It's a pity that very high quality capacitors were not available years earlier. That would have eliminated the troublesome mains dropper but would have reduced the income of service engineers. I loved droppers!
As I have mentioned before. The main reason for tube failure was down to the preset LT supply pot. It was rated at 220ohm but would creep up in value to over 2k resulting in a 15v rail before hum instigated a service call. By then it was too late. I used to fit a ceramic high quality pot. Problem solved. John.