At it's lowest setting, this old Speedotron 2401A uses only some of the capacitors. These capacitors are all alike, maybe 12 of them, and they're fully charged at 900volts DC. The duration gets shorter when you disconnect capacitors. This behaviour is typical of traditional channels designed studio flashes. More recent packs have a dial down feature in wich case the voltage is lowered, lenghtening duration, just like your usual monoblock. Still a fantastic, rugged flash system, but you can't stop much action with these systems.