Generally, this is indeed a funky solder joint.
What I would do is to plug a cheap pair of headphones into the Crack, plug the power cord into the Crack (but not the wall), then get it situated in the base so that the guts are facing up.
Plug the power cord in to get it running, then put your cheap headphone on.
With a wood chopstick (NOT A PENCIL!!!), gently poke around each tube socket pin, and each component. There will come a time when you poke something with the chopstick, and you get some crackling out of your headphones. This will direct you as to where you need to be soldering.