KEL84 hum when source plugged in?

[Audiophill]

Hi Evereone, new member here, II have a diy kel84 already made that i purchased that works well and is silent untol a source is plugged in then i get a low hum that gets louder as volume incrrases, dosent matter if its a cd, phono stage or rca to jack to plug my phone in to stream? ook a chance on a tube amp of ebay that was very cheap as it looked like a kel84 but in a granite plinth? When it arrived ( it weighed a ton becawhen i got it I use the top was granite on a thick welded steel chassis) I flipped her over and it was a kel84! but they had used the kel84 transformers but not the circuit board! There made it with 2 separate point to point boards, one for each channel, quite messy but quality components used. Can anyone offer any help please?
Many thanks Phill