Zero Crossing Circuit

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Original poster: "Barton B. Anderson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla123-at-pacbell-dot-net>

Hi - whoever posted the schematic at the following url: 
<http://www.macinhouse-dot-com/tesla/stsg_zc_driver.gif>http://www.macinhouse.c
om/tesla/stsg_zc_driver.gif 

My humble appologies. I was going through mail, brought up the schematic,
deleted the email, then looked at the schematic and wanted to reply. Sorry
about that. 

Can you verify the following for me? (I'm curious if I'm getting the circuit): 

It looks like the zero-crossing is taking place at Q1 and Q2. These transistors
are used to drive the input of pin 2 of the 555 at zero-crossing. (Couldn't a
comparitor be used here to replace Q1, Q2, and the 555?). Anyway, the detected
zero crossing input is clocking the 555 output, of which is driving the base of
Q3, whose 50k pot is adjusting the voltage ratio for the base of Q3. 

It appears this is a circuit where a delay is used (variable R6, R8, and C3 for
when Q3 turns on) which defines when Q4 dumps the voltage across C4 and R10
through the primary of the HEI. 

I guess this is what I'm getting at. 
Is this circuit detecting zero-crossing, then delaying "from zero" when the gap
will fire? 

Thanks for any help with this 
(I'm not the greatest at circuit theory), 
-- 
Barton B. Anderson 
<http://www.classictesla-dot-com>http://www.classictesla-dot-com