An hour ago I looked at an eight flag manual reset panel, made by Peerless, unmarked as to voltage but set up for direct current. It is undated, but is wired with varnished copper and cotton clad copper, and the case is straight-sawn white oak. I would guess it to be 1890-1900.
There is a bus bar to which the (-) terminals of the flags are attached, the bus bar is attached to the (+) lead of the gong, and the (-) lead of the gong goes to the (-) lead of the cell.
The (+) lead of the cell attaches to a bus bar, which has eight thumb screws (one for each call button. The buttons are all missing, but I assume that they would then hook to the thumbscrews on the (+) side of each solenoid. When the circuit is complete, it would charge that particular solenoid, and the bell, being in series past the common bus bar, would ring.
The hand-operated reset would tip the flags back to the up position.
Earlier today I scrounged out a Partial panel, unmarked and obviously missing parts. Instead of old-style solenoids, the panel has individual relays with an oscillating "actuator." The actuators, one for each number, have a ratchet wheel of 12 on the arbor, and an indexing pawl to keep it going one way. There is a disc sharing the arbor with each ratchet wheel with alternating low and high points, and a long-leggety "feeler" attached to a set of button contacts riding the high and low portions. When the feeler is on a high portion the switch closes and energizes a separate relay, which presumably administered a signal. Activate the relay again and the ratchet wheel will step ahead one tooth and the feeler will drop into a low portion and stop the signal. It also has three relays on slate bases. The relays are marked 12v ac, so I am guessing this thing had a transformer but no rectifier.
Of the extra relays, two are normally open, single pole, one is double pole, double throw. One of these is the signal relay. One is marked "call for heat" The double-throw is unmarked, but has a small transformer whose primary leads are in series from the normally open contact of the secondary. I almost wonder if this drove a speaker someplace for an intercom.
Aside from this too much is gone off of this panel to tell any more of consequence about it.