MIL-PRF-1/160N
TABLE I. Testing and Inspection. - Continued.
NOTES: - Continued.
2. Maximum life may be obtained by adjusting the heater voltage in accordance with the application. A table of heater
voltage verse frequency is presented as a guide.
Frequency (MHz)
Ef (V ac)
Up to 300
6.00
301 to 400
5.75
401 to 500
5.50
3. In all cases of electrical tests involving application of heater voltage, the socket on Drawing 246-JAN (see note 13) shall
be used. An incoming airflow of 6.0 cfm maximum to the grid end of the socket is permitted.
4. An infinite baffle system as shown on figure 2, or equal, with an airflow of 5.6 cfm at sea level shall be used. The static
pressure drop is measured across the tube and socket.
5. The forced-cooling test shall be made as follows:
At an ambient temperature of 25 °C, both the base and the anode shall be cooled by applying an airflow of 5.6 cfm
maximum, at sea level from a single source using the infinite baffle system as shown on figure 2, or equal.
At the specified test conditions, the anode core temperature, the anode seal temperature, and the base seal temperature
shall not exceed the specified limits.
All temperatures shall be measured by means of thermocouples located as follows:
Anode core: This thermocouple shall be embedded in the top of the cooler, with the anode dome removed, if necessary,
by means of drilling a small hole, shallow enough so that the tube vacuum shall not be lost, placing the welded
thermocouple junction therein, and then bending the edges of the hole in order to hold the thermocouple firmly in place.
Anode seal: This thermocouple shall be attached, using any appropriate material, to the surface of the metal immediately
above metal-to-dielectric seal.
Base seal: This thermocouple shall be attached, using any appropriate material, to the surface of the metal immediately
adjacent to the base dielectric material and at the immediate periphery of the dielectric material.
In all cases, good electrical continuity between the thermocouple and the metal area in close proximity must be
demonstrated before the cooling test can be performed.
6. This is a destructive test. Operate the tube in an upright position. Preheat the tube at specified test conditions for 1
minute. Remove airflow for 100 seconds. Restore airflow and after 1 minute perform the total grid current test. Any tube
which evidences a short or open circuit during this test will be considered a failure.
7. The maximum value of the voltage applied to the anode and grids shall not exceed 900 volts. The pulse duration
measured at 5 percent of the maximum value shall be not less than 3 microseconds (µs). At 50 percent amplitude, the
duration shall be less than 2 µs. The applied voltage shall have a maximum repetition rate such that the duty cycle,
based on the pulse length measured at 50 percent amplitude, shall not exceed 0.0002 (0.02 percent). An alternate
pulsing emission test may be used with the following conditions and limits:
Conditions
Parameter
Minimum
Maximum
is = 30 a , eb = ec1 = ec2
etd
---
850 v
For life-test end points, is = 21 a.
5
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