That's right, no access to the 12V module supply, pity. So the power for the bell is always missing. There is a relay on board, but it just closes the circuit available where it says "24v/1A max." when the phone rings. I guess either a bell or a horn will need much more than 200 mA.

True, the 5.5/2.5 DC power connector failed to contact at my first trial, and I had to turn round to get the power through and light up the red diode pilot. It can be a sort of if it disconnects after mounting because I am going to place it not far from the ceiling.

I haven't find the jumper yet, but it rings longer than the ringing sound on the earphone.

 

If you got the 5.5mm/2.5mm connector, you got the wrong one. Only if you got the 300 mA recommended supply do you have 200 mA to play with at 12 V. So, what I am saying, is that you could get a 12 V, 1 Amp supply and have 900 mA to play with. The ratings of the barrel connectors vary, but 1 A seems common,

 

Sorry, I can't get the stuff now, but on a few days.