How The Model 467 Works; Emission Test; Tracking Test; Leakage Test - B+K precision 467 Instruction Manual

HOW THE MODEL 467 WORKS
EMISSION TEST
The multiplex test method (Patent Applied For) employed in the DYNASCAN
Model 467 tests the three guns in a rapid-fire sequence, on a 1/3 duty cycle
time-share basis (Fig. 1). Each gun is pulsed 20 times per second and the peak
current of each gun is continuously indicated on its individual meter. The current
indicated is "true" beam current - that is, only the current passing through the G1
aperture. A GOOD emission indication on the meter, therefore, assures that (given
the high voltage), the gun is capable of producing adequate highlight brightness on
the face of the picture tube.
The G2 voltage is supplied by a digitally programmed regulator so that it can be
automatically adjusted to the G2 cutoff value of each gun, during the gun's test
interval. This is why the test set-up and procedure is the same for even those tubes
that have a common connection to all three G2 elements.
TRACKING TEST
The multiplex system greatly simplifies the tracking test (Fig. 2). The 1 Vi to 1
limit for emission between the highest and lowest guns is checked by showing this
ratio on the meter scale as a yellow wedge extending upward from the GOOD-BAD
limit line. The TRACKING control changes all three meter readings by the same
percentage so that if all three pointers can be placed in the yellow area, you know
the guns are tracking. Changing the three meter readings by exactly the same
percentage is accomplished electronically by changing the duration of each test
interval exactly the same amount. Thus, if each gun is on for only 1/6 instead of
1/3 of the time, each meter reads 50% of its former value.
LEAKAGE TEST
The multiplex system simplifies the leakage test (Fig. 3). Like the limit used to
make a GOOD-BAD judgement of emission, a leakage limit somewhat higher than
the manufacturer's limit for a new tube is used - a limit at which you might expect
trouble to begin showing up in a typical TV set. Fortunately, such a leakage limit is
just high enough to cause a neon lamp to glow. By using a group of 5 lamps (one
for each cathode, one for the heater, and one for Gl), and multiplexing the test
circuit, we can observe leakage between any two cathodes or from any cathode to
the heater or Gl. (Both lamps will glow, showing which two elements are involved.)
This test is made automatically with the function switch in the SET-UP position
and requires no operator adjustment. It will detect almost any leakage problems
that do occur, including those troublesome cathode-to-cathode leaks.