Life Test; Focus Test - B+K precision 467 Instruction Manual

LIFE TEST
It can generally be assumed that picture tubes showing high emission levels
(1.0mA and over) will continue to perform acceptably for long periods of time, and
that the performance will not be degraded appreciably by abnormal supply voltage
conditions such as low heater voltage. However, when the picture tube shows
emission levels that are relatively low (below 1mA) even though they may be in the
GOOD region, it is highly desirable to evaluate performance both from the
standpoint of future life expectancy and behavior at reduced heater voltage. This is
particularly true with regard to tracking performance, and has become an
increasingly important test in these energy-crisis times of "brown-outs" with
reduced line voltage levels to homes.
One of the best means of estimating the remaining useful life of a picture tube is
to observe the decrease in emission with reduced heater voltage. If the performance,
(either emission or tracking) becomes unsatisfactory with a 15% reduction in heater
voltage, you can be assured that the future useful life of the tube is rather limited.
To facilitate this analysis in the Model 467, a LIFE test pushbutton is provided
which automatically reduces the heater voltage by 15% from any normal value
previously set on the heater voltage meter. Simply depressing the LIFE test
pushbutton permits very rapid evaluation of both the remaining life expectancy of
a picture tube and its performance at reduced heater voltage.
Other clues for judging life expectancy are the "warm-up" and "cool-off'
behavior of the cathode. These tests are easily performed by applying or removing
heater voltage while observing emission. Therefore, those sections of the RESTORE
pushbutton switches that interrupt the heater supply are arranged to be operative in
the TEST position.
FOCUS TEST
When the FOCUS TEST pushbutton is pressed, a large resistance is connected in
series with the G2 electrodes (Fig. 4). The focus electrode(s) however, are
connected directly to the full G2 supply voltage through a sensitive neon lamp. The
large resistor reduces the G2 electrode voltage thus allowing more current to be
picked up by the focus electrode which is indicated by the neon lamp glow.
There will always be some drop in emission when the focus test button is
pressed. Some gun structures will exhibit a large drop and others only a very small
drop. Those guns showing a large drop have a common focus electrode that is
virtually a one piece mechanical structure so that an open connection to a single
focus electrode is practically impossible. However, some gun structures exhibiting a *
small drop may employ separate focus electrodes which are interconnected by a
welded metal strap, and an open connection may occur to only one or two focus
electrodes. Even if the base pin has continuity to only one focus electrode, the test
will still show FOCUS-OK. However, an open focus interconnection to one gun will
show a large drop in emission instead of a small drop, thus making it possible to
detect the open interconnection.
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