Low hum from amp

Is this a balanced amp?..are you using single ended?

Thanks jea48

Appreciate the feedback.
Yes, checking tubes tomorrow.

@ greh OP

If you had said the hum sounded like 120Hz then that would indicate an electrolytic filter cap/s in the DC power supply.

60Hz..... My first thought would be a ground loop hum, except where you said the hum doesn’t start until after 30 minutes after powering up and listening to the amp.
To me a ground loop could care less how long the amp is powered up.

I would suggest you need to first isolate the amp from any front end equipment. Disconnect all ICs from the inputs of the amp. Turn on the amp and listen for the 60Hz hum from power on to after 30 minutes. If no hum the hum is caused by a front end source.

If after 30 minutes the hum starts then it has to be the amp.
You never said the 60Hz hum was only coming from one channel so I assume it is coming from both channels.


I ran across this video that I found interesting. Could the 60Hz hum be caused by a bad small signal tube? Maybe, if the heater/filament voltage is AC.
https://www.youtube.com/watch?v=GrVtX0QGNls   

Jim

.

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.

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

.

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

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

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.

60 hz hum from a deteriorating power supply cap.

Rogue?

When did this start?

"the hum does not get louder but stays at the same pitch."
It stays at the same "amplitude" or level (or volume or loudness) not "pitch".
Pitch is different than loudness.

Ground loop, maybe.

Thanks to all of you for your response-I appreciate it!
Mike, yes it's coming from both the amp and the speakers but it's definitely starting with the amp.
Thanks again!

per noromance, more often than not it's transformer hum caused by the transformer coming loose with time--you can try screwing it back down tight, but make sure you leave unplugged for a couple of days before you try it

If it's coming from the amp -- the physical amp cabinet -- and not the speakers, it may be the power  transformer humming. This occurs when there's a little DC offset on the line (not uncommon). A cure is available as the AVA HumDinger. I have three; they work great.

If not the speakers, probably just transformer hum caused by dirty power or poor mounting of the part. Try another outlet.

From just the amp or the speakers as well?