Medved, i removed this ballast from 2x40w fixture
And how that was wired?
You mentioned both lamps parallel with no starters. That would suggest a redundant circuit with one lamp working and the second as "stand-by" in an instant start concept. For such system the SOX ballast would be just the required ballast to provide reasonable run current (0.35A; for 0.43A lamp it is still OK), as well as high enough OCV (~600..700Vpeak with the ~3uF) for cold cathode ignition (that would not be a lifetime problem, if the lamps are supposed to run long time for each start).
The redundant circuit (the one with lower striking voltage would ignite, leaving the second one OFF; When the first one fail and so does not ignite, the second lamp take over, so the fixture get more than double the lamp life and way greater reliability) could reasonably work only with 2 terminal discharge lamps connected plain parallel (so cold started). Managing the heating current would make the gear way complex (it would require an active switching element, like relay or so): Connecting them to low voltage heating source would mean the lamp, what is OFF, would be heated, so the cathodes would evaporate, so degrade, so compromise the overall reliability. Filaments connected in series would mean the current path would be lost, when one of the filaments break, so compromise the reliability as well. Connecting complete lamp+starter combos parallel mean the starter's would interfere with each other, causing starting difficulties of the overall system. Moreover if one starter close sooner than the other one, it's lamp would most likely run and after it wear out, that starter would cause the complete setup to flash, giving no chance to the second one to take over, so simply not working as redundant system either.
