[Boatanchors] Q of electrolytic capacitors

[Brian Clarke]

Yes, John,

Great photo. But you can't tell from the photo whether that was due to leakage resistance 
or high ESR. In a Pi filter on a mains PSU, it's usually the cap just after the rectifier that 
goes because it is carrying twice-mains frequency ripple current. And, it's usually the 
growing ESR times ripple current squared that leads to accelerated drying out, reduced 
capacitance and then the second filter cap going. 

And why the high ripple current? Because the loudspeakers we had were rather poor in 
the LF region and so we under-filtered the rectified mains; as soon as a load was applied, 
the ripple current grew. A typical CR product in those early days was about 0.02. 
Nowadays, we tend to go for 0.15 to 0.3. Sure, we get a higher start-up charging current, 
but the ripple current is much less.

73 de Brian, VK2GCE.