The buzzers won't cause any noticeable lamp dimming unless you buzz every buzzer at the same time. Watch your polarity on the 24VDC. Ground is positive. "A" Battery is -24 VDC Filtered Talk battery. "B" Battery is -24 VDC Unfiltered Signal battery. If you get your talk battery connected to "A" Battery on the Melco, the talk path will be silent.
You have 10V AC buzzers. There are 90 VAC (or ring current) buzzers available. They will have an "ingrown" lump on one of the leads which is a dropping resistor. Those would be connected to RB and RG.
Rcaman
