Love the sound but am getting discouraged...

[wackocrash5150]

After many hours of reading and listening, I decided in January to finally buy a dual rec as my local dealer had the NOS 2009 models on blowout. Got it home, still sealed in the box, plugged it in, no joy. Actually was getting a jolt when touching the patch cable. Oh well. ***** happens and maybe it was built on a friday afternoon.
Got a replacement and had them test it there. Worked fine. Had it about a week and then realized that the new "Reborn" MKII models had a few more options and came with a very nice Jute Grille option. So I retuned the working one and placed a special order for the MKII. The cost wasn't that much more in the grand scheme of things.
Three months later my special order arrives. Again I had them run a quick test on it before I arrived. Picked it up, went to rehearsal space, plugged it in .... HEAVEN!!!! Sounded amazing just straight into the front. Went back two days later with my TC Electronics G-Major in hand and changed nothing with the exception of the G-Major running in the loop. I noticed that the output with the loop on was quite low. I figured "fine" and that I just had to tweak the levels. Next thing I know there's this horrible low-end feedback effect happening. Put the amp in standby and double checked connections. All was ok that way. Turned loop off and all seemed fine for about two minutes. Checked everything again, turned loop on and hit a few muted E chords. Same low end feedback. Maybe a problem with the G-Major so I disconnected and turned loop off. Sounded fine but a little gritty and muffled. Hooked up a regular Digitech Delay in loop and levels were fine. Sounded ok but still kinda gritty. Then I noticed some clicks and pops on the red and orange channels so i changed from my wireless to a good patch cable. Same thing and I was occasionally able to reproduce the feedback. I even switched cabs thinking it might be that. Then by fluke I happened to bump the amp and it made a noise like someone kicking a mic stand with the mic on. By this point in the night the amp sounded quite muffled and gritty. Any ideas? Bad tube?

 

[espboogie123]

Remove tube shields. With amp in play mode, amp on with standby off and some volume applied, tap the tubes with a wooden stick or eraser end on a pencil to check with one is the culprit. You will hear a crackle/ring/pop. Tap/check the power tubes and preamp tubes. It could be that a tube went bad during shipping process or the tube just straight up failed. Happens all the time. Some tubes are stronger than others even though they were new.

Refer to this Mesa troubleshooting video:

http://www.youtube.com/watch?v=wSl-l9aWDHw

 

[screamingdaisy]

Sounds like one of the tubes has had a mechanical failure (ie, something inside the tube is loose). Do the tap test above and it should be relatively simple to diagnose. Mesa has a 6 month warranty on tubes so take it to the store where you bought the amp and exchange it for a new one. Maybe grab a few spares while you're there.

 

[wackocrash5150]

Thanks for the advice. I suspected it might be a pre tube but wanted to put the feelers out to see if I was on the right track. It was just odd that it sounded killer the first time I fired it up. Perhaps the first heating/cooling cycle finished it off?

I'll start whackin tubes with an eraser and report my findings back. lol Thanks guys.

 

[screamingdaisy]

Could've been.

I've had a number of new amps over the years and most of the tube headaches usually happen right off the bat... probably due to vibration while shipping or something. Once I get the initial tube problems out the way it's usually smooth sailing.

 

[droptrd]

Yeah dont get down about a bad tube. It happens. But it does sound to me like a preamp tube is the culprit

 

[wackocrash5150]

Ok. So I took the chassis out of the case and fired it up under load. I then removed the pre-tube covers and pretended I was a drummer. v3, v4 and v5 all seem fine. Almost no noise when I tap them. v2 is very loud particularly on the side closest to v1.

Still pluggin away on it....

 

[screamingdaisy]

Hit the power tubes as well.

 

[espboogie123]

Cool. Report your findings. What about v1?

 

[wackocrash5150]

Well it seems those tubes should sound louder as they are in the gain stages. (I'm learning as I go)

Regardless of what tube I put in what position, it still does it. I'll start by just lightly tapping the chassis and the sound gets louder and louder till it squeels. It might sound like I'm hammering on the chassis but i'm not. I imagine that when jamming the other night, the vibrations from the cab triggered it in much the same way my hand did. I'm uploading a YouTube clip as I type. Will post link if i'm able.

 

[wackocrash5150]

Here it is. Hope it helps.

http://www.youtube.com/watch?v=QmVbrH7U3no

 

[droptrd]

Oh yeah thats a preamp tube for sure IMO. Swap out V1 and see what happens.

 

[wackocrash5150]

Swapped out with an EH in v1 and a JJ in v2 ... same result. :s

 

[droptrd]

OK. Then put the original tubes back in and swap out V3 and V5

 

[droptrd]

Then if no change swap out V4. Has the loop been on or off during you testing. IIRC the 3 ch rectos have V4 as a loop buffer.

 

[wackocrash5150]

Went one further. Took the known working 3 tubes from my classic 30 and used em. So now all pre tubes and still same result. Odd thing I noticed. I tap it to get it squeeling and it keeps going sometimes. If I lightly press the chassis in front of v3, it stops.

The loops has been both on and off.

 

[espboogie123]

the same in both 50w and 100w modes? what channel are you running these tests in. Check all channels.

 

[wackocrash5150]

Does it in Orange and Red channels in both 50w and 100w. It's almost like something is loose or a hair away from shorting on the chassis. (my best guess anyway)

 

[wackocrash5150]

Well I contacted my dealer and they're going to take care of it and give me a loaner in the meantime. I'd put more effort into this if the amp was a few months old but I just got it last week. When I get it back I'll post on here what the diagnoses was. Thanks for everyone's suggestions.

Cheers

 

[droptrd]

Bummer man. Hope it works out for you. Luckily you have the warranty.