[Dave Moll]

As others have said, more information is needed to be certain, but it sounds as though your old telephone have been converted to use an external ringer capacitor, but you are making two-wire connections from your Panasonic 206 (albeit not a PABX with which I am familiar).

If this is the case and your telephones are terminated with a standard BT plug, what you need is to have the extension lines from the 206 going to master sockets (which contain ringing capacitors), not extension sockets. Alternatively, as Paul says, plugging a BT-style ADSL filter into each extension socket should have the same effect.

The reason that your "cheap Chinese 'phones" will work in this situation is that they will have their own ringing capacitor.