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AUDIO FORUMS >> TROUBLESHOOTING >> Left channel hum on SE84UFO25
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Message started by Stefan on 08/11/25 at 00:01:24

Title: Left channel hum on SE84UFO25
Post by Stefan on 08/11/25 at 00:01:24

I got a hum on the left channel without changing anything on the system. Here what I tried:
- swapped all tubes that are in there 2 times from left to right, no change, hum still on the left side
- swapped all single tubes with different tubes, no change
- disconnected inputs, no change
- swapped speaker cables from left to right and right to left, hum then moved to the right.

The only thing I notice is that the left mA meter shows 4 bars above 20 whereas the right one is 3 bars above 20.

Anything else I can try or does it need to be sent in to Decware?

Thanks,
Stefan

Title: Re: Left channel hum on SE84UFO25
Post by CAJames on 08/11/25 at 00:29:48

Edited:

If you had blown a fuse under the rectifier one of the VR tubes would be out and you would get zero on the meter so that isn't what is going on.

Have you put in all new tubes at the same time? It is a long shot, but before you call Decware I'd try all new tubes, vs. swapping or replacing in batches.

Title: Re: Left channel hum on SE84UFO25
Post by Stefan on 08/11/25 at 03:42:57

Thanks,
yes, I tried to swap / replace the tubes one set at a time to see find out which ones are the bad ones, but no luck.

And it plays music fine out of both channels, just there is this hum on one channel.

Stefan

Title: Re: Left channel hum on SE84UFO25
Post by CAJames on 08/11/25 at 04:00:32

Quote:

Posted by: Stefan Posted on: Today at 19:42:57

yes, I tried to swap / replace the tubes one set at a time to see find out which ones are the bad ones, but no luck.

I understand trying to find the bad one, but it is possible there is an interaction between more than one tube. It is unlikely, but replacing all the tubes may fix the hum, and is probably something Steve would ask you to do before you send the amp in anyway. If it does fix it then you can start adding the old tubes back to see which ones are good and which ones cause the problem. And much easier than sending the amp to Decware.

Title: Re: Left channel hum on SE84UFO25
Post by Stefan on 08/11/25 at 15:28:01

Thanks, easy enough to do, I'll try that out and report back.

Title: Re: Left channel hum on SE84UFO25
Post by Stefan on 08/12/25 at 04:08:24

Nope, changing all the tubes against completely different ones didn’t change anything, any other ideas what else to try?

Thanks,
Stefan

Title: Re: Left channel hum on SE84UFO25
Post by CAJames on 08/12/25 at 14:43:57

I'm out of ideas, probably time to talk to Steve. Good luck and let us know what happens.

Title: Re: Left channel hum on SE84UFO25
Post by Donnie on 08/12/25 at 16:56:11

Are you 100% certain that it isn't your source?

Does the hum move if you reverse your input cables?

Just thinking....

Title: Re: Left channel hum on SE84UFO25
Post by Donnie on 08/12/25 at 17:04:25

I'll also add looking at your speaker cables. Change them side to side to make sure that the hum stays on the same side.

Also change the power to another socket. Make sure that your source is plugged into the same circuit.

Title: Re: Left channel hum on SE84UFO25
Post by Stefan on 08/13/25 at 05:09:01

Thanks Donnie,
But yes, even no input RCA plugged in I get the hum, replaced speaker cable and power cable, nothing helped.

Guess I go to ask Steve next.

Thanks guys for helping troubleshoot!

Stefan