Recently acquired Mesa 400 Problems

Zildjian106 · #1 12-13-2011, 06:45 PM

So I picked up a used Mesa 400, I did not have a cab to test it with at the time, and I bought it on the spot. I brought it home a week or two later, to find something funky is going on with the amp. Its making very weird nasty noises, and I figure it needs new tubes, as I look at the tubes I notice the far right tube is not lit.

Called the guy up, told him what was going on, he asked if it was the far right tube, as it was slow to "warm up". Anyways he sends me a little bit of cash to put towards new tubes. I bought a sextet of 6l6's swapped them out. Turned on the amp, then flipped standby. The right tube lit up a bright blue/white and the amp went dead.

What could possibly be wrong with this amp?

johnk_10 · #2 12-13-2011, 06:53 PM

it could be alot of things. IMO, it's time to take it to a qualified tech.

solodb · #3 12-13-2011, 06:56 PM

Do what johnk10 says. You got a great amp and it's worth getting in tip-top shape by a reputable tech.

Mykk · #4 12-13-2011, 07:00 PM

I had a Mesa 400+ that did the same exact thing. After taking it to three different amp techs (two in Cali, one in Az) and almost a grand paying "techs" with no improvement I eventually traded it in on an Ampeg cab.... the shop (knowing of the problems I've had with this head) than sold it on Ebay.

Good luck.

RickenBoogie · #5 12-13-2011, 07:30 PM

Yes, you need an amp tech, period. Have you been running it without a load connected? (speakers)

Downunderwonder · #6 12-14-2011, 12:34 AM

I've been reading up a bit about Mesa tube amps lately. I'm no amp tech at all but they seem to do things a little 'differently' so it's not surpising that three "real amp techs" would fail to fix one.

Here's an idea: if you send it to Mesa with your sorry tale I'd be surprised if they charged you much more than the parts to fix and send it back. They seem like that kind of company. Of course I could be completely wrong about that. And if the parts include a transformer or two you are going to be out of some big money.

Zildjian106 · #7 12-14-2011, 10:41 AM

Well I messed up, I realized my poor focus last night landed me my dead amp. I unplugged the cab, so I operated it without a load, thats why this happened. The amp wont even turn on now so I may have done myself in on this one. I just hope there is no damage to the amp. Oops

Low Class · #8 12-14-2011, 10:58 AM

Quote:

Originally Posted by Zildjian106

Well I messed up, I realized my poor focus last night landed me my dead amp. I unplugged the cab, so I operated it without a load, thats why this happened. The amp wont even turn on now so I may have done myself in on this one. I just hope there is no damage to the amp. Oops

You may just blown the fuse.

coreyfyfe · #9 12-14-2011, 11:07 AM

Quote:

Originally Posted by Low Class

You may just blown the fuse.

+1, if it was just the output transformer the amp would still power up. Sounds like you had a component fail in the power section that caused the fuse to blow.

BassmanPaul · #10 12-14-2011, 11:14 AM

As advised earlier, take the amp to a tech and have it checked over. It's the best thing you can do.

James Judson · #11 12-14-2011, 11:50 AM

Check the fuse. If it's blown go get some more fuses (like ten of them). Yank the tubes and replace the fuse. Does the fuse blow? If so its tech time. If not replace one tube and turn on. Does the fuse blow??? Continue this pattern til you find the bad tube. It is common for tubes to short out internally and blow fuses. It is also common for components to short and blow fuses.

It is common for non "TECHY" people to be paranoid of electronics and warn that you can be killed poking around with electricity. A tube amp does have 300-400 volt power supply. I say if your not sure where the voltages are or you have a condition (weak heart, pace maker etc.) put one hand in your pocket. That way if you do touch electricity it will go in one arm down your leg and bypass your heart. Won't feel "GOOD" but won't be lethal. Rule of thumb: Tubes, fuses, knobs, etc are external and most anyone can safely swap these things. If you need to use tools to open it up, "know what your doing".

James Judson · #12 12-14-2011, 11:51 AM

Quote:

Originally Posted by coreyfyfe

+1, if it was just the output transformer the amp would still power up. Sounds like you had a component fail in the power section that caused the fuse to blow.

Shorted out output transformer will blow fuses.

James Judson · #13 12-14-2011, 11:57 AM

Quote:

Originally Posted by BassmanPaul

As advised earlier, take the amp to a tech and have it checked over. It's the best thing you can do.

A tech is just someone that is not afraid to open her up. All techs are not created equal. I've seen techs that do more harm than good. When you do find a good one however take care of him, he's worth his weight in gold.

Actually I like bad techs. They screw up an amp. The amp goes to a pawn shop. I get it for less than $100.

BassmanPaul · #14 12-14-2011, 12:18 PM

Quote:

Originally Posted by James Judson

A tech is just someone that is not afraid to open her up.

If you consider this to be true you are doing ALL tube techs a disservice. No one who has no base in high voltage electronics should be opening the case of a tube amp. Advising some such person to do so is foolhardy at best!!

RickenBoogie · #15 12-14-2011, 12:22 PM

Very Big +1 to that^.

Downunderwonder · #16 12-14-2011, 12:36 PM

If OP hasn't got nouse to not unplug cabinet he should leave it well alone. I once saw a guy with 140 IQ get a zap off a fuse when he thought the fuse was gone and neglected to unplug the power.

BassmanPaul · #17 12-15-2011, 12:03 PM

Quote:

Originally Posted by Downunderwonder

If OP hasn't got nouse to not unplug cabinet he should leave it well alone. I once saw a guy with 140 IQ get a zap off a fuse when he thought the fuse was gone and neglected to unplug the power.

Even geniuses make mistakes! I know! I've made a few myself!

Sneakypete · #18 12-15-2011, 01:54 PM

I've been working in electronics for forty years or more and have NEVER made a mistake. Well, not more than eight or nine hundred times anyway. It's always good to learn something new but just trying this and that without at least a multimeter and a basic grasp of circuit theory is unlikely to be useful. Take it to someone who knows what they're doing and when it's fixed ask him what was up. IME good techs are usually happy to discuss their work with someone who is genuinely interested. Especially true of someone who works in the warm, wonderful world of thermionics!

Zildjian106 · #19 02-13-2012, 02:02 AM

So it turns out the replacement power tubes I put in were bad...

I just got it to work again about an hour ago, so happy! Just plugged in the old mesa tubes with 2 JJ 6l6's and it powered right up. I also swapped out the 12ax7's.

When I flicked standby I was hoping for the worst, thankfully no tubes blew up.

Im super happy my bass 400 is kicking again!!!