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1100 man · 29th Aug 2017, 9:23 pm

Hi Lawrence,
I presume the current needed to recharge the capacitors during the positive half cycle will be at least as much as the HT current. This will effectively double the current through the dropper and the heat generated will increase by a factor of four (I squared * R). So in the case of this set, without considering the ripple current, dissipation =5Watt. Factor in the ripple and the dissipation goes up to 20W!! Well, I'd never thought about that before- that might explain why in old TV's it seems to be the HT section of the dropper that has failed rather than the heater section.
Theoretically then, if we were to use a bridge to full wave rectify the HT supply, the ripple current would be greatly reduced. That would imply that the series dropper would need to dissipate less power. Is that true?
Many thanks for your help.
Cheers
Nick

29th Aug 2017, 9:23 pm	#100
1100 man Octode Join Date: Apr 2016 Location: Ventnor, Isle of Wight, & Great Dunmow, Essex, UK. Posts: 1,377	Re: Pilot PT650 "Spacemaker" Television Hi Lawrence, I presume the current needed to recharge the capacitors during the positive half cycle will be at least as much as the HT current. This will effectively double the current through the dropper and the heat generated will increase by a factor of four (I squared * R). So in the case of this set, without considering the ripple current, dissipation =5Watt. Factor in the ripple and the dissipation goes up to 20W!! Well, I'd never thought about that before- that might explain why in old TV's it seems to be the HT section of the dropper that has failed rather than the heater section. Theoretically then, if we were to use a bridge to full wave rectify the HT supply, the ripple current would be greatly reduced. That would imply that the series dropper would need to dissipate less power. Is that true? Many thanks for your help. Cheers Nick