Philips PM 5508 Operating Manual page 50

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Fig. Vll-26. Vectorscope display of the "COLOUR BAR"-pattern
In some types of colour television receivers (e.g. in the PHILIPS K7-type)
normal cathode resistors have been used for the picture tube instead of VDR
resistors (like in the PHILIPS K6-type)
As opposed to VDR resistors, normal resistors will cause negative feedback
of the colour difference signals to the Wehnelt cylinders. On account of this
the amplitude of these signals should be adapted to the degree of feedback.
For servicing these types of receivers the "COLOUR-BAR" pattern consists
of colour-bars with a white lower-section.
The white lower-section which has the same video amplitude as the white
bar in the upper part, serves as a reference so .that the amplitude ratio of the
colour difference signals can be adjusted while using the picture screen
as an indicator.