[Dave Moll]

A bell 1A is just that - a bell and nothing more. Some vendors create confusion by referring to it as a bellset 1A, though the latter refers to a unit containing other components (and, confusingly, not necessarily a bell.

The 150 does indeed need a bellset such as bellset 1 (without an "A"), which contains an induction coil (and a capacitor). The former is necessary for correct wiring of the 150.

You do not say how you wired your 150, but I'm puzzled how you managed to get through to the emergency number (999), which you imply with your mention of "fire, amulance or ...". It is more likely that you achieved something like 112, which is one of the non-emergency services (probably owing to the "2" and "3" each missing a pulse by the dial speed being out).

It is possible to wire a 150 with the transmitter and receiver (and dial contacts) simply in series across the line and get some sort of communication, but there will be a mismatch of impedance (hence the faintness of the sound) and a DC line current through the receiver - for which it is not designed.

As a matter of interest, how did you connect the bell? It should work if you connect it between terminals 3 and 5 of a master socket or equivalent (usually the white and blue wires of a standard BT line cord). Owing to its bell impedance of 1K, it may load the line to the extent of preventing other ringers from operating - often circumvented by connecting a 3K3 resistor in series with the 1K bell. It does, however, require a series capacitor, as provided by the master socket between terminals 2 and 3.