Low hum from amp

My amp is a Manley Stingray.
When I first power it up, the hum isn't audible until I'm about 30 minutes into listening.
Thank you dweller for the correction.

Did it go from not humming at all to recently humming without you changing up anything?

https://www.psaudio.com/ps_how/how-to-find-and-fix-hum-extended/

greh OP131 posts

03-13-2020
5:42am

My amp is a Manley Stingray.
When I first power it up, the hum isn’t audible until I’m about 30 minutes into listening.

When I first power it up, the hum isn’t audible until I’m about 30 minutes into listening.

That could be caused by a filter cap in the power supply going bad. Does the hum sound like this?
120Hz hum.
https://www.youtube.com/watch?v=pC4Uzt0qm2E

Or does the hum sound like this?
60Hz hum?
https://www.youtube.com/watch?v=SVZ2P0KsLic

.

Thanks again everyone for the feedback.
jea48, thank you for the links.
It's 60Hz
Mind you, I can still listen to music because the hum is that soft, but it's still there.
And of course it's more audible when the amp's powered up but there's no music playing.