1. For LM317 I received the output of 11.2V and for LM7915 -10V and for LM7815 at 10.4V
2. I did a mistake with the supply. Next time I won't use SR560 and will use a voltage supply instead.
3. The diode is for protection purpose. How should I use the diode for 7915, should I put it in forward bias or not use it at all?
4. I did check the voltage supply provided by SR560 using a multimeter, they were 12V.
1) Has the DC output voltages of the regulators checked?
2) What's the target voltages of the regulator circuits? And how the voltages were supplied from the power supply port of the SR560? 7815 is the regulator meant for +15V and 7915 is for -15V. So the input voltages need to have at least 3V larger voltages than the target voltages (like +18V for 7815, -18V for 7915). If the +/-12V are naitvely applied, the regulators don't reach the operating point.
Check "Voltage Drop" descriptions in the data sheets of the regulator chips.
3) What's the purpose of these diodes? I believe they are for the regulator protection against the transient sign flip during power switching etc as well as over voltageprotection. The circuit of the 7915 has the larger potential difference (like -18V) while the output has -15V. This means the diode will always be on. If this is just a typo in the figure, it's not a big deal. If this is the real situation, it is a big problem.
4) Why were there such huge 60Hz lines? Was the SR560 properly operated with its battery?