Hi teamgardner,
TR1 & 2 In the pod replaced by BC557
I recommend that you change 'BC557' to 'BC557C'. This is the transistor that Phil quoted.
The reason for this is the parameters for the 557 are not the same as a 557C.
The gain (hfe), or the amplification, are not the same. Check the following:
BC557 minimum gain is 125
BC557B " " " 220
BC557C " " " 420
In a worst case scenario you fit a 557 that has the min. gain you could end up with the system not working correctly.
Regards.
KarlG.