Hi,
I’ve attached a wiring pictorial for you to peruse. The diagram may not match the wiring of your Pristines so I would suggest you contact the factory to obtain the correct one for your speakers.
It would help if you posted a few pictures of your backplates to give us a better idea of what your describing.
I’m unclear as to what you mean by “bias taps”. The bias level is set via a variable resistor. To set proper bias the shaft on the resistor is rotated clockwise to increase the bias to the point where the panel starts to crackle and then backed off to the point where the crackling just ceases.
A number of people have replaced the brilliance control with a fixed value resistor by setting the brilliance to a level that gives a proper high frequency balance, measuring the resistors value and then replacing the control with the measured fixed value. I would use a 50W non inductive style resistor.
Good Luck with your restoration, I hope the panels themselves are functional and in proper order.
John
