Mesa/Boogie 400+ problems

[e_bass_guy]

Hey everyone. New to Talk Bass and wish I joined sooner.

Anyway, about a year ago I purchased a Mesa/Boogie 400+ with a matching powerhouse 4x10 for $500. (I know. A friggin deal) Most of the time I've owned it, there were intermittent times when crackling sound was coming through the speakers. The owner said that the tubes weren't even a year old when she sold it to me. Mesa tubes. I swapped the preamp tubes and the problem went away. The only issue after that was if the master was turned past 6 or 7, it would make a awful noise. I never needed it that loud anyway, so I ignored the problem.
Fast forward to a month ago. Playing a gig, it started to make an awful noise again out of nowhere. Turned off the amp and turned it back on, the noise continued even with the master and gain at zero. When the stanby is off, it's just fine but once it gets switched on, an awful electronic bazzsaw noise.

Anyone have similar issues or have any ideas. I've heard that these amps have caused problems but I really love it.

Thank you

 

[agedhorse]

Give customer service a call.

 

[e_bass_guy]

I did so already. I went through the steps to test the 6l6s to see if the tubes were bad. They all seem to check out. Their suggestion was to take it to an authorized dealer. We have one in our area but I haven't heard great things about them.
I'm trying to repair it myself. I have fairly decent electrical knowledge and cash is super tight so I'd like to fix it myself.
Any amp tech guys out there that can help me out on this one?

 

[agedhorse]

I'm going to recommend against this. Without appropriate test equipment, knowledge about these amps AND experience repairing them you run the real risk of causing additional damage. I see it all the time.

Also, there are some lethal voltages inside your amp.

 

[e_bass_guy]

Yes I am aware of this. I've worked on amps before and all with success. This one just has me stumped but the last thing I want to do is mess something up. I may just suck it up and take it to a tech.
Now my question is if anyone else has had a similar problem or other probelms with the Mesa/Boogie 400+? I've heard of mixed feelings about the quality of construction and design of the amp.

 

[twinfallsbass]

Could it be a preamp tube starting to go bad? I believe all four are 12aX7's, do you have spare 12aX7's lying around?

 

[twinfallsbass]

I've heard of mixed feelings about the quality of construction and design of the amp.

I have never heard mixed feelings on the quality of the 400+ and I have been on this site since '98 or so. I've had my 400+ since '98, besides having to replace the power tubes and a few preamp tubes, mines been plugging along with no issues. I would not worry about the 400+ at all. Once you get it fixed properly, you'll be glad you have it

 

[e_bass_guy]

Preamp tubes are good. I love the amp. I was an Ampeg guy for a long time but I got this sweet amp and couldn't resist. The Mesa is a bit diffrent but was easy to get sweet tones from. And the power?! Lol. Just an awesome amp.

 

[twinfallsbass]

Plus you got a smoking deal on that combo. I thought I got a good deal at $450 for mine back in '98

 

[BogeyBass]

could be alot of things. could probably fix it to stop oscillating if thats the problem. then again probably time have good run over and address things now so alot of small problems dont come up over time. get a run through with it open. so could be tech time thats trusted to do a good touch up on alot of things. lead dress/ board touch up/ sockets , phase splitter, phase split caps, bias, plate screens, power tubes etc etc. usual suspects for self oscillation. nothing can be said only guessing on the internet without test equipment.

 

[agedhorse]

OR, simply have your amp go through proper and complete diagnostics, that way what is REALLY wrong gets fixed without guessing.

If you bought it used, it also needs to be checked for improper repairs, modifications and other crap that internet and hack techs tend to do when they run out of proper troubleshooting skills. Correcting other tech's and tinkerer's work is (unfortunately) fairly common these days, and it's a LOT more costly than simply repairing the amp in the first place.

 

[JW56789]

I am a Certified Graduate of the 'It Worked Fine Until I Fixed It' course. So, don't be me.

You stole that amp and cab, and if it were me I would do my homework, find someone well and truly qualified, and spend a little of the money you DIDN'T spend on the purchase and make this thing right. 400's last a LONG time if they're cared for by the right tech going under the hood when required. If he's a good guy and you ask properly, I've found guys like that to be a tremendous resource for the little tips they'll give to someone genuinely interested in doing it as right as they do.

Aged would have had me at the 'lethal voltage' part . . . .

 

[kulit17]

I did so already. I went through the steps to test the 6l6s to see if the tubes were bad. They all seem to check out.

i've owned 3 400+ and all were built like tanks. my first 400+ i owned though, i did have noise issues and took it to an authorized repair person. a couple of my tubes ended up being microphonic so i ended up needing to replace them.

just curious, what steps were taken to determine that your tubes "checked out"?

 

[beans-on-toast]

Google elpaso tube amps mesa 400+ Youtube, there are a few videos where the tech is struggling with a 400+ repair.

I’m not suggesting you try his solutions, but rather am attempting to demonstrate how complex resolving this issue in the 400+ is. There are many potential issues to address. In the end, with his changes, he seemed so happy that he found an EQ setting that wouldn’t send the amp into oscillation. Not a proper fix as far as I’m concerned.

It stresses the need to find the right tech that knows this amp.

The fist thing that the amp needs is a general servicing. Cleaning the tube sockets, re-tensioning them if necessary, cleaning the jacks and their shunts (EQ), cleaning the pots. Then readings have to be taken to determine if the amp is operating within spec.

Concerning the tubes, a well matched set is very important in this amp. The set may have an issue. The tubes might test good but also important is how closely matched the cathode currents are and the tube’s transconductance at the operating plate voltage and bias. A good tech can do this or you can send them out to be tested (tctubes.com vintage vacuum tubes).