You definately have a short... can be a bugger to track down anmd mjany fuses can be lost trying to find it.
I use a 15A trip switch from Jaycar for this sort of thing... each time it shorts you just push the button.

If some of the lamps are brighter, then this is ,your best clue... trace the power line to these through until you find the fault. 15A is for the headbox only... you should only need to look here unless something is across thre Jones plugs.  Make sure you dont have a loose staple etc

Williams EM games have one major flaw in their design and this maybe worth checking out.

When you lift up the PF the loom of wire rubs against the transformer housing... when PF is down its also on the transformer housing. This wears away the cotton insulation over time and it only takes one tiny bit to wear and touch something and you have a very hard to find short