inlet water temperature not to exceed 49°C. Each of the two filament connectors include
both an inlet and an outlet line, with the proper connector for the inlet water shown on the tube outline drawing. Minimum flow for the F1 connector is 2.0 gpm, at
an approximate pressure drop of 12 psi. Minimum flow
for the F2 connector is 4.0 gpm, at an approximate pressure drop of 50 psi. The screen grid cooling water is
fed by means of 1/4-18 NPT tapped holes shown on the
tube outline drawing, with a minimum flow of 2.0 gpm
required, at an approximate pressure drop of 12 psi.
multi-phase cooled power tetrode 4cm2500kg
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. These
ratings are limited values outside which serviceability of
the tube may be impaired. 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 by exceeded under any
usual conditions of supply-voltage 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.
During periods of standby service, filament life may be
increased by a small reduction in filament voltage. Black
heat operation (a reduction of filament voltage to 50% or
less of nominal voltage) is prohibited. During standby
periods, forced air cooling and water flow must be maintained on the filament supports to ensure the ceramic/
metal seal temperature does not exceed 200°C. In addition, anode cooling water flow must be maintained at a
rate that ensures the outlet water temperature never exceeds 100°C. See cautionary information regarding hot
water on p.5. Serious damage and personal harm can result if water flow is interrupted while power is applied to
the filament therefore system interlocks are necessary to
remove all power to the tube if coolant flow is not present
for any reason. Filament voltage should be measured at
the tube base, using an accurate rms-responding meter.
Where hum is an important system consideration, it
is permissible to operate the filaments with dc rather
than ac power. Contact CPI Microwave Power Products, EIMAC Operation Application Engineering for
special precautions when using a dc filament supply.
HIGH VOLTAGE - Normal voltages used with this tube
are deadly, and equipment must be designed properly
and operating precautions followed. Design all equipment so that no one can come in contact with high voltages. Equipment must include safety enclosures for
the high-voltage circuits and terminals, with interlock
switches to open primary circuits of the power supply and to discharge high voltage capacitors when access doors are opened. Interlock switches must not be
bypassed to allow operating with access doors open.
Always remember that HIGH VOLTAGE CAN KILL.
Care should be exercised to keep any rf power out of the
filament of the tube, as this can cause excessive operating temperatures. Both sides of the filament must be
bypassed to assure monopotential operation. It should
be ascertained that no resonance exists in the filament
circuit which could be excited during operation. When
this tube is operated at combined screen and grid dissipations above 10 kilowatts the filament power should
be reduced to maintain proper filament temperature (i.e.,
resistance) and thereby assure optimum life. Contact
CPI Microwave Power Products, EIMAC Operation Applications Engineering for specific recommendations.
FILAMENT OPERATION - Filament turn-on and turnoff should be programmed. Filament voltage should be
smoothly increased from zero to the operating level over
a period of two minutes, and a motor-driven continuously
variable auto-transformer (such as a VARIAC ® or a POWERSTAT®) is suggested. Inrush current must never be allowed to exceed twice normal operating current. Normal
turnoff procedure should be a smooth decrease from the
operating voltage to zero over a period of two minutes.
This tube is designed for commercial service, with only one
off/on filament cycle per day. If additional on/off cycling of
filament power is anticipated it is recommended the user
contact CPI Microwave Power Products, EIMAC Operation Applications Engineering for additional information.
VACION® PUMP OPERATION – The tube is supplied with
an ion pump and magnet, permanently mounted on the
filament structure at the base (stem). The primary func-
tion of this device is to allow monitoring of the condition
of the tube vacuum, as shown by an ion current meter.
With an operational tube it is recommended the VAC-ION
pump be operated full time so tube vacuum may be monitored on a continuous basis. A reading of less than 10
uAdc should be considered as normal, indicating excellent tube vacuum. In addition to other interlock circuitry
it is recommended that full advantage be taken of the
VACION pump readout by providing circuitry which will
shut down all power to the tube in the event the readout
current exceeds 50 uAdc. In the event of such a shutdown, the VACION pump should be operated alone until vacuum recovery is indicated by a reading of 10 uAdc
or less, at which point the tube may again be made operational. If the vacuum current rises again it should be
considered as indicating a circuit problem such as some
tube element may be over-dissipating and outgassing.
The VACION pump requires a positive voltage applied to
the center pin of approx. 3000 Vdc to operate properly.
One source for VACION power supplies is Varian, Inc.
Varian’s web site www.varianinc.com has several models
which may be suitable for use with the 4CM2500KG. Varian model 9290200 (120 volt ac line) or 9290201 (220 Volt
ac line) appear suitable. Alternatives for Varian power
supplies are: HeatWave Labs http://www.cathode.com/
and Duniway Stockroom http://www.duniway.com/
At the tetrode a coaxial cable is attached to the VACION
pump and comes attached to the tube as delivered. This
cable assy. includes a resistor that prevents the filament
current from being shorted to ground. The end of the resistor has a solder lug that is attached using one of the small
screws to the magnet assy at the VACION pump. The other
end of this cable has a female receptacle (type MHV, also
designated mil. UG-1016A/U or Amphenol type 27075).
To plug onto this receptacle a male plug type UG-932/U,
also supplied with each tube, is normally used for making up an extender cable of the required length. The
other end of the extender cable goes to the VACION
power supply; the Varian supplies require a Kings plug
1065-1 (not supplied with the 4CM2500KG). For info see:
http://www.kingselectronics.com/ and cable type RG58A/U or Belden 8259 is recommended for this connector.
In the case of a tube being held as a spare, it is recommended the VACION pump be operated continuously if
possible, otherwise it should be operated periodically to
check the condition of tube vacuum and operated as long
as necessary to achieve a reading of 10 uAdc or lower.
Figure 1 shows the relationship between tube vacuum and the ion current reading. Electrode voltages,
including filament voltage, should never be applied
if a reading of 50 uAdc or higher is obtained. In the
event that poor vacuum cannot be improved by operation of the VACION pump the user should contact
CPI Microwave Power Products, EIMAC Operation
and review the details with an Applications Engineer.
If the tetrode is grid-driven the cathode (and therefore
the filament power supply) is generally referenced to dc
ground potential, that is no bias voltage or other voltage
is supplied to the filament. In this case the VACION power supply may be used with no isolation and the shield
and connector on the VACION cable should be grounded
for reasons of electrical safety. If however the tetrode
is to be used in grounded-grid (cathode-driven) configuration as is typical in the case of VHF, then rf drive
applied to the tube’s cathode/filament will also be present on the VACION cable and therefore good rf isolation
must be provided to prevent rf power from flowing on
this cable. The system designer must therefore incorporate rf filtering on the VACION cable to keep rf energy from passing back into the VACION power supply
and its metering circuit; ferrite chokes around the cable
may be suitable. The filament supply should be grounded as any dc voltage that is applied from the filament
to ground will interfere with proper VACION operation.
cooled power tetrode 4cm2500kg
CPI | multi-phase
ANODE OPERATION - The maximum anode dissipation rating of 2500 kilowatts should not be exceeded
even for very brief periods during setup or tuning.
Anode current which flows at high anode voltages with
no rf, such as interpulse idling current, must be avoided
CPI | multi-phase cooled power tetrode 4cm2500kg
by such means as reducing screen voltage or increasing control grid bias during the “idling” period. Current
flowing at high anode voltage causes significant X-Ray
generation. At typical Class AB idling currents X-Ray
intensity is very high and represents a significant potential hazard to personnel in the vicinity of the tetrode.
See X-RADIATION HAZARD on p.7 for more information.
Operation with low values of anode current under some
conditions of high instantaneous anode voltage (such
as regulator service or lower power and low impedance
“tuning” conditions) can, as a result of the screen and
grid voltages chosen, lead to anode damage and subsequent failure from spot heating as a result of focusing
effects in the tube. If operation under such conditions
is necessary CPI Microwave Power Products, EIMAC
Operation’s Application Engineering should be contacted for assistance in selection of operating parameters.
GRID OPERATION - The maximum grid dissipation is
8 kilowatts and protective measures should be taken to
insure that this rating is not exceeded. Grid dissipation
is approximately equal to the product of dc grid current
and peak positive grid voltage. A protective spark gap
device should be connected between the control grid
and the cathode to guard against excessive voltage.
Under some operating conditions the control grid may exhibit a negative resistance characteristic. This may occur with high screen voltage when increasing the drive
power results in a net decrease in grid current. Large
values of negative grid current can cause the amplifier to
become regenerative. The driver stage must be designed
to tolerate this condition. One technique is to swamp the
driver so that the change in load, due to secondary grid
emission, is a small percentage of the total driver load.
SCREEN OPERATION - The maximum screen grid dissipation is 20 kilowatts. With no ac applied to the screen
grid, dissipation is simply the product of dc screen voltage and the dc screen current. Rf heating of the screen
must be measured in calculating total screen dissipation at frequencies greater than 60 MHz. 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. Suitable
protective circuitry must be provided to remove screen
power in case of a fault condition. A protective sparkgap device should be connected between screen grid
and the cathode to guard against excessive voltage.
Operation of the 4CM2500KG at its maximum VHF power
capabilities will result in sufficient rf current screen grid
heating to cause significant reverse screen grid current due to thermionic emission. Such operation will not
cause tube damage if proper procedures are followed;
however, the screen grid circuit must be designed with
this characteristic in mind so that the correct operating
voltage will be maintained on the screen under all conditions. Dangerously high anode current may flow if the
screen power supply exhibits a rising voltage characteristic with negative screen current. A current path from
the screen to cathode must be provided by a bleeder resistor to absorb the reverse current without allowing the
screen grid voltage to rise excessively. A series-regulated
power supply can only be used when an adequate bleeder resistor is provided; a shunt-regulated power supply
is also very effective towards meeting this requirement.
PULSE OPERATION - The thermal time constants of the
internal tube elements vary from a few milliseconds in
the case of the grids to about 200 milliseconds for the anode. In many applications the meaning of duty as applied
to a pulse chain is lost because the interpulse period is
very long. For pulse lengths greater than 10 milliseconds,
where the interpulse period is more than 10 times the pulse
duration, the element dissipations and required cooling
are governed by the watt-seconds during the pulse. Provided the watt-seconds are less than the listed maximum
dissipation rating and sufficient cooling is supplied, tube
life will not be compromised. To maintain high cooling efficiency the anode water flow must be sufficient to insure
turbulent flow. See Flow Recommendation on Page 3.
FAULT PROTECTION - In addition to the normal anode
over-current interlock and coolant interlock, the tube must
be protected from internal damage caused by any arc
which may occur. A protective resistance should always
be connected in series with the grid and anode to help absorb power supply stored energy if an arc should occur.
As noted under GRID OPERATION and SCREEN OPERATION, a protective spark gap should be connected from the
control grid to ground and from the screen grid to ground.
CPI Application Bulletin #17 titled FAULT PROTECTION
contains considerable detail and is available on request.
LOAD VSWR - The load VSWR should be monitored and
the detected signal used to operate the interlock system to
remove anode voltage within 20 milliseconds after a fault
occurs. In the case of high stored energy in the load system,
care must be taken to avoid excessive return energy from
damaging the tube and associated circuit components.
MODE SUPPRESSION CONSIDERATIONS - Highperformance high-power gridded tubes including the
4CM2500KG have natural circular resonance modes of
oscillation which must be suppressed during initial testing of equipment. The short compact stem structure of
EIMAC tubes provides easy access for mode suppression techniques. It is recommended that short pulse testing be used to detect this phenomenon and to evaluate
the effectiveness of the suppression techniques used.
The 4CM2500KG has been found to exhibit circular
mode oscillations in both L band and S band frequency
ranges. These modes must be suppressed externally to
prevent damage to the tube and to provide stable operation in the intended application. One technique which
has worked to suppress these circular modes is using
ferrite tiles. The ferrite tiles can be cemented (using
General Electric RTV-102 or equivalent) to the conical
and flat surfaces of the “screen deck” at the base of the
tube. The size of the tiles can be up to approximately
one inch square or rectangular and 0.1 to 0.3 inch thick.
The ferrite must have properties such that it is not
lossy at the fundamental frequency otherwise exces-
sive heating of the ferrite may occur. One source for
the ferrite material is: National Magnetics Group, Inc.
in Bethlehem, PA, USA. For further information contact CPI Microwave Power Products, EIMAC Operation.
In some instances, a compromise between tube efficiency and anode load impedance by way of modifying the output matching tuning and loading will
prevent circular mode oscillations from occurring
while a tube is delivering peak output. Adjustment of
both the screen voltage and grid bias voltage while
testing for circular mode oscillations is also predicated and fine adjustments in both parameters will
often reduce or eliminate circular mode oscillations.
multi-phase cooled power tetrode 4cm2500kg
An electronic crowbar, which will discharge power supply capacitors in a few microseconds after the start of an
arc, is required. The protection criteria for each supply is
to short each electrode to ground, one at a time, through a
vacuum relay switch and a 6-inch length of #30 AWG copper wire. The wire will remain intact if criteria are met.
X-RADIATION HAZARD - High-vacuum tubes operating
at voltages higher than 15 kilovolts produce progressively more dangerous X-ray radiation as the voltage is
increased. This tube, operating at its rated voltages and
currents, is a potential X-ray source. Only limited shielding is afforded by the tube envelope. Moreover, the Xradiation level may increase significantly with tube aging
and gradual deterioration, due to leakage paths or emission characteristics as they are affected by the high voltage. X-ray shielding may be required on all sides of tubes
operating at these voltages to provide adequate protection throughout the life of the tube. Periodic checks
on the X-ray level should be made, and the tube should
never be operated without required shielding in place. If
there is any question as to the need for or the adequacy
of shielding, an expert in this field should be contacted
to perform an X-ray survey. In cases where shielding
has been found to be required, operation of equipment
with interlock switches “cheated” and cabinet doors
open in order to be better able to locate an equipment malfunction can result in serious X-ray exposure.
strong rf fields even at relatively low frequency. Absorption
of rf energy by human tissue is dependent on frequency.
OSHA (Occupational Safety and Health Administration)
recommends that prolonged exposure to rf radiation
should be limited to 10 milliwatts per square centimeter.
multi-phase cooled power tetrode 4cm2500kg
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 from the tube terminals and
associated wiring. To control the actual capacitance
values within the tube, as the key component involved,
the industry and military services use a standard test
procedure described in Electronic Industries Association Standard RS-191. The test is performed on a cold
tube, and in the case of the 4CM2500KG, with no special
shielding. Other factors being equal, controlling internal tube capacitance in this way normally assures good
interchangeability of tubes over a period of time. The
capacitance values shown in the test specification or technical data are taken in accordance with Standard RS-191.
The equipment designer is cautioned to make allowance for the capacitance values, including tube-to-tube
variation and strays, which will exist in any normal application. Measurements should be taken with 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 different from those
listed here, write to CPI Microwave Power Products, EIMAC Operation ATTN: Applications Engineering; 607 Hansen Way, Palo Alto, CA 94304 USA.
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 or are exposed to power tubes or equipment which utilizes such tubes must take precautions
to protect themselves against possible serious bodily injury. Do not be careless around such products.
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.
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
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).
multi-phase cooled power tetrode 4cm2500kg
multi-phase cooled power tetrode 4cm2500kg
multi-phase cooled power tetrode 4cm2500kg
multi-phase cooled power tetrode 4cm2500kg
multi-phase cooled power tetrode 4cm2500kg
multi-phase cooled power tetrode 4cm2500kg