It appears to me that the 9v battery replaces a resistor and capacitor on the upper triode of the mu-follower driver. If that is the case, these voltages look good and the circuit is operating properly. Some of the solder joints to the ground buss look marginal; I remember having a heck if a time getting those hot enough back in the day! Your hum might be just a failing solder joint to the buss. Poking things with a chopstick while listening might help.
Still, the power supply is always a candidate for hum. It's harder to see it; there are two chokes and three capacitors but the initial 100uF seems to be bypassed by one of the 22uF films - and then I get lost. There's a muddle of components near the film caps which I can't figure out. The perf board over the power transformer appears to be a reverse-recovery spike filter, which solves a potential buzz problem but has little to do with hum.
From the power transformer label, this amp seems to be wired for 100v power, as used in Japan., with a replacement power transformer.
By the way, NIMH batteries lose their charge fairly fast - 10% loss per month, I think. It's not carrying any current in this design, but you'll still want to charge them up every few months.
