Any amp tech here ? Need help

djemass · Aug 5th 2015

I plugged my amp today and this appeared :

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a kind of buzz/harmoniser unwanted effect. This is even more evident at the end of the video. Any clue?

Thank you guys

Michael_dk · Aug 5th 2015

That sucks. Does it hum more than usual?

djemass · Aug 5th 2015

hi

it is not a matter of hum, there are these kind of formants/buzz with seem to harmonize the original note... very strange. This already happened once, and after some profiling and playing during some hours, the problem disppeared... and it is back again

strange

JuLai · Aug 6th 2015

I'm not a amp tech, but I know two guys that got somewhat similar sounding sub-octave or ring modular kinda sound in their Mesas after the amps got warmed up a little. As I recall the problems were somewhere in the filtering side; the mains AC leaked (or affected somehow) to signal AC. Gladly those weren't that expensive to get fixed.

Tilman · Aug 6th 2015

Sounds good !!

Most likely the filter capacitors.
Is the amp old ?
If so, some power supply ripple filter capacitiors might have given up and can cause this kind of problem.

If this is the case, the overall hum level usually increases too.
Bring it to the amp tech and have them exchanged. Be careful if you want to do this yourself. Filter capacitors in tube amps can hold high voltage for quite a while.

Tilman

djemass · Aug 7th 2015

Thank you for your feedback !! This year is definitely NOT a good year for the 2c+... Hopefully the Kemper sounds glorious

DamianGreda · Aug 7th 2015

I think this is because one of the triode tube in a inverter or power stage dies (or some lack of contact).

Since the inverter tubes and power stage are push pull you will have only one half of the signal - thats why the octave effect appear.

Try to replace Power tubes pairs and the inverter triode as well.

Peto · Aug 7th 2015

Hey Dje! Sad to see your amp is seriously sick this year.
I hope it will be fixed soon. And don't forget to profile it's broken sound!

djemass · Aug 8th 2015

Hi Damian,

Thanks for your feedback.
I will make a test with the inverter tube first.
I will replace for the test with a standard Mesa 12ax7 to check if this is that... about the power tubes, they have been checked by a tech very recently and seemed to work perfectly.

I keep you informed

waraba · Aug 9th 2015

It sucks, sorry for you Dje, I hope you got this fixed soon, so we can enjoy new MarkIIC+ profiles.

okstrat · Aug 9th 2015

Filter caps most likely. I'd take it to a trusted tech or ship it to Mesa for service. A tube issue shouldn't do this. If the filter caps finally blow they will leak electrolytics all over the inside of the amp and that will damage the PCBs. I'd stop using the amp and get it to a tech or Mesa immediately. A recap shouldn't be super expensive but if you have a cap blow and damage the amp further it's going to be MUCH more expensive.

Pete

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