MX110 Loud Hum

[Bitty]

I was wondering if anyone would know what this might be. Out of the blue listening to radio I started to hear a loud hum. I disconnected all components its still there. I swapped out all the front tubes even the ones in the back corner still there ( did not mess with radio ones). I tried different cables still there. I tried my amp with a device on it's own and that works fine on its own. This hum is on every input its constant loudness for the most part. I can turn it all the way down it's gone. But just a smidgen up it's loud and doesn't really get louder kind of does not sure then dips down a little then comes back up. If I try to stay in that dip though it creeps back up. Still that is still to loud there as well. Its kind of a lower hum not super low, but lower. I switched directions of the plug as well. My amp is plugged into it, and thats how I tested the amp with the volume all the way down on the preamp.

 

[quartersaw]

I was wondering if anyone would know what this might be. Out of the blue listening to radio I started to hear a loud hum. I disconnected all components its still there. I swapped out all the front tubes even the ones in the back corner still there ( did not mess with radio ones). I tried different cables still there. I tried my amp with a device on it's own and that works fine on its own. This hum is on every input its constant loudness for the most part. I can turn it all the way down it's gone. But just a smidgen up it's loud and doesn't really get louder kind of does not sure then dips down a little then comes back up. If I try to stay in that dip though it creeps back up. Still that is still to loud there as well. Its kind of a lower hum not super low, but lower. I switched directions of the plug as well. My amp is plugged into it, and thats how I tested the amp with the volume all the way down on the preamp.

Check the contacts on the rotary switch underneath the amp

 

[dshoaf]

If you've got a Z series and the problem is on both channels equally, then you're dealing with a power supply problem most likely. There are only 2 tubes in the preamp section that are common to both channels: 6D10 and the single 12AX7. Rock those 2 tubes and see if there's a bunch of noise generated. If one tube, replace it. If both tubes, thump both of them with your finger and see if you see some sparks. Swap any tube that acts out.

Otherwise, I'd suggest it not be used until it has been looked at - its down in the power supply. Has this unit been restored or rebuilt?

Cheers,

David

 

[Bitty]

Yeah its been gone over ( year maybe two years ago) except the tuner. Had caps replaced i'm sure. I thumped both tubes steady sound no weird noises. Rocked them a little nothing added as well just that steady hum. I will have to see what that rotary switch is.

 

[Thocom]

Id look under the hood to see if anything looks obviously blown, or a bulging cap, etc..
Remember, there's a high voltages in there, even after it's been unplugged.

 

[Thocom]

Here's what mine looks like.