Power transformer is ok if tubes light and it doesn't overheat. Unlike other parts they don't get weak.
Check the switch on the unit where tubes don't light. Check continuity of the power transformer with an ohm meter.
Important to replace electrolytic filter capacitors. They dry out over time, lose capacity and allow hum. In some cases these caps short and will destroy a power transformer.
May need to replace the crystal critridge? They go bad over time especially with temperature changes. If the amplifier is operating touching wires going to the cartridge will cause hum.
Norm
:I have two V-M phonos that I would like to get working. Different models, same amplifier. I think the power transformer in each is dead or dying, but I'm not sure. In one, the tubes won' light up in the chassis, but they all light up and check out within specs on my Mercury Tester. The other lights up, produces normal low db 60 Hz hum, but barely any sound when turned up all the way. Paper capacitors have been changed, resistors all within tolerance, did NOT change eletrolytic filter. V-M Audio Enthusiasts doesn't have the transformer, Antique Electronic Supply refuses to give technical advice of any kind to help me figure out which of their transformers to buy (burns me up--they used to!!!). I know just enough about tube technology to be dangerous--I don't know how to figure out things like what each capacitor or resistor does or why it does what it does. Advice, anyone?