Bass 400+ blown fuse, what to check?

[Dr. Love]

I have a Mesa Boogie Bass 400+ that just popped the fuse yesterday while doing some low volume practice after about 30 min. There was a little bit of static shortly before the fuse blew.

Should I just replace the fuse, or could there be something more serious that needs to be checked first? I don't see anything is obviously fried, so I thought I would consult the experts here.

history: I got the amp in 1998 used, have never changed the fuse, tubes or had any work done on it. The last few years it has seen very little use, it's stored in the house and I just fire it up once in a while and play some to make sure it's still working. The cab is an 8 ohm GK 4x10. Nothing plugged into the effects loop, but i just noticed the effect level control was set to 10.

[whoatherechunk]

ok here's my story. had my mesa boogie for 5 years then all of a sudden the amp just stopped. checked the fuse and it was blown. i took my amp to a tech and well one of the tubes shorted out and i guess it caused some problems....that resulted in my retubing the whole power section. that was my experience. it always isnt just the fuse. take it to a tech and see what he says. simply replacing the fuse and playing might cause further problems/unwanted consequences.

[Foz]

Though popping a new fuse in might do the trick for ya, given how long in the tooth your tubes are I'd say a thorough cleaning and a once over by a competent tech is a good bet if you plan on relying on the amps at a show or some such in the near future. Wouldn't hurt to have him check tension on the tube sockets while he's in there checking your tubes and cleaning things up.

[JimmyM]

my rule of thumb is replace the fuse...if it pops again, then i know there's something wrong. if not, i ride it.

i agree with foz it's probably time to get it checked out. however, if it's a single bad tube, don't replace them all. just replace the one that's bad. if it's a bad power tube, try to get one that's got specs that matches your others. but don't be tricked into replacing all of them unless they're all bad (highly unlikely but it does happen sometimes).

[ridgeback]

like the lads say ..get it checked over...had a couple of fuses go on my own 400+ over the years..replace it. if its ok then dont worry to much..

[T-Bird]

Hi.

Originally Posted by JimmyM

my rule of thumb is replace the fuse...if it pops again, then i know there's something wrong. if not, i ride it.

It's usually the rule of thumb in the pro circles as well.

If the fuse filament is unsupported (just the wire in a glass tube), the constant vibration, bumps on the road, handling shocks etc. will eventually weaken the filament and it'll break. Yours have held at least 12 years, I would've changed it already twice.

Tubes that old (assuming non-NOS, Russian CP tubes) are most likely on their last legs also, so a trip to a tech is highly recommended in any case, even if the amp works with the new fuse.

Regards
Sam

[countrybass007]

I just ordered a new set of power tubes from Boogie for my D180. I do replace all six when I replace them. You've got twelve, so that would run you about $275. When a power tube starts acting up I figure it's time for a new set. That, of course, is if they haven't been replaced for a year or so. The trip to an amp tech is excellent advice, to make sure the problem is just a tube or two. Fuses do go bad and blow on occasion for no real reason other than they're worn out. My old Ampeg SVT used to blow a fuse every once in awhile, pop in a new 10amp fuse and it was fine.

[countrybass007]

A new set of power tubes makes your amp sound better too.

[anderbass]

Taking your amp to a good tech would probably be the best option, but my 400+ was intermittently blowing fuses simply because one of the power tubes had rattled nearly completely out of its socket. After pushing this tube back in It never blew another fuse.

If this is your problem you'll probably find evidence that the tubes pins have been arcing when they lost contact with the socket. (my tube had black soot and a very small melted spot on one of the pins that was only visible with a magnifying glass)

My loose tube was on the inner row and required either removing the amps top panel, or the back row of tubes to even see it.

The retaining clamps that are supposed to hold the power tubes in place on my 400+ were barley touching the tube bases, so while I had the tubes out I re-tensioned them all by simply squeezing each half closer together so they held good tension against the tube base.

One of my guitarist ran into this exact same scenario with his Twin Reverb amp at a gig one night. We pushed the power tube back in, (re-tensioned the clamp) and this amp is still currently working fine 10 years later.

[johnk_10]

if you don't know how to repair/sevice a tube amp yourself, the first thing i'd check is your wallet to make sure that it's full of cash before you take it to a tech that is familiar with high powered tube amps.

but seriously, i think that probably an output tube blew (along with it's associated resistor). i usually replace that tube and it's push-pull counterpart, and then save the other good one as a spare. .......of course, i'd check/replace any cooked resistors, and check the bias.

[Foz]

The 400+ has an 8 amp slo-blo fuse. Its a tough fuse and it takes a man sized problem to pop one... I wouldn't take it lightly as I doubt it just "wore out" on its own.

I bet you a doughnut you have at least one bad power tube and/or a dirty/loose power tube socket.

Before popping a new fuse into the box - at the least - I'd drain the caps, and then I'd flip the amp over and look at the bottom side of the sockets to assure that that all the looks right and then peek at the caps to assure that they are all pristine [no bulges or "leakage"] and sniff around for any dodgy looking solder joints [check the input/output jacks particularly and maybe give em a wipe with some Caig on a Q-tip].

Then flip it back up right and pull each power tubes one at a time, cleaning each socket [Caig Deoxit] as you go and looking for evidence of arcing and assuring that the tension of the sockets for each pin is good and tight before re-installing each PT. Also as you re-install make sure the tube retaining rings grab each tube base nice and tight as you insert em. If anything looked funny I'd stop and send the amp to the doctor. If all went well I'd try a new fuse.

If above procedure does NOT sound scary- then take it to a tech who is knowledgeable enough to give those caps the respect they deserve.

[Dr. Love]

Thanks for all the help, I'll replace the fuse first as a temporary measure, and make a tech appointment (once i find one here) to do the due diligence soon and make sure there are no further issues lurking. At least this way I have a realistic idea of what to expect when they check it out and give the "damage report".

[fpdeluxe]

Hi,
I too am an owner of a Mesa 400+. I love the amp like a beautiful but high maintenance woman. It is too temperamental for me sometimes. It actually weighs almost as much as my wife come to think of it.

I have recently bought a used GK 1001RB Mark II as a backup. Peace of mind, but not "my" tone.

I've had it for 7 years, playing through an Ampeg 8x10. I play it a lot, but I've never toured more than a weekend at a time with it. I run an extra fan back there to try to keep it cool. I have fuses blow once in awhile. I've replaced the tubes twice. I have a good friend who knows his way around tube amps so I kind of have an amateur tech for it. He plays through a vintage Sound City, so I trust him.

The worst thing that happened to me was that the fuse didn't blow when it should have and it burned up some stuff inside. My buddy had to rewire some parts of it because the tracer wire was totally burned. Since he fixed it I have been paranoid about it. We think we may have a bad transformer or something. Something strange happened a few weeks ago and I shut it down and am going to give it back to him to open up. It's a love/hate relationship, like that old Porsche I used to have.

On the good side - I get envious looks and comments from other bassists at gigs and people know we are a serious band when they see that thing. I can get tones like my heroes, McCartney, Entwistle, and Mick Grondahl (Jeff Buckley's old bassist who was the reason I bought it in the first place!) It's a special piece of equipment.

One thing I blame on myself is that I need a nice expensive shock mount case for it. I ran out of money before I got that, so that's my next purchase should I decide to take it out of the studio anymore. It's in a regular, though oversized SKB case. I thought that would be enough, but it seems to not be.

Thanks for reading!

[Foz]

I need a nice expensive shock mount case for it

Sigh... yeah i should do that - or just leave it in the studio and let it turn into a hanger queen... sigh.

[Dr. Love]

Well........... I got a chance to take a more thorough look at the amp again this evening. The tubes had dust on them, so i wiped the haze off an found this:



the ugly looking tube in the rear also appears to have a crack near the base, just below the "47" on the label. The tube in front of it looks like the label is about burnt up..



yup... repair shop time.

[B-string]

Left tube, classic loss of vacuum (gassy) tube, right tube has been running too hot. Be sure to put those back in the same sockets when you take it in. Any clues a tech can get puts you miles a head!

[T-Bird]

Hi.

With the additional information there's only one course of action: tech time.

DO NOT replace the tube(s) or the fuse and try to power the amp up, let the tech take care of that.

And do follow B-string's advice to put the tubes back to their original positions to aid the tech.

Regards
Sam

[calebbarton]

Originally Posted by Dr. Love

I have a Mesa Boogie Bass 400+ that just popped the fuse yesterday while doing some low volume practice after about 30 min. There was a little bit of static shortly before the fuse blew.

Should I just replace the fuse, or could there be something more serious that needs to be checked first? I don't see anything is obviously fried, so I thought I would consult the experts here.

history: I got the amp in 1998 used, have never changed the fuse, tubes or had any work done on it. The last few years it has seen very little use, it's stored in the house and I just fire it up once in a while and play some to make sure it's still working. The cab is an 8 ohm GK 4x10. Nothing plugged into the effects loop, but i just noticed the effect level control was set to 10.

Mesa printed the INCORRECT fuse value on my 400+. I changed it to the correct value and haven't had a problem since. Might do a search for the correct value as i cant remember off the top of my head.

[B-string]

I show an 8amp slo-blow for 120vac, 4 amp slo-blow for 220vac on the schematics I have.

[Dr. Love]

Thats what mine shows too: 8 amp 120v slow blow.