Ace Intermittent problem.....You guys should love this!

[Old BF Shred]

You guys should love this!

I have been having a very intermittent problem with my (approx) 1 year old Ace head.
And this started within a 2-3 months of purchase.

About every 2-4 weeks the output drops when coming out of stand by.
It does not have to be hot…it has happened when I first turn it on. And I always allow 3-5 minutes to warm up filaments. I run this amp with a variety of cabs all rated for proper impedance for the amp. Problem has happened with all of them.

It can happen after hours of playing….virtually always when going to standby and then coming back out.
I can’t really recall this happening while I’m playing, but my memory isn’t what it used to be…(a case of CRS)

As I am an electronic technician of 30 years experience, I have made some basic checks and tests when I
notice the problem. However, Mesa won’t give me a schematic or voltage charts, and after all, I don’t want to get too involved as it is under warranty.

I have talked to “George”, Mesa’s main stiletto tech and he is unsure as well. I have a Mesa service station not too far away, but it is so intermittent they also recommend waiting ‘til it gets to be more frequent as
“there is no sense tying it up for 2-3 weeks and not being able to duplicate the problem”…..I agree.

So I am curious if any one else has seen these symptoms….

It will reduce the output by about “half” (very subjective, but that is what it seems). Also sounds more distorted, even in clean channel/modes. Possible to turn it up and still get pretty loud.

To clear it up usually requires turning the amp off for a few minutes, turning back on and problem goes away for another few weeks. (I said intermittent!)

I have bypassed the FX Loop (even pulling out v4 to do this, as the bypass allows, so it isn’t the problem). I have tried running straight into the power amp (FX return….although v4 has to go back in for this).
I have replaced EVERY tube at least once, including 5u4 rectifier

Problem always comes back eventually.

I have isolated it to the power amp section or possibly power supply (BTW, screen grid resistors look OK, but can’t measure resistance as I don’t know what the value should be….Mesa won’t tell me squat diddly). Also if I pull one of the power tubes, the out put won’t drop as much as during the problem symptoms (logic being that I’m losing one side of the phase inverter/driver tube, but I have replaced it anyway).

I am hoping someone knows what this is so I can at least tell the service station to help expedite repair.
Neither they or Mesa have heard of this one (yet).

I am a big Mesa fan, but this has been a bummer (I have to take my trusty Crate Power Block to gigs as a spare…yuk)

Any help and insight is appreciated.
Otherwise, I am very impressed with what this amp can do when it’s healthy.
Thanks in advance!

 

[Jak0lantern01]

Grrrr.....Unless I missed something, you didn't mention if you were running on silicon or rectifier, which channel (clean or dirty), fluid or spongy, etc. You changed all of the tubes? Power, preamp, and rectifier? Need more info on this one.

 

[MusicManJP6]

This may offer some guidance. The key point to pull out of the following thread is that the Chinese tubes are supposed to work better than the Russian tubes...

http://forum.grailtone.com/viewtopic.php?t=25102&postdays=0&postorder=asc&start=0

Does it seem to matter if you are using bold or spongy power setting?

 

[Old BF Shred]

Oh, thought I covered everything...good point guys...it has happened in Spongy as well as full pwr (bold) and with either rectifier configuration.

I have eliminated all preamp tubes by running my Pod XT direct into FX return. And, as I stated, I have eliminated v4 as well, as is "supposedly" unique to the stiletto, you can bypass FX loop, pull out v4 and amp still works.(TRUE bypass).

Problem has still happened under both these scenarios. (and I was just lucky to get it to act up long enough for me to try all this before it cleared up....usually takes weeks to get it to repeat, but amp was quite warm when this occured (and it does'nt have to be...), and problem persisted long enough to isolate it to pwr amp section; a lucky break!)

The most "consistent" (barely) affect on this is replacing driver tube v5; 3 times now just to be sure, w/ both chinese and russian tubes, but since I have to kill power to change it, could be coincidence after amp cools slightly. What are odds of 3 bad drivers? Also I have put the old tubes back in & have it work perfectly again, so.....

Is this amp known to be brutal on driver tubes? Mesa says no....(of course).

I have also heard about the Russian tube issues in v3 and v4 (cathode follower) positions, but these have been eliminated, as I stated above.

My concern is that it may be a coupling capacitor, in pwr section, on the verge of dying and it could be this intermittent for a very long time before it goes completely. Yike! ...Or even filter cap in power supply...


Thanks for your responses, i will post the solution when we finally find it. Or when Mesa buys me a new amp (just kidding!...it will likely get worse and more frequent, then they can easily find the cause).

 

[Old BF Shred]

Update! Well it took 3 more weeks for symptoms to show up again after the last (and 3rd) replacement of v5 (PI, output tube driver).

Then one day, noticed amp was really hot....looked in back and saw slight orange glow on one of the el34's plate (mesa str 447). Checked idling current (bias) it was approx. 65 ma (should be 38-40 per Mesa). Yikes! :? :shock:

I could even pull out v5 completely to eliminate any signal or noise getting to output, and it still did it! It's in the shop now......I tend to think it may be defective output xformer...would explain a lot, especially being so intermittent.

Hopefully it will be right when I get it back (ETA 3 weeks ). I will finally know how the Stiletto is supposed to work ; only took over a year! :shock:

They should refund some of my money for all my grief (yea, right! :lol: )

 

[Old BF Shred]

Latest Update......got a call from the repair shop today. They finally got the amp to act up. Took 6 weeks :shock: for them to duplicate the symptoms. (now they know how I felt :x ).

Cause: a bad filter capacitor in power supply. They need to order the part from Mesa.
That could be another week or two, but at least they found something.

After 15 months of grief, it looks like I will finally have the amp I paid for.
I don't really blame Mesa because it can happen to any amp out there....just don't like it when it happens to me!

I just hope this is an end to my Stiletto issues....or I'll sell it and buy something else! :|

 

[Stratocaster]

Old BF,

Sorry to hear that it took so long to isolate, but that was an excellent job you did of troubleshooting a 'black box'.
I hope the amp is back in your hands quickly, and the two of you have many trouble-free hours ahead.

Thanks for posting a follow-up on this. Never know if it will help someone else down the road (as I'm sure you realize).

Strat

 

[Old BF Shred]

Old BF,

Sorry to hear that it took so long to isolate, but that was an excellent job you did of troubleshooting a 'black box'.
I hope the amp is back in your hands quickly, and the two of you have many trouble-free hours ahead.

Thanks for posting a follow-up on this. Never know if it will help someone else down the road (as I'm sure you realize).

Strat

Thanks, Strat. That's the great thing about a forum like this....my experience may save someone else some time and pain finding a solution for what may be the same or similar problem.

And likely, my Ace will be OK from here on.
This is my 4th Mesa, and they almost never have any problems (occassional tube replacement excepted).

Guess it was just my turn to run into a problem like this!
Take care!

 

[R_ADKINS80]

I just posted a very similar inermittant problem I have been having on my Triple Rec only when on spongy setting. VERY low volume and I have to crank the snot out of it to get good volume and even then, low end and gain is severely lacking. I've tried all 4 sets of power tubes I have and swapped all preamp tubes several times. Each time I replaced something it went away and I figured i solved the issue. However, after a few minutes of play and I get a HUGE volume drop. Until I get it figured out I have to play on bold. Doesn't matter tube or diode rectification. Me and Mesa are stumped.

 

[boogiemon]

What about the power coming out of the wall? This happen in more than one location?

 

[R_ADKINS80]

I actually just got it in me to pull out my volt meter and check wall voltage as the problem occurs....I got to thinking and it sounds like "super-sag" going on where maybe i'm getting even more sponginess going on than is supposed to be. If that is a problem, would a power conditioner solve this?

 

[boogiemon]

A voltage regulator would do it but the good ones tend to be expensive. Most conditioners just prevent spikes & don't help much for sags. That said, better to have one than not.

g'luck,

I actually just got it in me to pull out my volt meter and check wall voltage as the problem occurs....I got to thinking and it sounds like "super-sag" going on where maybe i'm getting even more sponginess going on than is supposed to be. If that is a problem, would a power conditioner solve this?

 

[R_ADKINS80]

Well, I hooked up my voltmeter to the same wall outlet as my Triple last night and fired it up to play. Sure enough, after about 15 minutes on spongy I got a loss of volume and overall a$$ in my amp. I looked at the voltmeter and it was reading good voltage at 118v. I switched rooms and got the same results. Flipped it back and forth between bold and spongy and and I have to compensate volumes by at least a 1/4 turn to match volumes between the two. Called my buddy up that has a Triple and had him do the same to his and he doesn't have to touch the volumes at all when he switches beween the two modes. His volume difference is barely noticable. Guess i'm calling my dealer now to set-up a meeting with the local Mesa repair tech.

 

[Jak0lantern01]

I have to do a minor volume compensation on my Deuce when switching to Spongy, I think it's normal since you're dropping the power level.

 

[R_ADKINS80]

Mine is not slight at all.....it cuts around half the overall volume and it doesn't do it all the time. It also loses alot of low end and gain.

 

[boogiemon]

maybe it's just the rectifer tube(s) getting old?

Well, I hooked up my voltmeter to the same wall outlet as my Triple last night and fired it up to play. Sure enough, after about 15 minutes on spongy I got a loss of volume and overall a$$ in my amp. I looked at the voltmeter and it was reading good voltage at 118v. I switched rooms and got the same results. Flipped it back and forth between bold and spongy and and I have to compensate volumes by at least a 1/4 turn to match volumes between the two. Called my buddy up that has a Triple and had him do the same to his and he doesn't have to touch the volumes at all when he switches beween the two modes. His volume difference is barely noticable. Guess i'm calling my dealer now to set-up a meeting with the local Mesa repair tech.

 

[R_ADKINS80]

It does it on silicone diodes as well. I've tried both my 5U4 big bottle and 5U4GB small bottle rectifier tubes and it does the same thing only it's a little worse with the small bottles due to them creating more sag than the big bottle tubes. It's looking to me like my variac circuit is dropping more voltage than it is supposed to when in spongy.

 

[Old BF Shred]

The "variac circuit" is just a tap on the primary of the power transformer. If it had a problem, "bold" would very likely have issues, too.

There is one thing you may want to consider, in case no one mentioned it....
The FX loop in these amps generally uses a "cathode follower" circuit.

Without going into boring detail as to why, Mesa has recommended using their Chinese made tubes only in cathode followers (probably v4 in your amp, and other positions may also be cathode follower, too, usually last gain stage tube).

The issues seem to be exaggerated when using "spongy".

If you haven't yet, be sure these are Chinese made tubes...some of the Russian ones will not work at all or with poor performance. Cheap and easy check compared to paying a tech first off.

Good luck! :wink:

 

[R_ADKINS80]

Thanks for lookin out. I DO have a Chinese tube in the loop slot for that very reason, even though I run in loop-bypass mode. I have another call in to Mesa today and they are supposed to call me back this afternoon. We'll see what hey say. Might just have to drop it off at the local service center.

 

[R_ADKINS80]

Well I had a decent coversation with Rich at Mesa. He's recomending some of the new Slovakian tubes and sending me 3 of them. His first point was most of the new Russians and even some of the Chinese tubes are getting goofy in Cathode follower possitions and wants to rule those out first. I do have 1 JJ here in my stash that i tried in different slots and it seemed to help, so we'll see when I get my new tubes in a week or so.