ALBA T324 17″

When the brilliance is advanced the picture
reaches a certain brightness (not very) then begins
to go dark again.
I have had the usual fiddle with the noise
limiter and contrast and manage to get a rather
dark but stable picture. The picture then gets
darker until it is hardly visible an hour or so later.
I have a good meter (Taylor 77A), but 1 am unable to make high voltage tests.
I feel it probably is the brightness control itself,
but I am rather loath to make a move without
expert advice. -E. Williams (Widnes).
This symptom is probably caused by a low
emission tube, the emission of which deteriorates even more as the receiver is left on. However, before contemplating replacement, it would be as well to check the setting of the ion trap magnet on the tube neck (adjust for maximum
picture brightness) and the emission of the EHT
rectifier.