JAN VT48 PP Amp Hum noise

JAN VT48 PP  tube low frequency amplifier has some problem to make hum noise on the right channel. Replacement of the tubes proved that the inconvenience is not brought by the tubes but done by some hardware on the right side. Probably, the cause of the noise must be produced by resistor, capacitor or lack of circuit impedance, such as poor soldering method.
The scenery from the bottom shows complicated wiring, but my secret device, oscilloscope will reveal the reason without hard task. Electrolytic capacitor might be the reason, because it is respectable with aging for over 20 years.
12AX7 as an initial stage is relatively easy to obtain, but US Sylvania JAN 48 might be difficult as NIB condition produced over 70 years ago.
Anyway, I'll seek in the Web sites looking for the alternatives in the worsts case.