Mesa Boogie Alien Buzzing

[CEHMusic]

Hi All! New to this block here.

I have an older Mesa Boogie RectoVerb 50 and it has worked great for over a year (purchased second hand from craiglist).

Recently, I've noticed some electrical whirring in my amp, but with so many things plugged in my room, I assumed some grounding that I can handle later. After it seeming to get worse, I tested in more environments seeing it was not my room.

I had a feeling my pedalboard was causing this whining/electrical/buzzing noises, however upon further trial, with nothing else plugged in, I believe it is coming from the amp. Potentially a grounding issue?

Might anyone have any input as to what may be causing this?
I am wanting to take to a Mesa Boogie Repair certified place, however closest location won't be available until January. Any thoughts as to what may be causing this before I can take it in physically?

Any input would be fantastic! Thank you!

Here is a video I uploaded showing whats going on (1:07) - hope the links works
https://youtu.be/btpmktvHHiw

[Jon Snell]

That sounds like an anode load resistor breaking down to me. Either 100 or 220k.
I would replace them with MO 1/2 Watt types.

[Pedro Vecino]

It can have a multitude of origins but one possibility would be that the input jack did not have perfect mechanical contact with the chassis. I have seen that effect on an F30.
That nut must be incredibly tight.

[CEHMusic]

That sounds like an anode load resistor breaking down to me. Either 100 or 220k.
I would replace them with MO 1/2 Watt types.

Thank you Jon! Your sharing has allowed me to research more about these innards of the amp. I will do more research and study up on this.
Much appreciated!

[CEHMusic]

It can have a multitude of origins but one possibility would be that the input jack did not have perfect mechanical contact with the chassis. I have seen that effect on an F30.
That nut must be incredibly tight.

Thank you Pedro! That is another possibility I can see and will certainly look into. I am having some more stuff to look into now and research.
Greatly appreciated!

[Mick Bailey]

Do any of the controls affect the noise? turn everything down to zero - is the noise still present?

Also, is the noise confined to one channel - is it better or worse on the other channels?

[Intripped]

I would also try and move the tubes a little while they're in their sockets, in order to clean contacts.

[CEHMusic]

Do any of the controls affect the noise? turn everything down to zero - is the noise still present?

Also, is the noise confined to one channel - is it better or worse on the other channels?

Apologies on my delay! Crazy week with the holidays. Thank you for your input.

I have just tested, and on both channels, when I heard the issue you hear, I turn all knobs off two 0 and the noise continued.

[CEHMusic]

I would also try and move the tubes a little while they're in their sockets, in order to clean contacts.

Thank you for the input! I have researched changing tubes just so I can take out and reinsert the tubes for the intent to clean the contacts, and the issue continued to persist.

Dang!

[CEHMusic]

I have gone through the video here, and it seems like it may be a pre-amp issue

Start at 9:16
https://www.youtube.com/watch?v=wSl-l9aWDHw

[Mick Bailey]

My thought is that with all controls set to zero the problem lies with the power amp or power supply. My own check would be to remove the Phase inverter tube and see if the problem disappears. This completely removes the preamp from the signal path, just leaving the power tubes and power supply noise (if any). Here's the tube layout that I think should match your amp; https://www.eurotubes.com/store/pc/M...ption-p457.htm

[CEHMusic]

My thought is that with all controls set to zero the problem lies with the power amp or power supply. My own check would be to remove the Phase inverter tube and see if the problem disappears. This completely removes the preamp from the signal path, just leaving the power tubes and power supply noise (if any). Here's the tube layout that I think should match your amp; https://www.eurotubes.com/store/pc/M...ption-p457.htm

This was a great diagram! I learned so much here in this process.

I have done a handsome amount of troubleshooting now, and it seems like the issue might lie in the pre-amp 6L6 GC STR 440 Power Tubes specifically.

When removing V5 from my amp chain, the issue persists (confirming buzzing coming from speaker). This should rule out V1-V5 and moves to the power tubes.

I removed one at a time the 6L6 and the issue did not show up again. While I cannot tell specifically which of the 6L6 might be an issue, one seems to rattle a bit more than the other.

While not ideal, I may just buy both 6L6 tubes to see if it fully goes away.

Any thoughts there?

[Mick Bailey]

It could be just an oxidised 6L6 socket or tube pins and reseating the tubes has effectively fixed the problem. I would be tempted to see how it goes for the next few days. If you're uncertain about the output tubes it would be a good plan to replace them anyhow.

[CEHMusic]

I have attempted reseating the tubes a few times and it does still continue. I do believe that replacing them is ideal at this point.

The tubes I have currently are Mesa Boogie 6L6 GC STR440. These have been crazy difficult to come by, if at all. I really only have had real visibility on eBay for these.

Would there be any issues in using Mesa Boogie 6L6 GC STR44X? Just a different ending number on the 6L6 power tubes. I've seen a handful of other and am wondering how crucial the 440 would be.

[Mick Bailey]

A 6l6GC is a standard tube available from a range of manufacturers. Mesa's designation is based on who actually makes the tubes (Mesa doesn't make its own) and is their re-branding for Shuguang, Sovtek, JJ and other tubes. Mesa amps do not have any means to adjust the bias and their tubes are graded within a range that will work in their amps without running too hot or cold. There are some suppliers that supply OEM branded tubes that fall within Mesa's range and are specifically intended for use in Mesa amps and these are much cheaper.

The STR-440 type is not critical at all, it just specifies one particular manufacturer. Any Mesa 6L6GC will work. Where do you live?