I finished assembling my second A12 and I'm get +-25V between pin 3 and pins 4&5 on U1. I can't see any problems with the component installation.
I've checked all the caps mentioned that could be potentially installed backwards, looked for shorts etc. but I am not finding any issues. I did a visual check between another A12 that I finished and that is working well and I can't see any differences.
Initially when I first powered up, I blew a cap at c15 that I must have wired backwards. Since replacing it, I re-powered and am now having the issue described. Could it be that I damaged some other components on my first power up?