TU-8500 Barely audible sound

Hi.
I can barely hear sound if I connect the newly assembled TU-8500 tube preamp to the power amp.
Actually, when I was done with soldering and tested the preamp for the first time, volume was okay but the sound was coming out of the left speaker only. So, I had to desolder some of the joints using soldering wick and resolder over again. Since then this issue started to occur.
Please help me to troubleshoot this issue.

Thanks in advance.
Henry