Single ended Class-A tube wear question

[axemanvr]

I own a Mesa Boogie TA-15 TransAtlantic, which has three power settings, 5 watt single ended Class-A (1 tube), 15 watt Class-A push/pull and 25 watt Class A/B (2 tubes).

I play a lot in the 5 watt power setting and one day I started wondering something...

If I'm running a single tube all the time, then I must be burning that tube more than the other, right? If so, wouldn't this eventually unbalance the power output someday when running both at the same time and should I be switching the power tubes every so often in order to keep them wearing as close to the same rate as possible?

[Jazz P Bass]

I would have to say, yes, the tubes are going to "wear" at different rates.
I would contact Mesa & ask them there opinion.

[axemanvr]

I actually talked to a Mesa Boogie tech about this. He didn't really give me an answer and actually sounded annoyed when I pressed him for a specific answer. His only advice was to tell me that I should just plan to buy a new set of tubes every year. Great advice, coming from a guy who works for a company who sells the exact tubes I need for this amp.

[JoeM]

...should I be switching the power tubes every so often in order to keep them wearing as close to the same rate as possible?

Probably a good idea. Like rotating your tires.

[Enzo]

Give the guy a break. I rather doubt the techs at Mesa are spending time checking tube wear on the various modes. If someone called me up with a tech question and I provided what I thought was my best answer, I might start to get annoyed if someone pressed me because they didn;t like my answer enough.

We don't have the schematic, do we? That would tell us whether you could yank the spare tube or not. (They might share a cathode resistor and it needs to be there, for example.) But that one tube just doesn;t seem like a deal breaker. When I play, I don't stop bending notes to prolong string life. And if I have two amps and one costs $20 less but doesn't sound as good, would I really buy the amp I like less for the $20 difference?

SO your original question was shouldn;t you be rotating their positions? Sure, why not? Takes a couple seconds, can't hurt, and if it doesn't actually help, so what. And if it does help, then you get a couple extra weeks out of the tube. WIn-win.

[redelephant]

No need to rotate anything. Mesa uses a PP output tranny, when selecting SE one tube's grid is simply muted. That way the idle (DC) current thru the tranny is equal for both sides of the PP primary and you don't get saturation from unbalanced current. So both tubes are always in class-A bias.

[axemanvr]

I appreciate your thoughtful answer and I'm not doubting your knowledge of Mesa Boogie amp circuitry, but I have to wonder how it's possible that you know this when Mesa Boogie's own tech didn't seem to have a clue.

I know... I actually don't think he had a clue!

Despite another post defending the Mesa Boogie tech, with all due respect, he didn't actually talk to the guy. I'll give him a break when he can give me a straight answer, one way or another, otherwise he should admit that he just doesn't know.

I find it difficult to believe that I'm the first person in Mesa Boogie's history to wonder if this is a potential issue.

[Tom Phillips]

Ahhh...So you were given some good answers on this forum but you don't believe the advice because even a "Mesa Boogie tech" who "sounded annoyed" at your question didn't give you the answer you wanted?

You could disassemble the amp and trace out the circuit. Then post it here and we will be glad to take a look at it. Otherwise just rotate the power tubes regularly to be sure they wear evenly.

[redelephant]

I appreciate your thoughtful answer and I'm not doubting your knowledge of Mesa Boogie amp circuitry, but I have to wonder how it's possible that you know this when Mesa Boogie's own tech didn't seem to have a clue.

I know... I actually don't think he had a clue!

I find it difficult to believe that I'm the first person in Mesa Boogie's history to wonder if this is a potential issue.

Well, Randall Smith talks about it in an intervue in Guitar Player...Besides, it's a very logical way to do it, no magic or rocket science at all.

Why should the tech know this? He fixes amps, doesnt need to know how every detail in a circuit functions, believe it or not. Most techs are experienced in trouble shooting and repair, but not necessarily E-engineers who understands and designs a circuit from scratch.

[Alex R]

I had a recent Mesa in with this kind of switching, I just forget the model, and that one worked as redelephant says, it muted the grid one side of a push-pull pair. I didn't trace it out, stopped thinking about it once I'd fixed it, but I saw what the switch did to produce the lowest wattage output. There must be something else going on though? Or you'd kind of lose half the wave, wouldn't you?

[Enzo]

Not if the amp is running in class A. Class A means 100% conduction, so no missing portion of waveform.

[MWJB]

..or failing that the amp would just be "single ended, biased closer to cut off than saturation", like the majority of single ended, entry level guitar amps. Even if you are "missing" a bit of the waveform, it doesn't necessarily mean that the amp will sound bad, far from it.

[Jared Purdy]

I appreciate your thoughtful answer and I'm not doubting your knowledge of Mesa Boogie amp circuitry, but I have to wonder how it's possible that you know this when Mesa Boogie's own tech didn't seem to have a clue.

I know... I actually don't think he had a clue!

Despite another post defending the Mesa Boogie tech, with all due respect, he didn't actually talk to the guy. I'll give him a break when he can give me a straight answer, one way or another, otherwise he should admit that he just doesn't know.

I find it difficult to believe that I'm the first person in Mesa Boogie's history to wonder if this is a potential issue.

I was led to believe (by whom I'm not sure), that if you call up Mesa and ask for tech support, you will get, well, "tech support". Here's my experience with Mesa's "tech support".

When I was thinking about buying an LSS, I called them up to ask a couple of questions (which I can't remember at this time), and I was fairly satisfied with the answers that I was given. After relentless testing in a couple of stores in Toronto, I bought one (new) about 6 weeks ago. The amp now has issues, blowing fuses and the Boogie 5y3 rectifier tube left right and centre (2 Mesa Boogie rectifier tubes and four fuses in one week). It now has a Sovtek 5y3 in it, which, as one poster to my thread on this forum pointed out, is military grade, and that is likely why it is not failing.

When I bought the Sovtek, I didn't know that, I just needed a rectifier tube until I could get to another store the next day so as to purchase the warranty mandated Mesa Boogie 5Y3. So when these problems started creeping up, I started freaking out, and called the tech at the shop where I bought it, and he made some suggestions about what to do to test it for certain things, in an attempt to narrow down the range of problems. His suggestions worked, but we still don't know what the problem is, so he has asked me to bring it in, as something is clearly not right, and what might end up happening is the Sovtek could end up frying something in the amp, and then there goes the warranty on a $2000 amp.

After I got off the phone with him, I decided to call Mesa's "tech support" to see if they had any ideas, knowledge, suggestions, etc. A woman answers the phone, I ask for "tech support", she puts me through, and someone answers the phone. "Great", I think to myself, and proceed to explain the unfolding events of my LSS. He did not have one iota of a clue. Zero, zip, zilch. "It couldn't be the amp", he exclamined, "It's just a bad batch of tubes". When I asked him if this was "tech support" that I was speaking with, he said, "Well no, it's customer service, we don't really have tech support". Nuff said.

[Steve Conner]

Sorry, my bad. The Sovtek 5Y3 is not actually "military grade". But it does have a higher current rating and lower voltage drop than a true 5Y3.

5Y3 - Wikipedia, the free encyclopedia

As I said, the warranty isn't a problem if you put one of the Boogie tubes back in before returning it.

[Jared Purdy]

No worries. But being able to use it with the Sovtek does point out that there is an obvious problem with the amp, that is not tube related.