MIL-PRF-1/1670D
TABLE I. Testing and inspection - Continued.
1/
At frequencies above approximately 300 MHz under Class C telegraphy conditions, it may be necessary to reduce heater
voltage to compensate for RF transmit-time heating of the cathode. This type of back-heating is a function of frequency, grid
bias, anode current, duty cycle, and circuit design and adjustment. Heater voltage should be maintained within ± 5 percent
when long life and consistent performance are factors, but in no case shall the heater be operated at less than 5.4 volts. The
following heater operation voltages are for straight-through CW amplifier operation:
Ef (V)
Frequency
300 or lower
6.00
301 to 400
5.75
401 to 500
5.50
2/
Peak anode current (ib) may be considered as average during the pulse and shall be limited to 6.0 amperes. With a pulse
length (tp) longer than 80 µs or a duty ratio (Du) higher than 0.0016, peak anode current shall be reduced in accordance with
the data shown on figure 2.
3/
Forced-air cooling shall be provided for the base and anode. The maximum seal and anode core temperature rating should not
be exceeded. At an anode dissipation of 250 watts and an incoming air temperature of 50°C maximum at sea level, a
minimum airflow of 4.8 cfm shall pass through the anode cooler. With voltages applied to the tube, the static pressure drop
across the anode cooler with an airflow of 4.8 cfm at 50°C at seal is approximately .25 inch of water. The pressure drop varies
with the amount of escaping air, air temperature, and with the shape and construction of the air detector. The pressure drop in
most equipments can be expected to be considerably higher than .25 inch of water because of temperature and system losses
caused by associated hardware such as collets or cavity. The stem shall be cooled by a portion of the anode air or by a
separate air supply. Airflow should be applied before or simultaneously with electrode voltages (including the heater) 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.
4/
In all electrical tests involving applications of heater voltage, forced-air cooling of the tube shall be allowable at the rate of 4.8
cfm maximum, for the base and anode, at sea level. Cooling air shall not have a temperature less than 20°C.
5/
Test cavity in accordance with Drawing No. 2019229-0501 (The Bendix Corporation, Communications Division), or equivalent.
With the tube inserted in the cavity, a RF signal from a standard signal generator is coupled into the cavity by means of a small
loop. Signal is extracted from the cavity by means of another small loop, detected, and displayed on an HP-415-B, or
equivalent, standing-wave ratio indicator. The signal generator frequency is adjusted for maximum output after detection. The
frequency is then measured by means of a good quality wavemeter, such as the PRD Electronics Inc., Model 1587A, or
equivalent.
6/
Test cavity in accordance with Drawing No. 2059524-0501 or No. 2019230-0501 (The Bendix Corporation, Communications
Division), or equivalent. Cooling air need not be restricted to 4.8 cfm during this test because of system losses. Cavity tuned
so as to have a 3 dB bandwidth of 25 MHz centered at 442 MHz.
7/
When used in the AN/FPS-85, this tube shall have a 4,000-hour service-life guarantee. The life of the tube shall be considered
terminated when one of the following conditions exist:
(a) There is an accumulation of 10-anode arcs.
(b) The power output has dropped to the 3 dB level.
8/
This test shall be performed during the initial production and once each succeeding 12-calendar months in which there is
production. A zero defect sampling plan (see 13/) shall be used, with sample of three tubes with an acceptance number of
zero. In the event of failure, the test shall be made as a part of conformance Inspection, part 2, with an acceptance level of 6.5
(see 13/). The regular "12-calendar months" sampling plan shall be reinstated after three consecutive samples have been
accepted.
4
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