Mesa 400+ advice?

Naggon · #1 12-23-2011, 12:03 PM

Hi,
I recently bought a Mesa 400+, and it is absolutely fantastic, I love it. I've kept it in my jam space, haven't moved it around or anything, but yesterday I went in to jam, and for some reason it just won't make any sound at all. I just can't figure it out, and I'm totally stressed! I've searched through tons of past threads for something similar without any luck. My amp powers on just fine - the power light goes on and the tubes fire up, but it is not making any sound AT ALL - no hum, no fuzz, no crackling...nothing.

I'm running it into a 4 ohm 4x12 ...I've also tried it at 8 ohms, with no luck. I'm running my bass straight into it, nothing funny. The fuse is good, and all the tubes look fine, and the fan runs fine too... No, its not on standby. I've checked my patch cable and speaker cables, and its not my bass either. Its always been plugged into a power conditioner, so I doubt its anything weird with the voltage, and I also checked the breaker on the power conditioner, and that's ok. EQ's on the Mesa are all pretty close to flat, I've never run it on any crazy settings. I've checked the speakers in my cabinet, too, and they're fine....

I can't think of anything else to try! I sold nearly everything I own and literally took a second job to afford this amp, so I'm terribly worried about it! Any advice would be greatly appreciated, so thank you kindly in advance.
Cheers!

bobunit · #2 12-23-2011, 12:09 PM

Quote:

Originally Posted by Naggon

Hi,
I recently bought a Mesa 400+, and it is absolutely fantastic, I love it. I've kept it in my jam space, haven't moved it around or anything, but yesterday I went in to jam, and for some reason it just won't make any sound at all. I just can't figure it out, and I'm totally stressed! I've searched through tons of past threads for something similar without any luck. My amp powers on just fine - the power light goes on and the tubes fire up, but it is not making any sound AT ALL - no hum, no fuzz, no crackling...nothing.

I'm running it into a 4 ohm 4x12 ...I've also tried it at 8 ohms, with no luck. I'm running my bass straight into it, nothing funny. The fuse is good, and all the tubes look fine, and the fan runs fine too... No, its not on standby. I've checked my patch cable and speaker cables, and its not my bass either. Its always been plugged into a power conditioner, so I doubt its anything weird with the voltage, and I also checked the breaker on the power conditioner, and that's ok. EQ's on the Mesa are all pretty close to flat, I've never run it on any crazy settings. I've checked the speakers in my cabinet, too, and they're fine....

I can't think of anything else to try! I sold nearly everything I own and literally took a second job to afford this amp, so I'm terribly worried about it! Any advice would be greatly appreciated, so thank you kindly in advance.
Cheers!

Try running a patch cable from the send to return on the fx loop. Sometimes they can be fussy.

chillerthanmost · #3 12-23-2011, 12:27 PM

Phase Inverter tube. Find it, replace it, power on. This just happened to my Univox. Some tubes just fail sometimes.

Naggon · #4 12-23-2011, 12:42 PM

Tried running a patch cable through the FX loop, no luck, but thanks for the idea.

I guess it totally could be the phase inverter tube! I'll see if I can pick one up, and then update this thread when I find out if it works.

Thanks a lot!!

anderbass · #5 12-23-2011, 12:53 PM

Does your bass have a battery? (maybe its dead...)

How did you confirm your cab or speaker cable is good? Do they both still work with another amp?

Quote:

Originally Posted by bobunit

Try running a patch cable from the send to return on the fx loop. Sometimes they can be fussy.

+1, good suggestion, try this test with both the front and back fx-loops. Then if it still wont play you could also try plugging your bass directly into either of your amps return jacks as an easy test to bypass your 400+ preamp section.

Naggon · #6 12-23-2011, 01:08 PM

No battery, my bass is passive.

Quote:

Then if it still wont play you could also try plugging your bass directly into either of your amps return jacks as an easy test to bypass your 400+ preamp section.

Cool idea, but unfortunately no luck there...

I just found a place in town where I can buy a phase inverter tube for $17. Gonna head out shortly and give it a try!

chillerthanmost · #7 12-23-2011, 01:17 PM

Check yours for a leak or glow. It's v3.

Quote:

Originally Posted by mikeldtl

The preamp tubes are laid out like this:

Looking from the FRONT, with the knobs and input jack facing you:

V1 is nearest the input jacks. This tube is common to both of the preamps. On mine it is snugged up against the transformer and with the stock Mesa tubes it was the only one without a rubber jacket.

V2 is the next one over to the left, this drives the tone controls.

V3 is the phase inverter, one over to the left again.

The last tube on the far left, when looking from the front, is V4 and is the driver tube.

I have confirmed this by taking off the bottom plate of the chassis. If you take off the plate each tube is labeled clearly on the PCB (V1,V2, etc.) with a small silkscreen and the sockets are mounted directly to the PCB. So, if in doubt, take off the bottom plate and the label on the PCB corresponds to the respective tube socket. Hope this was helpful.

Naggon · #8 12-23-2011, 02:08 PM

Hmm. So, I've opened 'er up and checked out my phase inverter tube. Haven't replaced it yet, but it looks okay to me. Pictures are attached. (sorry for the poor quality, had to use my webcam) I'm not that familiar with blown tubes, how common is it for tubes to go without any visible sign?

Do you think I still aught to replace this tube? If so, I'll do that asap then post pics.

Cheers!

chillerthanmost · #9 12-23-2011, 02:31 PM

From the pics alone, I can't guarantee that the PI is your problem. I would personally swap out the four preamp tubes but I'm also a huge fan of good, old, preamp tubes.
If you're confident that it's not your cables, cab, bass, etc, and you're sure you've tried all the inputs, with the eq on AND off and there's absolutely no audio what so ever than it's to take it to a tech. Could be a transformer (let's hope not), a simple power/preamp tube change (which could cost just as much as a new tranny), a lose tube socket, etc.

I'd swap the tubes and clean the inputs and pots before taking it in but I also don't have a local person that can help me diagnose problem. It's your call. Good luck.

JMarkD · #10 12-23-2011, 02:42 PM

You probably checked this, but there are two knobs in the back of the amp for the loop and DI level. Make sure they are both turned down. If the loop knob is turned up with nothing in the loop, no sound, if I recall.

Naggon · #11 12-23-2011, 02:56 PM

Quote:

You probably checked this, but there are two knobs in the back of the amp for the loop and DI level. Make sure they are both turned down. If the loop knob is turned up with nothing in the loop, no sound, if I recall.

Checked that, no dice, thanks though.

Quote:

From the pics alone, I can't guarantee that the PI is your problem. I would personally swap out the four preamp tubes but I'm also a huge fan of good, old, preamp tubes.
If you're confident that it's not your cables, cab, bass, etc, and you're sure you've tried all the inputs, with the eq on AND off and there's absolutely no audio what so ever than it's to take it to a tech. Could be a transformer (let's hope not), a simple power/preamp tube change (which could cost just as much as a new tranny), a lose tube socket, etc.

I'd swap the tubes and clean the inputs and pots before taking it in but I also don't have a local person that can help me diagnose problem. It's your call. Good luck.

I guess its time for that. Damn, I was hoping it wouldn't come to this, the techs around here are all total jerks, unskilled (they've screwed up stuff I've brought in in the past just as often as fixing them), hugely overpriced, and massive wait times. Guess that's just the way she goes.

Really appreciate all the advice, fellas. If you have any other ideas for me to try, I'm all ears. If you think better pictures would help anyone diagnose anything, I can make that happen.

Cheers!

Downunderwonder · #12 12-23-2011, 06:13 PM

There may be some more fuses to check than just the main one.

There's a thread for recommnded tube amp techs. There might be one in Canadaland eh! If it comes to it, you would be better off sucking up the freight to get it to a good tech than suffering at the hands of a bad one.

Muldoon · #13 12-23-2011, 08:37 PM

Check the switch that turns the graphic EQ on and off. I had mine in the middle once and no sound.

walterw · #14 12-23-2011, 10:25 PM

have we confirmed that another amp works with that speaker cable and cab?

Caca de Kick · #15 12-23-2011, 10:44 PM

One last check, with amp in run mode with cab plugged in, look at all your tubes. Besides the power tubes glowing, are the preamp tubes glowing too, or not?

Naggon · #16 12-23-2011, 11:23 PM

Quote:

There may be some more fuses to check than just the main one.

Hmm, I did not realize this. I'll look for a schematic and see if there are others...

Quote:

Check the switch that turns the graphic EQ on and off. I had mine in the middle once and no sound.

Checked that, in both positions, with no luck. Thanks for the suggestion though.

Quote:

have we confirmed that another amp works with that speaker cable and cab?

Yes.

Quote:

One last check, with amp in run mode with cab plugged in, look at all your tubes. Besides the power tubes glowing, are the preamp tubes glowing too, or not?

Yes, the preamp tubes are glowing as well. Its a beautiful sight - I'm looking at them right now with the lights off, all 16 tubes glowing... I love it, just wish it would give me some sound!!

Naggon · #17 12-23-2011, 11:39 PM

WOAH!
Something really weird just happened.
I've been sitting here with the amp on and the tubes fired up for probably twenty minutes, and I just decided to plug in one last time just to test it. I plugged in my guitar instead of my bass, just because it happened to be closer to me, and my amp made some sound! It was really quiet (considering how loud it should have been - I had the channel 2 vol. at about 6 and the master at about 4), quite dirty, and just faded right down to nothing over about five seconds. Try as I might, I haven't been able to get it to make any sound again.

I'm totally stumped. Does anybody have any idea what this could mean???

Downunderwonder · #18 12-23-2011, 11:59 PM

Bad guitar cable.

Downunderwonder · #19 12-24-2011, 12:00 AM

Bad input jack conection.

walterw · #20 12-24-2011, 12:02 AM

stop!

at this point you could be further damaging the amp.

unplug it and take it in to a tech, you've exhausted the "user serviceable" part of the program (unless you wanted to go out and buy all new tubes for it $$

$