1930? General Electric T-12

[Reece]

The general rule is keep the cap next to the rectifier the same value as original, but you can increase the second cap farthest from the rectifier a bit. Yes, C18 can be 10 or 15 mfd. Check the high voltage before and after the change from the 2 mfd. as too big a C18 can raise the voltage. 10 mfd. should do it IF the source of hum is the B+ supply. You could also have a buzzy power transformer with loose laminations? Or is the hum definitely from the speaker.