Eimac 3CX1500D7 Datasheet

TECHNICAL DATA

AIR-COOLED

HIGH-MU

POWER TRIODE

3CX1500D7

The Eimac 3CX1500D7 is a compact power triode with an anode dissipation rating of 1500 watts. This tube
features a filament designed to operate at 5 volts, a value that is common to other power grid tubes and allows
a single 3CX1500D7 to replace two 3-500Z in many applications. The high-Mu grid employed in this tube
permits operation as a linear amplifier in class AB with zero or minimal bias voltage. The 3CX1500D7 may also
be used in class B or C with additional bias voltage where it provides good efficiency, making it ideal as an rf
amplifier for industrial and scientific applications.

GENERAL CHARACTERISTICS

ELECTRICAL

Filament: Thoriated Tungsten

Voltage..................................…... 5.0

Current @ 5.0 volts…………................… 30 A

Direct Interelectrode Capacitances (grounded grid)

Cin.................................................…….. 18.6 pF

Cout............................................……… 7.2 pF

Cpk..................................................…… 0.4 pF

Amplification Factor, Average….................…200

Frequency of Maximum Rating (CW).......... 100 MHz

± 0.25 V

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MECHANICAL

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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 Eimac Division 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.

Overall Dimensions:

Length ................................….. 5.6 in; 143 mm

Diameter ……………..……….... 3.42 in; 86.9

mm

Weight (approx.) ....................……. 2.4 lb; 1.1 kg

Operating Position...............Vertical, base up or down

Maximum Operating Temperatures:

Ceramic/Metal Seals & Envelope............... 250°C

Anode Core ……………………………….…250°C

Cooling ........................................………. Forced Air

Base................................................. Special, Five

Pin
Recommended Socket …….…………EIMAC SK–410

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3CX1500D7

RADIO FREQUENCY LINEAR AMPLIFIER
Class AB2, Cathode-Driven

ABSOLUTE MAXIMUM RATINGS:

Anode Voltage............……….. 6.0 Kilovolts dc

Anode Current............………... 0.8 Ampere dc

Anode Dissipation.................... 1.5 Kilowatts

Grid Voltage……………………-500 Volts dc

Grid Dissipation ..................… 50 Watts

TYPICAL OPERATION*, under 30 MHz:

Anode Voltage...................... 3.0 4.5 kVdc

Cathode Bias Voltage............. 0 12 Vdc

Zero-Signal Anode Current . 168 98 mAdc
Anode Current (max signal) 0.72 0.64 Adc
Grid Current*
Driving Power*
Anode Dissipation*
Anode Output Power*

1...................................

1....................................

1 ......................

1................

247 180 mAdc

80 70 W

660 930 W

1.5 1.95 kW

Input Impedance.................... 73 72 Ohms

Resonant Anode Load Z*.. 2650 2900 Ohms
Intermodulation Distortion
Products2 , 3rd order ... -29 -34 dB

5th order......-43 -37 dB

* Measured data

1. Approximate Values

2. Referenced against one tone of a two-equal tone signal

RADIO FREQUENCY POWER AMPLIFIER TYPICAL OPERATION, under 30 MHz:
Class B, Cathode-Driven

Anode Voltage....................................5.0 kVdc

ABSOLUTE MAXIMUM RATINGS: Anode Current.................................. 0.71 Adc

Cathode Bias Voltage.......................... 25 Vdc

Anode Voltage.............................6.0 Kilovolts dc Grid Current *

Anode Current.............................0.8 Ampere dc Driving Power*

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.................................. 0.20 Adc

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...................................95 W

Anode Dissipation .......................1.5 Kilowatts Anode Dissipation...........................1220 W

Grid Voltage…………………..… -500 Volts dc Anode Output Power....................... 2400 W

Grid Dissipation.............................50 Watts Input Impedance..................................85 Ohms

Resonant Anode Load Impedance.. 3760 Ohms

1. Approximate Values

NOTE: TYPICAL OPERATION data are obtained from direct measurement or by calculation from
published characteristic curves. Adjustment of the rf grid voltage 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.

RANGE VALUES FOR EQUIPMENT DESIGN

Min. Max.

Filament Current @ 5.0 Volts................................................................... 29.5 32 A

Interelectrode Capacitances

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(grounded grid)

Cin .............................................................................................….. 16.5 21 pF

Cout ................................................................................................ 5.8 8.9 pF

Cpk.................................................................................................. --- 0.6 pF

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Capacitance values are for a cold tube as measured in a shielded fixture in accordance with Electronic Industries Association

Standard RS-191.

Zero-Signal Anode Current (Ec = 0, Eb = 4.0 kV) ……………………… 0.305 0.375 A

Cut-off Bias (Eb = 3 kV, Ib = 1.0 mA) …………………………………. --- - 24.0 V

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3CX1500D7

APPLICATION

HANDLING – This product contains a thoriated­tungsten filament and should be protected from
shock and vibration. It is recommended that the
tube be removed from equipment that is being
shipped, to prevent damage that may occur in
transit.

The center “pin” in the base of this tube is hollow
and is a part of the filament support structure and
is at the same potential as the filament; no
electrical contact to this pin is necessary or
desirable. The vacuum “nip-off” or seal is located
at the end of this center “pin”; the edge on it is
very sharp and can cut. Do not touch or contact
this seal as any mechanical damage to it may
cause loss of vacuum integrity.

MOUNTING & SOCKETING – The tube must be
operated with its primary axis vertical. The base of
the tube may be up or down at the option of the
equipment designer. The Eimac SK-410 socket is
ideal for use with this tube; other sockets may
restrict airflow or increase pressure-drop and are
therefore not recommended. Sockets other than
the Eimac SK-410 may also apply excessive
lateral force to the connecting pins on the base,
and this can result in mechanical failure of the
metal/ceramic seals. An air chimney is necessary
to assure that air flows through the fins in the
anode cooler. A cylindrically-shaped Teflon™ or
Pyrex chimney around the outside of the cooler is
recommended for this purpose. Connection to the
anode should be made by use of a band around
the anode cooler.

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. Before storage a
new tube should be operated in the equipment for
100 to 200 hours to establish that it has not been
damaged and operates properly. If the tube is still
in storage 6 months later it should be operated in
the equipment for 100 to 200 hours to make sure
there has been no degradation. If operation is
satisfactory the tube can again be stored with
great assurance of being a known-good spare.

COOLING - The maximum temperature rating for
the anode core and the ceramic/metal seals of
this tube is 250°C and sufficient forced-air cooling
must be provided to assure operation at safe tube
temperatures. Tube life is usually prolonged if
cooling in excess of the absolute minimum
requirements is provided.

The table below shows minimum airflow require­ments necessary to keep the anode temperature
below 225°C with an inlet air temperature of 25°C
at sea level. Air-flow is specified to be in the base­to-anode direction. This data applies to operation
below 30 MHz; if the tube is used above this
frequency additional cooling may be required
because of increased rf losses that occur at VHF.

Airflow Anode Airflow Approximate

Direction Dissipation CFM Pressure Drop
Watts in H

Base to Anode 500 15 0.09
“ 1000 34 0.22
“ 1500 65 0.45

At higher altitudes increased airflow is required; in
this case both the airflow and pressure drop
values shown must be increased by the following
factors: 5000 feet x 1.24; 10,000 feet x 1.46.
Additional cooling of the tube base may be
required especially if the anode cooling air is not
directed past the base first. The preferred
configuration is airflow supplied in the base-to­anode direction; cooling air may be supplied in the
alternate direction, but the flow rate must be
substantially higher to provide proper cooling.

The designer is cautioned that the cooling
recommendations shown are absolute values for
inlet air and temperature rise conditions shown
with no safety factor; it is considered good
engineering practice to allow additional air flow for
conservatism and to make allowance for variables
such as dirty air filters, dirty anode cooling fins,
and pressure losses in air ducting; other factors
for additional airflow are the increased anode
temperature that occurs during adverse load
conditions and reduced anode efficiency that may
occur during amplifier tuning and loading.

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