Good Morning Late Wednesday Birds.
ChatterBank5 mins ago
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For more on marking an answer as the "Best Answer", please visit our FAQ.firstly, this is not the symptom of a faulty tube. It is either bad soldering to the heaters, a broken pcb trace on the heater feed from the line transformer, lack of High voltage, (is there static on the screen and the typical "whistle" when on?), a video blanking problem....could be one of various things.
Take the set to a tech for a proper estimate so you'll be able to make an informed repair decision based on actual facts and not based on internet guesses and speculation. Don't spend on repairs more than about 1/3 of the cost of a new set of similar quality or features. good luck!