MIL-PRF-1/779K
NOTES:
1. This value is for operation under fixed-bias conditions. With cathode bias, Rg/g may be 1.0 megohm maximum.
2.
Pp/p on one section may be as great as 4.2 watts maximum providing that the total for both sections does not exceed 7.5
watts.
3.
See "Reduced pressure (altitude) rating", and altitude, maximum peak voltage.
4.
Test each section separately.
5.
This test shall be performed at the conclusion of the holding period.
6.
Tie 1k to 2k; 1g to 2g; and 1a to 2a.
7.
Operate heaters in parallel.
8.
Prior to this test, tubes shall be preheated a minimum of 5 minutes with all sections operating at the conditions specified
below. Test at specified conditions within 3 seconds after preheating. The 3-minute test shall not be permitted. Grid
emission shall be the last test performed on the sample selected for the grid-emission test.
Ef
Eb
Ec1
Rk/k
Rg/g
Meg Ω
V
V dc
V dc
Ohms
14.0
120
-2
0
1.0
9.
The positive portion of the grid pulse shall be a square wave meeting pulse shape requirement of method 1296 and, in
addition, the maximum amplitude shall occur within the first 20 percent of tp. The pulse shall be applied to the grid by
means of a driving circuit which produces the specified peak pulse voltage directly at the grid terminal with respect to
cathode. Grid resistance, not exceeding 50 ohms may be inserted to prevent oscillation, provided readjustment of grid
drive is made to maintain the specified pulse amplitude directly at the grid terminal. Peak currents shall be measured by
means of a high impedance oscilloscope, or equivalent device, connected across a cathode resistor of 1.0 ± 0.1 ohm. The
specified limit refers to the maximum of pulse amplitude.
10.
Test each unit separately with test voltages applied to opposite section. Tie grids to negative end of individual Rk through
individual 100-ohm resistors. Adjust individual Rk for specified forward anode current ± 5 percent as measured on the
forward half cycles of anode voltage. After a minimum of 5 minutes operation as above, measure reverse anode current on
the reverse half cycles of anode voltage. See figure 2.
11.
Acceptance sampling procedure shall be in accordance with "Base-strain test, miniature, sampling ( method 1121)', except
that data covered in "Acceptance and rejection criteria" shall be modified as follows:
(a)
Accepted if no defects for class "A", "B", or "C", respectively (see method 1121), or if no defectives are found in the
sample.
(b)
Rejected if any defectives for class "A", "B", or "C", respectively, or if any defectives are found in the sample.
A grid resistor of 0.1 MegΩ shall be added.
12.
13.
This test shall be conducted on the initial lot and thereafter on a lot approximately every 12 months. When one lot has
passed, the 12-month rule shall apply. In the event of lot failure, the lot shall be rejected and the succeeding lots shall be
subjected to this test until a lot passes.
14.
Envelope temperature (TE) requirements, when measured in accordance with the temperature by conduction-band
measurement (method 1226), will be satisfied if a tube having bogey Ib (±5 percent) under normal test conditions, is
determined to operate at or above minimum specified temperature at any position in the life-test rack.
15.
The positive portion of the grid pulse shall be a rectangular wave meeting pulse shape requirement of method 1296. The
pulse shall be applied to the grid by means of a driving circuit which produces the specified peak pulse voltage directly at
the grid terminal with respect to the cathode. Grid resistance not exceeding 50 ohms may be inserted to prevent
oscillation, provided readjustment of grid drive is made to maintain the specified pulse amplitude directly at the grid
terminal. The pulse width, tp, shall be 10 ±2 µs, and the duty factor, 0.9 percent to 1.1 percent. Self-excited life-test
circuitry is permissible, provided any additional anode voltage drops during the time of the pulse are compensated for by
increasing Ebb. No fixed Ec1 need be applied under self-excited conditions.
16.
This specification sheet utilizes accept on zero defect sampling plan in accordance with MIL-PRF-1, table III.
17.
The life-test sample shall consist of the lesser of 20 tubes or 10 percent of lot size and no tube failures shall be permitted.
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