Mark V:35 humming that comes and goes

[kyldh]

Hello,

I just bought a used Mark V:35. It arrived yesterday and I played for about 30 minutes or so without an issue. Eventually though, an annoying "hum" just swelled up out of nowhere. It was about the same volume as my guitar, so I couldn't really use the amp while it was going on. After 15-20 seconds, the humming went away and all the sudden it smelled like something was burning. I checked the EL-84s and they all seemed to have a normal glow. After that, I immediately turned off the amp and just went to bed because I was too tired to troubleshoot. haha.

When I get home today I plan to check it out further but I wanted to double-check and see if that sounded like a typical bad tube, or if there's something else I should check? Maybe one of my 12AX7s got damaged in shipping... it just seems strange that was working just fine for 30 minutes or so before the issue surfaced.

Thanks a lot!

 

[Nicklotsaguitars]

Pre amp valve hum tends to be set back from the main sound. So it could be components causing it, if not a bad valve. They manifest in different ways and noval valves like the El84 are quirky.
Is it doing it in one setting and not another? When you're rested, eh ;-)

best of luck mate

 

[jb's 52]

Last time I had that hum it was from a brand NEW power tube. I'm using the bigger Mark V.
After troubleshooting with my old set, I found that is was one of the two inner power tubes.

 

[kyldh]

It's strange, but so far the hum hasn't come back. So, to summarize, it hummed, then it smelled like something got VERY hot, and now everything is just fine... odd. I ordered a spare set of tubes that I suppose I'll just swap out at the next sign of failure.

With my luck, the issue probably won't resurface until I take the amp to band practice or a show. :lol:

 

[gjohung]

I have similar issue on lower power mode. 10 watt. 35 watt does not hum...

 

[jb's 52]

It's strange, but so far the hum hasn't come back. So, to summarize, it hummed, then it smelled like something got VERY hot, and now everything is just fine... odd. I ordered a spare set of tubes that I suppose I'll just swap out at the next sign of failure.

With my luck, the issue probably won't resurface until I take the amp to band practice or a show. :lol:

You probably want to swap out the bad tube before a failure. It's what Boogie recommends here in this thread:

http://forum.grailtone.com/viewtopic.php?f=33&t=72555

 

[Dodgion556]

If your sound was a "strange sound, loss of power, or heavily distorted sound with a loss of volume" I'd look at a power tube. In fact the burning smell you are speaking of may indicate "Red Plating". Something got hot which was accompanied by noise and that could indicate a red plated power tube. When you shut the amp off that more than likely cured the physical short (Yes, I am paraphrasing page 38 of the Mark V35 owner manual).

In reality, I'd pull those power tubes and inspect each one, it's possible for a red plated power tube to leave heat marks inside the tube. If all of the tubes look the same and do not indicate that they were hot, then reinstall using the proper paring and color coding just like when you removed them. Mesa tubes are color matched so be sure to pay attention when removing.

I doubt it's a preamp valve. The burning smell you speak of happened to me in an older Fender amp that red plated one time, it's physically where the tube goes into self destruct mode and it stinks. Preamp tubes just don't have that kind of juice. Don't get me wrong a bad preamp tube can raise all sorts of trouble and noise, but the smell has me focused on a bad or going bad power tube.

Regardless, MESA is a phone call a way and I bet that if you called they would prolly send you a new set.

Hope this helps -and I hope you have great luck with your amp!

Cheers

 

[Dodgion556]

It's strange, but so far the hum hasn't come back. So, to summarize, it hummed, then it smelled like something got VERY hot, and now everything is just fine... odd. I ordered a spare set of tubes that I suppose I'll just swap out at the next sign of failure.

With my luck, the issue probably won't resurface until I take the amp to band practice or a show. :lol:

You probably want to swap out the bad tube before a failure. It's what Boogie recommends here in this thread:

http://forum.grailtone.com/viewtopic.php?f=33&t=72555

And BTW this is great advice and possibly money in the bank :mrgreen: