Mesa Single Rec Issue

[jak0lantern01]

I bought a single rec combo amp about a year and a half ago and seem to go through tubes a lot more frequently than I would expect. I just replaced tubes a month ago and it's already started to show symptoms of a problem (microphonics especially, but also some buzzing, etc.). The amp had to go into the shop last month due to what I'll refer to a catastrophic breakdown. The guys in the shop told me that a resistor melted out and had to be replaced, probably caused by a failed tube. Well, I have it back one month, and in that time I played one gig and have had practice sessions every weekend. I'm thinking the resistor and tube problems I've had are just a symptom of some other bigger problem. I use the standby switch when not in use. Anyone have any idea as to why I'm going through so many tubes? It's still under electronics warranty. Thanks.

[jak0lantern01]

No takers here on why tubes would be failing on an amp at an accelerated rate? C'mon, someone has to have some thoughts on the issue.

[Ray Ivers]

C'mon, someone has to have some thoughts on the issue.

Oh, absolutely! Could you elaborate on this statement:

I use the standby switch when not in use.

Ray

[TD_Madden]

Which tubes are in-question....from the microphonic standpoint I'd suspect preamp issues, butit would help to know the types of tubes...even manufacturer if possible.

[jak0lantern01]

What I meant was, that when taking a break, I use the switch, so it's not like I'm abusing the tubes or anything. Sorry about the rambling post, the problem is both strange and troubling.

[jak0lantern01]

Mesa tubes (12AX7's and El34's with the correct bias selected). I just replaced the pre-amps for this reason, I couldn't seem to narrow down the source. I've also had to replace power tubes after the amp repeatedly sounding 'dirty' and/or weak. Bandmates notice the problem also. Could this be a power related issue?

[jak0lantern01]

Are we already calling it quits on this one?

[Steve Conner]

If you play real loud with loads of bottom end, your tubes could be getting shaken to an early grave by vibrations from the speaker. Try using an extension cab instead of the internal speaker, and see if they last longer, if so, we found your problem

[jak0lantern01]

I only run the bass at about 50%. After that, we start to get mud. I was testing the amp the other night, just a guitar straight into the amp, no fx or anything, and cranked the master, played nice, or so it seems. Possibly a problem with the FX loop? I usually have FX hooked up.

[Mouthurst]

Try some good quality NOS tubes and see what happens, they should last longer. Or spend the extra coin and buy quality.
Ive got Mullards, Rogers, telefunkins and Sylvanias which have been tortured for years and still going strong and a box of newer used tubes which are NFG.
New tubes are meant to be replaced with built in life spans IMO.
Also if the power tubes are getting lots of vibes put some dampening rings on them it may cut down on the wear and tear.
That amp is probably trying to get as much out of them as it can using "mesa" watts.

Thats what I think
Good luck with it.

[jak0lantern01]

Mesa watts? Dare I even ask?

[Mouthurst]

Originally Posted by jak0lantern01

Mesa watts? Dare I even ask?

Well It was kind of a rumoured joke I heard from a freind because by using advancements in amp design they were squeezing every ounce of power they could from a pair of EL84's. Some thought they were measuring different than the generally accepted methods. Maybe thats shy those amps should use those tubes, tubes gotta be tough to take the designs.

[stokes]

Although its true that Mesa's as well as other high gain amps are tough on tubes there is no reason you cant use other tubes besides Mesa's.They use Russian and Chinese tubes- the only thing "special" about their tubes is that they test and grade them to fit a certain bias range.I have all NOS tubes in my MKIIC+ which both my sons use regularly and the tubes have been in the amp for 2 years now and are still going strong.As Steve said vibrations as well as pushing the amp hard will shorten tube life,but a month is way too short.Since you say it is still under warranty I would suggest taking advantage of that warranty and have the amp checked out.

[jak0lantern01]

I just had major repairs done on the amp. The amp was sounding lousy, really bad, to the point where my clean channel had this really cool slightly overdriven sound going (no I wasn't using the 'pushed' setting'). Anyway, I swapped in some brand new Mesa tubes, and it sounded good again. During practice that night, I noticed after playing a bit that the sound was immediately going downhill again. The next night, I decided to test it out again, this time cranking it up to push the tubes and observe. Essentially, all hell broke loose immediately. The tubes started flashing and the fuse blew before I could reach over to the standby switch. It smelled. Brought it to the shop, it had a good hum even on standby. After the repairs were completed, the techs told me that what appeared to have happened was that a tube went bad at some point and overheated and melted out a resistor. Since the repair, I can still smell the same odor from the night it failed, not as strong and presumably from the incident. The amp has played pretty well since, though, will the exception of some microphonics, which I think I have narrowed down to the FX loop. I've also been alerted that all pre-amp tubes can have issues with microphonics, it doesn't necessarily mean a tube is toast. The pre-amp tubes are only about two months old, at the most.

[Mouthurst]

Ive seen this before-bummer-Sounds like you need a surge protecter-- a small ac surge in the building where youre playing can be a big one in an amps circuit-I use a 5amp one with 4 outlets and a built in reset button-works great.
And yes I have had to reset it a few times.
Worth a shot.

[jak0lantern01]

So you've seen this? That's cool, I figured my amp was just sucking. I'll get right on that surge protector.

[stokes]

You have a 2.5amp fuse in the amp.If you put a 5amp surge protector between the amp and the AC supply your 2.5amp fuse in the amp will blow long before the 5amp surge protector will.A surge protector is to protect from surges in the power supply,this is not the cause of your tubes dying prematurely.If your AC supply rises the DC voltage in your amp rises causing the current to decrease,the real danger is if you decrease the AC supply,say with a variac,then the current draw increases.I am not saying that a surge protector is useless,it just isnt going to help in your case.Look at it this way,vintage amps were designed to run on 110VAC.Todays house voltage is 120 and can be 125VAC in some places.They work fine at todays voltages.If your tubes are dying too soon it is because they are either bad tubes,or something in the amp is causing them to draw too much current.

[jak0lantern01]

Well, that leads back to a question asked earlier: what can be causing the tubes to draw too much current?

[stokes]

The most common cause of power tubes drawing too much current is improper bias.When you say you had a catastophic breakdown and melted a few resistors,I would have to assume you are talking about screen grid resistors,they usually fry when a power tube shorts out,which could be caused from being biased too hot,but that is not the only cause. How hard you push the tubes and how often you use it will determine tube life,but if they are failing within a month,something aint right.Preamp tubes are a different story,when they fail it is usually caused by age,in a case where they fail early it is usually just a bad tube to begin with.Since your amp is still under warranty,have it checked.

[jak0lantern01]

Up until now, I've only been using the Mesa tubes, so bias 'should' not have been an issue. The amp was in the shop last month, so far the power tubes are holding up, so I'm gonna chill on bringing it to the shop for now and see what happens. I do push the tubes a bit, I'll try turning down the gain a bit and see what happens. I've been looking to clean up my sound a bit anyway.

[Alf]

What kind of surge protector do you have ?
I've been thinking about buying one after my TC Electronics M-one died. I suspect from a power surge. The switching powersupply was fried.

Alf

[jak0lantern01]

Welp, the problem has returned. 2 months on the tubes, only moderate playing on the weekends during jam sessions. There's an odor, the amp sounds like shit (tubes are probably near fried), and the back of the amp was almost too hot to hold your hand on. What in the world is going on here? This amp has to get fixed by someone with competence. I really don't have faith in the authorized repair shop that fixed it the first time, they never really fixed it. And there's no way the problem is the tubes, they are jsut a sympton of another bigger problem. I tried to contact a repair shop and Mesa, everyone is closed until January for the Holidays. This always seems to happen right before a gig, and I'm getting sick of my know-it-all bandmates telling me to go to a shitty sounding solid-state on my choice of amps. HELP!

[HTH]

I repaired a mate's Single Recto a few months back - the entire PCB that the output tubes were mounted to was fried. I'm talking about melted and black scorch marks, I'm amazed the amp worked at all in the state it was in.

I removed the PCB and mounted the output tube sockets to the chassis.

The B+ doesn't run too high on those amps so they're not really hard on the tubes - should be good to go with some tested tubes from a reseller you trust.

(EDIT): does this amp have an HT fuse? - somewhere in the back of my mind I seem to remember my mate's Single Recto only had a mains fuse (eek!)

[jak0lantern01]

As far as I know, only a mains fuse. The thing is still under warranty, but its lack of reliability is making both me and Mesa look bad to my 'solid-state' friends. I need to get this thing fixed, and correctly this time.

[HTH]

Is it only me thats concerned about the lack of HT fuse in these amps? - how do they pass safety regulations? (my mate's amp was a US amp that he imported to the UK and ran with a step-down transformer)

I'll have to look next time I'm in a music shop - I'm sure they wouldn't get the CE Certification without a HT fuse in the UK.

Anyone?

[Mars Amp Repair]

Originally Posted by jak0lantern01

Welp, the problem has returned. 2 months on the tubes, only moderate playing on the weekends during jam sessions. There's an odor, the amp sounds like shit (tubes are probably near fried), and the back of the amp was almost too hot to hold your hand on. What in the world is going on here? This amp has to get fixed by someone with competence. I really don't have faith in the authorized repair shop that fixed it the first time, they never really fixed it. And there's no way the problem is the tubes, they are jsut a sympton of another bigger problem. I tried to contact a repair shop and Mesa, everyone is closed until January for the Holidays. This always seems to happen right before a gig, and I'm getting sick of my know-it-all bandmates telling me to go to a shitty sounding solid-state on my choice of amps. HELP!

I'd suggest at this point just getting another set of fresh eyes on the unit...is there any other Mesa warranty servicer in your area? You might call Mesa, as the new shops that are considered phase 1 warranty, will not be listed on their site.
It's not always incompetence, but sometimes one guy can't see what another can sometimes see right away. been there done that...it's the same way with car repair.
Now I know a lot of folks scoff at the idea of only using Mesa's tubes with their amps, but ie; I know I have all kinds of issues trying to get non-Mesa 12AX7's to not be super microphonic & full of hum sometimes, too. esp with JJ's.
It appears Mesa pushes the crap out of those preamp tubes to the max gain, hence the need for those stages to have just the right tube in them. JJ's especially act very weird in the MKII's. (you've seen the chassis tensioning screw in some of those amps I'm sure).
I know your issue is with the output tubes but just on principle, I'd try a different brand than what you're using...why not give the Mesa's a shot.
Also be certain the new shop checks Mesa's records for any possible bulletims that have come out for the amp. It could be going into parasitic oscillation, too.
My 2 cents. glen - Mars Amp Repair

[jak0lantern01]

Parasitic oscillation? That's a new term for me, please elaborate. By the way, I have used the Mesa tubes up until the current set I have been using. Let me ask this, though: could bad or mis-matching pre-amp tubes cause this problem? I find it unlikely, since I've always had matching pre-amps, but I did have to swap a single 12ax7 tube that wasn't a match to the others (all are Mesa, but 4 are Chinese, one Russian, I do believe). I've been told that pre-amp tubes should be interchangeable, to a degree. But I did have this issue long before I mismatched the pre-amps. I do agree, though, about having a different tech look at the amp.

[HTH]

preamp tubes are highly unlikely to cause the problems you've been having.

[jak0lantern01]

I just wanted to pass that variable by the board here, I want to be prepared for when some half-witted amp tech tells me it's the mismatched pre-amp tubes that are causing all of my amp woes.

[Mars Amp Repair]

parasitic oscillation is a fancy way of saying that the oscillation is unwanted & sometimes (esp in power amps) destructive. Ususally takes mods to correct, unless the output tubes are defective & creating the oscillation. Usually occurs around 15-20Khz in audio amps. glen

[Steve Conner]

It's a shame to hear you're having such a nightmare with this thing, jak0lantern I don't know what's wrong with it, but there surely is something wrong with it. Tube amps shouldn't be so unreliable, they should generally just work, and the power tubes should last for a good few hundred hours of playing even if you dime it.

Either bad biasing (causing the tubes to run way too hot) or parasitic oscillation seem like reasonable explanations. Do you see the plates (the large grey metal piece inside the power tubes) glow red hot? Look in a darkened room to see if you can see any redness on the grey metal. This is a sure sign that the tube is being overrun with too much current. Don't confuse it with the heater in the middle of the tube, which is meant to glow.

[jak0lantern01]

I assume the plate is the bottom most part of the tube. I have not noticed any glowing, but there was substantial heat and the sound went to @!#$. Assuming there is too much current, what causes this? I'm beginning to thing that this amp had problems from day one, I've been through way too many tubes over the last two and a half years. I'm getting it into the shop tomorrow (damn, it's starting to sound and feel like my car).

[Enzo]

Several thoughts.

The plate is the metal structure in the center of the tube. More specifically the outside of that structure. if the gray metal looks like it is getting red hot in some spot, that is the overheating we are concerned with. The red spot will usually be right half way up the side of the thing. Think of it as aiming at the rear of the label from inside the tube.

WHy can you say it can't be the tubes? It most certainly can. All it takes is one bad tube, and that can kill the bias to the one next to it. Your amp has worked for a couple months you say. Tubes can come out of the box new and be bad. Or they can fail in two months. Or they can work for 30 years.

I forget, did you mention the brand tube?

And when they fail, they either stop working, they blow fuses, or they do what you describe your amp to be doing. Try a set of tubes you KNOW to be good - even worn ones.

Tubes burn up because they have failed internally, or because the amp is making them conduct too much current. A common reason for this would be a loss of bias. AN intermittant connection from the bias supply to one or more of the tubes would allow them to seem right at one time and not be right another time. Your tech should check current flow through each and every power tube in the amp. He should check the bias voltage to make sure it is there, clean, and up to level. He should also check all the screens for voltage. Screen resistors are often damaged when tubes fail, and a new tube stuffed into that socket won't be working right after that. SO new tubes alone are not always all that is needed.

And the bias voltage itself might not be interrupted, but if the filter cap for the bias is loose, the loss of filtration has the net effect of lowering the bias voltage.

I don't know whether I am correct or not, but I reserve the term parasitic for little temporary oscillations that ride - like parasites - the peaks of waveforms. Little (short) chirps on peaks mostly. I don't call steady oscillation parasitic. In those cases I jusy say the amp is oscillating, or that is has become unstable. In other words, All unwanted oscillations are not termed parasitic in my shop, just the ones that ride the signal waveform.

So, I don't think parasitics would do this to your amp, but steady oscillation could.

[Andy]

Originally Posted by jak0lantern01

...it had a good hum even on standby...

this could be a sign of a bad output transformer. if one half of the primary winding is shorted to ground, and the standby switch is between the plate and screen nodes (no idea if it is or not) you could have some serious hum on standby, and it would probably sound like crap most of the time. not really sure if it would make it go through tubes faster though.

[jak0lantern01]

Perhaps you didn't reveal the entire thread. This has been an ongoing issue. Oh, did you catch the part about the odor coming from the amp and being almost too hot to hold your hand against? I've been going through way too many tubes with this amp, and I baby it. What are the chances that I've purchased so many bad tubes?