symetrical power supply 100w +-12v for a 50 years old amp

[e3k]

hi a friend of mine build an amp 50y ago and now he is getting humming noises after a while of usage. he measured the power supply and got 10v on one and 12v on the other branch.

initially he wanted to buy a new amp for 50E but i told him to repair the old stuff. probably a caps job would do.

starting this thread as an invite for my friend eventually he will register and join us.

check the photos.

now the question is what could be causing the humming sound?

 

[JMFahey]

Both branches/rails "should" have same voltage, so this 20% difference can indicate capacitance in the lower one way lower than normal, probably dry electrolytic.
I would replace both to begin with.
Scoping rails should show lots of ripple on the weak one.