you can have two identical system6 williams machines, both with new flipper parts and clean playfield, yet one machine you can make the lock shot, and the other you cant. (Note this problem isn't just on Firepower, but also on say Black Knight with the long left lower-to-upper playfield shot, along with a few other games of this era.)

The problem with system6/7 games and flipper power has to do with the transformer. in 1980 the way they were wound wasn't technically as accurate as today. That is, you get variances in the windings. This proves to be a problem on some games because the output coil voltage can be a volt or two lower than an identical transformer in another game. (Also if your wall voltage is lower than your friends, that will have an influence too, as the coil power is not regulated.)

This is why Bally used 42 volts for coils. it allows for more variance in coil power. Also it allows better adjustment in the coil power themselves. This is also why Williams eventually went to 50 volts for high power coils.

So what's the answer? Well i've tried all sorts of thing. One thing was to have Steve Young (pinball resource) build me some custom flipper coils with my specs. I would say this helped, but not enough to make it worth the while. The problem is since sys6 games are 30 volt coils, there isn't a lot of room in flipper coil modification. The ohms for the high power side of the coil is darn near a dead short as it is, so you can't take the resistance down much more. This is why 42 or 50 volt coil voltage games are a better idea (and one that Williams eventually did, but unfortunately not until late system7/9 and system11 games.) Swapping transformers is another idea, but that's a crap shoot and who has transformers lying around anyway?

The last resort is actually a somewhat simple one. That is to put the game on "high tap", similar to what we do with EM games. It involes re-tapping the original transformer for 100 (Japanese) voltage. The down side of this is now the GI will be "too hot", and you need to turn the 6 volt power down using a 35amp bridge rectifier (wired incorrectly!) This will drop the GI voltage about 1 volt, making up for the higher transformer output. The 12 and +5 and 100 volt circuits will be regulated, so that doesn't need any work. The CPU controlled lamp voltage will end up a bit higher too, but that's OK, as that circuit is somewhat regulated by design.

Anyways, there ya have it.

personally i wouldn't change the set up to 100 volts on an F14. instead i would look for a dedicated 6 volt transformer, or a different transformer.