I have used the blue box before without problems.
I think what might be happening, is the box has a bad ground connection and putting maximum voltage out to the field windings (not regulating.)

More specific, with a bad ground the box voltage reference thinks the voltage is less than what it actually is, so it allows more power to the alternator trying to increase the output voltage (which it does), but the bad ground prevents the box from seeing this increased voltage.

The later style regulator for the dual connection field regulates through the ground path, opposed to the power path like the older style/blue box does. So if the later style box had a bad ground connection the box may try to increase the alternator field current, but the bad ground prevents the current from flowing, so you get a no-charge condition as opposed to an over-charge condition like you are seeing with the older style regulator.

I often run a 16AWG or larger ground wire from the regulator case to the engine block to make sure this dosen't happen. use one of the star washers between the regularor case and wire lug/bolt so the washer cuts through the paint and makes a good contact.

The same type of ground wire works good for the ignition boxes too.