JVM215C Squeal/Bias - my.marshall.com

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JVM215C Squeal/Bias

I have a JVM215C and the other day I was experiencing some issues. I thought it might be power tube related so I re-seated the power tubes but that did not help and the amp was still making a high-pitched squeal. The squeal would come and go but other last 3 days, it was pretty consistanct. I also noticed that the amp at times would go from a muddy-low powered sound to a more clean, high powered sound. I then removed the head from the combo so I could test the bias of the tubes. For one side, I get 33 but for the other, it will not register. The amp has not made the squealing sound today so I wondering if maybe the tube for that one socket is dead (although it appears to have power to it -- and its not white). Can someone let me know if a faulty power tube could make one side of the bias terminals not register?

thanks!

joe...

Tubes

asked 16 Dec 2019 at 05:46 PM

Answers: 2

Hello Joe,

We would recommend that you have the amplifier looked at by an engineer to see what is causing the fault.

Kind Regards

Marshall Support

answered 17 Dec 2019 at 08:22 AM

My amp is from 2017.. would it be still under warranty. I am not original owner. - 17 Dec 2019 at 12:39 PM

Hi Joe,

If you contact your dealer they will be able to confirm this for you.

Marshall Support - 17 Dec 2019 at 02:05 PM

I had some other EL34 tubes laying around so I installed them and biased each at 40 and so far, all looks good so I'm hoping it was just a bad power tube. - 17 Dec 2019 at 04:02 PM

After replacing the power tubes, my issues were resolved. Both terminal of the bias block began to work and the squealing went away.

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asked 16 Dec 2019 at 05:46 PM

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answered 17 Dec 2019 at 08:22 AM

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edited 20 Dec 2019 at 02:14 PM

answered 20 Dec 2019 at 02:14 PM