AC vs DC charging circuit question

[ghub005-at-xtra.co.nz (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hello list

I've been wondering about something for the last few days. 

In an AC charging circuit it is common for the SG to fire near the 
peak charging voltage (I'm disregarding LTR circuits). What 
happens to the energy carried in the latter half of the charging half-
cycle? I guess that this energy is just dissipated through the 
'shorted' spark gap - but wouldn't that make a fullwave DC charging 
circuit twice as efficient? (i.e. since the charging circuit's energy is 
stored right across the half-cycle)

However, I understand that equivalently powered DC and AC coils 
don't display a large amount of difference in their spark output(?).

Can anyone tell why this is? Of course I'm assuming that the DC 
filter cap is isolated from the tank cap (otherwise it would also just 
discharge through the SG). 

Of course that begs the question of how to actually isolate a DC filter 
cap(s) from the resonance in the tank circuit. I'd be interested to 
know what methods are in use.

Best regards,

Gavin Hubbard