MIL-PRF-1/1313G
TABLE I. Testing and inspection - Continued.
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At frequencies above approximately 200 MHz, it may be necessary to reduce heater voltage to compensate for rf transit-time
heating of the cathode after dynamic operation of the tube has started. This back heating is a function of frequency, grid
current, grid bias, anode current, duty cycle, and circuit design and adjustment. Particular care should be used in the
selection of stable circuit components and in final tuning of high-frequency circuits as off-resonance operation, even to a small
degree, may result in marked and undesirable increase in cathode temperature. There is an optimum heater voltage which
will maintain the cathode at the correct operating temperature for any particular set of operating conditions. A maximum
variation of ± 5 percent from optimum is permitted. For straight-through, Class C CW amplifier operation, the following heater
operation voltages are indicated:
Frequency (MHz)
Ef (V ac)
201 to 300
5.75
301 to 400
5.50
401 to 500
5.00
When the tube is operated at 100 percent of maximum rated anode dissipation at an incoming air temperature of 25°C
2/
maximum, a minimum airflow of 5.0 cfm at sea level shall pass through the anode cooler. If the socket EIMAC SK-710 and
chimney SK-606, or equivalents, are used, an incoming airflow of 5.0 cfm to the lower end of the socket is required. At this
flow of 5.0 cfm, the static pressure drop directly across the tube and socket (with chimney installed) is approximately 0.4 inch
of water. This pressure drop varies with the amount of escaping air and with the shape and construction of the air director
(chimney). The airflow rating applies at bias voltages of less than 100 volts and frequencies less than 500 MHz. Air cooling
of the tube should be increased with increased negative grid bias, increased incoming air temperature, increased frequency of
operation, or a combination. In all cases of operation, a socket which provides forced-air cooling of the base shall be used,
and maximum seal and anode core temperature ratings shall not be exceeded. Airflow must be applied before or
simultaneously with electrode voltages, and may be removed simultaneously with them. In cases where long life and
consistent performance are factors, cooling in excess of minimum requirements is normally beneficial.
3/
Unless otherwise specified herein, in all electrical tests involving application of heater voltage, forced-air cooling of the tube is
allowed at the rate of 5.0 cfm for the base and anode. The tube should be operated in an air-system socket (EIMAC SK-710
socket, with EIMAC SK-606 chimney, or equivalents). Standard temperature and pressure conditions shall apply.
4/
This test is to be the first test performed at the conclusion of the holding period.
5/
Pulse emission (1) and (2) are taken at the voltage conditions specified. For the basic test circuit, see test method 1372,
figure 1372-1.
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Testing shall be performed every three months, with sampling as follows:
n1 = 4
c1 = 0
The listed tests shall be considered as nondestructive except in case of failure. In case of a sample failure, that test shall
become conformance inspection, part 2, acceptance level 6.5 of MIL-PRF-1 Table III, for three consecutive successful
submissions, at which time the test may revert to the quarterly basis.
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The fixture described in Drawing 284-JAN shall be used to hold the tube in the manner indicated. The test circuit shown on
figure 3 shall be used, but tubes found to electrically oscillate for causes other than vibration shall not be tested nor rejected
on this test. Each tube under test shall be subjected to one sweep cycle in each of the three axes X, Y, and Z. One sweep
cycle (100 to 750 Hz, ascending only) shall be covered in 6 to 12 minutes. Each tube shall be vibrated for 60 seconds at the
frequency which gives the maximum vibration output voltage in each of the three positions. If at the end of 60 seconds the
vibration output is increasing, the vibration shall be continued until there is no further increase for 60 seconds. The tubes
shall not show noise voltage output in excess of the maximum limit specified, except one intermittent short per tube shall be
allowable during this test. The tube shall show no intermittent or tap shorts after the test. In addition to reading noise voltage
output with a VTVM, such as an HP400D or equivalent, a permanent recording shall be made using a good quality recorder to
produce a plot of noise voltage versus frequency. Noise voltage amplifiers used with the recorder shall have a ± 1 dB
frequency response over the range to be measured (100 to 750 Hz) and the overall recording equipment shall be capable of
fast response in order to show sharp noise voltage spikes resulting from internal tube resonances or other phenomenon.
Prominent noise peaks indicated on the recording shall be individually investigated by fixed-frequency operation, and the 60-
second operation shall be made at the frequency of highest noise as so selected. The frequency at the extremes of the
sweep shall be read with an accuracy of ± 1 percent.
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