The 7203/4CX250B and 8621/4CX250FG are ceramic/metal forced-air cooled, external-anode radial-beam tetrodes with a maximum plate dissi- pation rating of 250 watts and a maximum input-power rating of 500 watts. The 7203/4CX250B is designed to operate with a heater voltage of 6.0 volts, while the 8621/4CX250FG is designed for operation at a heater volt- age of 26.5 volts. Otherwise, the two tube types have identical charac- teristics. GENERAL CHARACTERISTICS' ELECTRICAL Cathode: Oxide Coated, Unipotential Heater: Voltage (4CX250B) 6.0 + 0.3 V Current, at 6.0 volts.................... 2.6 A Cathode-Heater Potential, maximum +150 V Heater: Voltage (4CX250FG) .. 26.5 + 1.3 V Current, at 26.5 volts................... 0.54 A Cathode-Heater Potential,maximum.......... +150 V Amplification Factor (Average): Grid to Screen............................. 5 Direct Interelectrode Capacitances (Grounded cathode )2 Input 15.7 pF Output............................ þ þ þ þ..... þ þ.......... 4.5 pF Feedback.......................................... 0.04 pF Direct Interelectrode Capacitances (grounded grid and screen)~ Input 13 pF Output................................................ 4.5 pF Feedback.............................................. 0.01 pF Frequency of Maximum Rating: CW................... þ þ þ þ þ 500 MHz 1. Characteristics and operating values are based upon performance tests. These figures may change without notice as the result of additional data or product refinement. EIMAC Division of Varian should be consulted before using this information for final equipment design. 2. In Shielded Fixture. MECH AN I CA L Maximum Overall Dimensions: Length þ þ þ þ þ þ þ þ þ 2.46 in; 62.5 mm Diameter þ þ þ þ þ þ þ þ þ þ ~0 þ þ þ þ þ þ 1.64 in; 41.7 mm Net Weight............... þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ 4 oz; 113 gm Operating Position....................... þ þ þ þ þ þ þ Any (Revised 8-1-74) @ 1962, 1970, 1973, 1974 Varian Printed in U.S.A. EIMAC division of varian / 301 industrial way / san carlos / california 94070 Maximum Operating Temperature: Ceramic/Metal Seals........................ 250§C þ þ þ þ þ þ þ þ þ 250§ C Anode Core.... þ þ þ þ Cooling þ þ ................... Forced Air Base....................................... .. Special 9-pin JEDEC-B8-236 Recommended Socket EIMAC SK-600 Series Recommended Chimney þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ EIMAC SK-600 Series RADIO FREQUENCY LINEAR AMPLIFIER TYPICAL OPERATION (Frequencies to 175 MHz) GRID DRIVEN (SSB) Class AB1, Grid Driven, Peak Envelope or Modulation Crest Conditions Class AB1 Plate Voltage........... 1000 1500 2000 Vdc Screen Voltage.......... 350 350 350 Vdc MAXIMUM RATINGS Grid Voltage 1........... -55 -55 -55 Vdc Zero-Signal Plate Current.... 100 100 100 mAdc DC PLATE VOLTAGE............ 2000 VOLTS Single Tone Plate Current 250 250 250 mAdc DC SCREEN VOLTAGE........... 400 VOLTS Two-Tone Plate Current..... 190 190 190 mAdc DC GRID VOLTAGE -250 VOLTS Single-Tone Screen Current2 .. 10 8 5 mAdc DC PLATE CURRENT............ 0.25 AMPERE Two-Tone Screen Current2... 2 -1 -2 mAdc PLATE DISSIPATION............ 250 WATTS Single-Tone Grid Currents... 0 0 0 mAdc SCREEN DISSIPATION........... 12 WATTS Peak rf Grid Voltage2..... 50 50 50 V GRID DISSIPATION 2 WATTS Plate Output Power 120 215 300 W Resonant Load impedance 2000 3000 4000 ohms 1. Adjust to specified zero-signal dc plate current. 2. Approximate value. RADIO FREQUENCY LINEAR AMPLIFIER TYPICAL OPERATION (Frequencies to 175 MHz) GRID DRIVEN, CARRIER CONDITIONS Class AB1, Grid Driven Class AB1 Plate Voltage............ 1000 1500 2000 Vdc Screen Voltage.... 350 350 350 Vdc Grid Voltage 1.......:,... -55 -55 -55 Vdc MAXIMUM RATINGS 100 mAdc Zero-Signal Plate Current 100 100 150 mAdc Carrier Plate Current....... 150 150 -4 mAdc DC PLATE VOLTAGE............ 2000 VOLTS Carrier Screen Current...... 3 25 v DC SCREEN VOLTAGE 400 VOLTS Peak rf Grid Voltage2....... 25 25 65 W DC GRID VOLTAGE -250 VOLTS Plate Output Power 30 50 DC PLATE CURRENT............ 0.25 AMPERE PLATE DISSIPATION........... þ 250 WATTS 1, Adjust to specified zero-signal dc plate current SCREEN DISSIPATION........... 12 WATTS 2. Approximate value. GRID DISSIPATION 2 WATTS RADIO FREQUENCY POWER AMPLIFIER TYPICAL OPERATION(Frequencies to 175 MHz) 500 MHz~ OR OSCILLATOR Plate Voltage....... 500 1000 1500 2000 2000 Vdc Class C Telegraphy or FM Telephony Screen Voltage 250 250 250 250 300 Vdc (Key-Down Conditions) Grid Voltage....... -90 -90 -90 -90 -90 Vdc Plate Current....... 250 250 250 250 250 mAdc Screen Current 1..... 45 38 21 19 10 mAdc2 MAXIMUM RATINGS Grid Currentl....... 35 31 28 26 10 mAdc2 Peak rf Grid Voltagel.. 114 114 112 112 V Measured Driving DC PLATE VOLTAGE....... þ þ þ þ þ 2000 VOLTS Power 1....,....... 4.0 3.5 3.2 2.9 W DC SCREEN VOLTAGE..... þ þ þ .. þ 300 VOLTS Plate Input Power .... 125 250 375 500 500 W DC GRID VOLTAGE -250 VOLTS Plate Output Power... 70 190 280 390 290 W DC PLATE CURRENT....... þ þ . þ þ 0.25 AMPERE Heater Voltage PLATE DISSIPATION 250 WATTS (4CX250B) 6.0 6.0 6.0 6.0 5.5 V 12 WATTS Heater Voltage 2 WATTS (4CX250FG) 26.5 26.5 26.5 26.5 24.3 V SCREEN DISSIPATION GRID DISSIPATION 1. Approximate value. 2. Measured values for a typical cavity amplifier circuit. 2 PLATE MODULATED RADIO FREQUENCY POWER TYPICAL OPERATION (Frequencies to 175 MHz) ANPLIFIER-GRID DRIVEN Class C Telephony (Carrier Conditions) Plate Voltage............ 500 1000 1500 Vdc Screen Voltage........... 250 250 250 Vdc MAXIMUM RATINGS Grid Voltage............ -100 -100 -100 Vdc DC PLATE VOLTAGE........... 1500 VOLTS Plate Current.........., . 200 200 200 mAdc DC SCREEN VOLTAGE.......... 300 VOLTS Screen Current........... 31 22 20 mAdc DC GRID VOLTAGE -250 VOLTS Grid Current 15 14 14 mAdc DC PLATE CURRENT........... 0.20 AMPERE Peak rf Grid Voltage....... 118 117 117 v PLATE DISSIPATION1'...... 165 WATTS Calculated Driving Power.... 1.8 1.7 1.7 W SCREEN DISSIPATION2........ 12 WATTS Plate Input Power......... 100 200 300 W GRID DISSIPATION2........... 2 WATTS Plate Output Power........ 60 145 235 W 1. Corresponds to 250 watts at 100% sine-wave modu- lation. 2. Average, with or without modulation. 3. Approximate value. AUDIO FREQUENCY POWER AMPLIFIER TYPICAL OPERATION (Two Tubes) OR MODULATOR Class AB, Grid Driven (Sinusoidal Wave) Plate Voltage......... .. 1000 1500 2000 Vdc Screen Voltage........ 350 350 350 Vdc Grid Voltagel/3....... -55 -55. -55 Vdc MAXIMUM RATINGS (Per Tube) Zero-Signal Plate Current 200 200 200 mAdc Max Signal Plate Current 500 500 500 mAdc DC PLATE VOLTAGE 2000 VOLTS Max Signal Screen Current 1... 20 16 10 mAdc DC SCREEN VOLT AGE........ 400 VOLTS Max Signal Grid Currentl. 0 0 0 mAdc DC GRID VOLTAGE............. -250 VOLTS Peak af Grid Voltages .. 50 50 50 V DC PLATE CURRENT............. 0.25 AMPERE Peak Driving Power 0 0 0 W PLATE DISSIPATION 250 WATTS Plate Input Power 500 750 1000 W SCREEN DISSIPATION 12 WATTS Plate Output Power 240 430 600 W GRID DISSIPATION 2 WATTS Load Resistance (plate to plate) .. 3500 6200 9500 0 1. Approximate value. 2. Per Tube. 3. Adjust to give stated zero-signal plate current. NOTE: TYPICAL OPERATION data are obtained from direct measurement or by calculation from published character- istic curves. Adjustment of the rf grid voltage to obtain the specified plate current at the specified bias, screen and plate voltages is assumed. If this procedure is followed, there will be little variation in output power when the tube is changed, even though there may be some variation in grid and screen current. The grid and screen currents which result when the desired plate current is obtained are incidental and vary from tube to tube. These current variations cause no difficulty so long as the circuit maintains the correct voltage in the presence of the variations in current. In the case of Class C Service, if grid bias is obtained principally by means of a grid resistor, the resistor must be adjustable to obtain the required bias voltage when the correct rf grid voltage is applied. RANGE VALUES FOR EQUIPMENT DESIGN Min. Nom. Max. Heater: 4CX250B Current at 6.0 volts 2.3 2.9 A Heater: 4CX250FG Current at 26.5 volts þ þ þ þ þ þ þ þ þ 0.45 0.62 A Cathode Warmup Time ......................... þ þ þ þ þ þ 30 60 sec. Interelectrode Capacitances1 (grounded cathode connection) Input.................................. þ þ þ þ þ þ þ 14. 2 17.2 pF Output................... þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ 4.0 5.0 pF ' Feedback................. 0.06 pF Interelectrode Capacitancesl (grounded grid and screen) Input.................... þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ 13.0 pF Output.................... þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ þ 4.0 5.0 pF i Feedback .................. þ þ þ þ þ 0.01 pF 1 Cout values shown are for 4CX250B; for 4CX250FG, values are............ 4.0 --- 5.3 pF 3 4CX250B-4CX250FG APPLICATION MECHANICAL ELECTRICAL MOUNTING - The 4CX250B and 4CX250FG may HEATER - The rated heater voltage for the be operated in any position. An EIMAC Air-System 4CX250B and 4CX250FG is 6.0 volts and 26.5 Socket, SK-600 series, or a socket having equiv- volts, respectively, and the voltage should be alent characteristics, is required. Sockets are maintained as closely as practicable. Short-time available with or without built-in screen cap- changes of + 10% will not damage the tube, but acitors and may be obtained with either grounded variations in performance must be expected. The or ungrounded cathode terminals. heater voltage must be maintained within + 5% to minimize these variations and to obtain maximum COOLING - Sufficient forced-air cooling must be tube life. provided for the anode, base seals, and body At frequencies above approximately 300 MHz seals to maintain operating temperatures below transit-time effects begin to influence the cath- the rated maximum values. Air requirements to ode temperature. The amount of driving power maintain anode core temperatures at 200C with diverted to heating the cathode by back-bombard- an inlet air temperature of 50C are tabulated ment will depend upon frequency, plate current, below. These requirements apply when a socket and driving power. When the tube is driven to of the EIMAC SK-600 series and an EIMAC SK-606 maximum input as a class-C amplifier, the heater chimney are used with air flow in the base to voltage should be reduced according to the table anode direction. below; Frequency MHz 4CX250B 4CX250FG SEA LEVEL 10,000 FEET Plate Air Flow Pressure Air Flow Pressure 300 and lower 6.00 volts 26.5 volts Dissipa- (CFM) Drop( In.of (CFM) Drop(In.of 301 to 400 5.75 volts 25.3 volts tion(watts ) water) water) 401 to 500 5.50 volts 24.3 volts 200 5. 0 0.52 7.3 0.76 250 6.4 0.82 9.3 1 20 CATHODE OPERATION - The oxide coated unipotential cathode must be protected against The blower selected in a given application excessively high emission currents. The maxi- must be capable of supplying the desired airflow mum rated dc input current is 200 mA for plate- at a back pressure equal to the pressure drop modulated operation and 250 mA for all other shown above plus any drop encountered in ducts types of operation except pulse. and filters. The blower must be designed to de- The cathode is internally connected to the liver the air at the desired altitude. four even-numbered base pins and all four of the At 500 MHz or below, base cooling air re- corresponding socket terminals should be used quirements are satisfied automatically when the to make connection to the external circuits. At tube is operated in an EIMAC Air-System Socket radio frequencies it is important to keep the and the recommended air flow rates are used. cathode leads short and direct and to use con- Experience has shown that if reliable long life ductors with large areas to minimize the induc- operation is to be obtained, the cooling air flow tive reactances in series with the cathode leads. must be maintained during standby periods when It is recommended that rated heater voltage be only the heater voltage is applied to the tube. applied for a minimum of 30 seconds before other The anode cooler should be inspected periodic- operating voltages are applied. Where the circuit ally and cleaned when necessary to remove any design requires the cathode and heater to be op- dirt which might interfere with effective cooling. erated at different potentials, the rated maximum heater-to-cathode voltage is 150 volts regardless VIBRATION - These tubes are capable of satis- of polarity. factorily withstanding ordinary shock and vi- bration, such as encountered in shipment and GRID OPERATION - The maximum rated dc normal handling. The tubes will function well in grid bias voltage is -250 volts and the maximum automobile and truck mobile installations and grid dissipation rating is 2.0 watts. In ordinary similar environments. However, when shock and audio and radio-frequency amplifiers the grid vibration more severe than this are expected, dissipation usually will not approach the max- it is suggested that the EIMAC 4CX300A or imum rating. At operating frequencies above the 4CX250R be employed. 100 MHz region, driving-power requirements for 4CX250B-4CX250F G amplifiers increase noticeably. At 500 MHz as Self-modulation of the screen in plate-mod- much as 20 watts of driving power may have to ulated tetrode amplifiers using these tubes may be supplied. However, most of the driving power not be satisfactory because of the screen-voltage is absorbed in circuit losses other than grid dis- screen-current characteristics. Screen modulation sipation, so that grid dissipation is increased from a tertiary winding on the modulation trans- only slightly. Satisfactory 500 MHz operation of former or by means of a small separate modulator the tube in a stable amplifier is indicated by tube will usually be more satisfactory. Screen- grid-current values below approximately 15 mA. voltage modulation factors between 0.75 and 1.0 The grid voltage required by different tubes will result in 100% modulation for plate-modulated may vary between limits approximately 20% above rf amplifiers using the 4CX250B or 4CX250FG. and below the center value, and means should be provided in the equipment to accommodate such PLATE OPERATION - The maximum rated variation. It is especially important that varia- plate dissipation power is 250 watts. In plate- tions between individual tubes be compensated modulated applications the carrier plate dissi- when tubes are operated in parallel or push-pull pation power must be limited to 165 watts to circuits, to assure equal load sharing. avoid exceeding the plate dissipation rating with The maximum permissible grid-circuit re- 100% sine wave modulation. The maximum dis- sistance per tube is 100,000 ohms. sipation rating may be exceeded for brief periods during circuit adjustment without damage to the tube. SCREEN OPERATION - The maximum rated power dissipation for the screen is 12 watts"and MULTIPLE OPERATION - Tubes operating in the screen input power should be kept below that parallel or push-pull must share the load equally. level. The product of the peak screen voltage It is good engineering practice to provide indiv- and the indicated dc screen current approximates idual metering and individual adjustment of bias the screen input power except when the screen or screen voltage to equalize the inputs. current indication is near zero or negative. Where overload protection is provided, it In the usual tetrode amplifier, where no sig- should be capable of protecting the surviving nal voltage appears between cathode and screen, tube(s) in the event that one tube fails. the peak screen voltage is equal to the dc screen VHF OPERATION-The 4CX250B and 4CX250FG voltage. are suitable for use in the VHF region. Such op- When signal voltages appear between screen eration should be conducted with heavy plate and cathode, as in the case of screen-modulated loading, minimum bias, and the lowest driving amplifiers or cathode-driven tetrode amplifiers, power consistent with satisfactory performance. the peak screen-to-cathode voltage is the sum of It is often preferable to operate at a sacrifice in the dc screen voltage and the peak ac or rf efficiency to obtain increased tube life. signal voltage applied to scgeen or cathode. HIGH V 0 L T A G E - The 7203/4CX250B and Protection for the screen should be provided 8621/4CX250FG operate at voltages which can by an over-current relay and by interlocking the be deadly, and the equipment must be designed screen supply so that plate voltage must be ap- properly and operating precautions must be fol- plied before screen voltage can be applied. lowed. Equipment must be designed so that no The screen current may reverse under certain one can come in contact with high voltages. All conditions and produce negative current indica- equipment must include safety enclosures for tions on the screen milliammeter. This is a nor- high-voltage circuits and terminals, with inter- mal characteristic of most tetrodes. The screen lock switches to open the primary circuits of the power supply should be designed with this char- power supplies and to discharge high-voltage acteristic in mind so that the correct operating condensers whenever access doors are opened. voltage will be maintained on the screen under Interlock switches must not be b y p a s s e d or all conditions. A current path from screen to "cheated" to allow operation with access doors cathode must be provided by a bleeder resistor, open. Always remember that HIGH VOLTAGE gaseous voltage regulator tubes, or an electron CAN KILL. tube shunt regulator connected between screen SPECIAL APPLICATIONS-If it is desired to op- and cathode and arranged to pass approximately erate these tubes under conditions widely differ- 15 milliamperes per connected screen. An elec- ent from those given here, write to Application tron tube series regulator can be used only when Engineering Dept., EIMAC Division of Varian, an a equate bleeder resistor is provided. San Carlos, Calif. 94070 for information and recommendations. 5