**Smoking integrated tube amp, advice needed:


Hey folks, first time tube amp owner, first time poster here. 

I just received my first tube amplifier - a Mistral MT34 integrated tube amp (35 wpc), and am excited to experience the warm analogue sound that I’ve been saving toward for such a long time. After plugging it into my system, however, it almost immediately started smoking from what looked to be the preamp section/tubes, so I immediately switched it off and disconnected it. The filaments were **glowing** red, and the room filled with electrical smelling smoke.

The component chain looks like this:

Pro-Ject Perspective turntable > Bellari VP129 Phono preamp (100 ohms output impedance) via RCA to the AUX port of > Mistral MT34 integrated amplifier (100k ohms input impedance) > KEF Corelli speakers (8 ohms).

I connected the black side of each speaker cable to the white amp input, and the red side to the red 8 ohm tap of the amplifier.

Is there a catastrophic mismatch between my equipment specs that could have caused me to fry the amp? Have I set it up incorrectly? There’s a new electronic safety test sticker from April 2024 on it as I bought the amp from a charity shop on eBay, so this is throwing me. The description said it was turned on and functioning before the sale, however, so if the seller plugged it into power without connecting to speakers first, could this have damaged the circuitry/caused damage that might have led to this smoking? Would a single blown tube lead to this outcome?

I’m worried I may have fried or permanently damaged the amp, and now face a hefty spend on investigating this with a local AV repair specialist - a cost which I didn’t anticipate, and which has dampened my excitement, honestly. 

I’d also liked to know what caused the issue before I try to integrate it back into my set up and do the same thing again.

Any thoughts or advice appreciated. Thanks so much!

fugazikid1991
Post removed 

return/exchange it.

very unlikely, whatever the cause, don't let this put you off tubes, you just got very unlucky.

oh, bought from a charity shop, then a different story. 

where do you live?

perhaps a member here can help you find a competent repair shop near you so shipping is not needed.

btw, charity shops are not in the business of cheating people, even if they say no refund, I would talk to the manager. After all, it cost the shop zero.

It could have been working fine for the seller but damaged in transit. Boxes get tossed around and could have jarred something lose without damaging the shipping box.  The problem is that if the box itself isn't damaged it can be tough to make a claim against the shipping company.

What I see is a line-up of immature errors usually done by teen that wanted to go for tube amp on the budget and try out some new things.

You really don't want to try tube amps this way when you don't know how tube amp is built and works. As a beginner, your only option is to buy that in person or new in box. Try to return this unit with refund.

 

 

Ayon , machined chassis not sheet metal , Critical for any good tube amps 

Lundahl chokes,and transformers, Mundorf coupling capacitors 

gold copper tube sockets which are much better then most cheap gold brass 

and most important also microprocessor controlled. Most amps average the power tubes output.Ayon monitors and adjusts each tube for wear ,when a tube goes,

a red led comes on and if you are not in the room shuts it down  you just 

replace the tube ,and hit the button to re bias  all the tubes.

in a regular tube amp ,if a tube has runaway voltage and blows ,it can take out a transformer or other parts.made in Austria,not China 

I used to own a pair of ARCs that one or the other would routinely blow a grid resistor, but it was never as bad as what you have described (no smoking and such).  If you are feeling adventurous, unplug it and put it on a work area and pull the bottom off and see if you can identify any smoked electrical components.  Be careful around the capacitors, you might want to get a hold of a shunt to manually make sure they are discharged (although if it has been turned 'off' for a couple of days I would think that they would be).

Someone mentioned "runaway voltage" and I now have a Cary amp and a coupling cap went out and i did get a run away bias going on.  I imagine the tubes got pretty hot in the short time it operated without me catching it, but again:  the tubes were not "glowing red" and no smell of smoke.  If I hadn't have caught it, maybe they would have after a short while, so perhaps you have a run away bias going on, but I don't know anything about bias and preamp tubes and I wouldn't think it would happen "almost imediately."

When you say:

I connected the black side of each speaker cable to the white amp input, and the red side to the red 8 ohm tap of the amplifier.

are those the ONLY four binding posts for speaker cables that are on back of that unit?

 

Your Story is very much in keeping with adice given a long time ago,  in relation to be disciplined towards a safety attitude around tube equipment.

I was informed of Red Valves and the need to have eyes on Tube Equipment at Power On and in use and double check shortly after Power Off.

I am vigilant about this attention given.

You are lucky to have discovered this condition developing, and getting it stopped asap.

The repair is beyond the usual skill set and will need a EE, preferably one that has Valve Experience.  

Other than misusing the term input when you meant output, your setup sounds perfectly all right…assuming the white speaker terminal is labeled negative or 0.  If the amp is set up correctly for your voltage, it was defective.  You should return it.

@fugazikid1991 Sounds like the amp was damaged prior to your placing it in your system. Was the shipping box damaged?

assuming the white speaker terminal is labeled negative or 0

I was wondering about that myself.

I had a Yaquin hybrid integrated that went up in smoke after using it for a couple of hours on day 1.  Back then Yaquin was no well known and trying to get warranty service from China, forget about it.  Return shipping to manufacturer was more than I paid for the amp.  I believe I sold it for under $100.00 as is to a tech guy who told me later he couldn’t get parts for it. You buy crap you get crap. 

Hey everyone, thanks for the help! I think it’s necessary to highlight that I don’t have any ‘in real life’ friends or family who are into this hobby, so I’m very much reliant upon communities such as this to help with my education. I appreciate the anecdotes and insights into your own experiences, mishaps and successes. 

I’m admittedly wet behind the ears when it comes to this, but I exercised as much due diligence as I could in the lead up to this moment, triple/quadruple checking that everything was plugged in correctly and the tubes were well-seated prior to powering the amplifier on - aware as I am of the potential dangers of running tube equipment incorrectly. (I even turn the Bellari off whenever I leave the room, so I’m vigilant in this regard.)

There is no damage to the shipping box, but unfortunately the seller didn’t reply to my request to remove and individually package the tubes prior to posting, so there’s every possibility that something may have been damaged in transit. I’m covered by the 30 day money back guarantee, so I have no concerns there - just a little disappointed, but mainly relieved that the rest of my component chain seems unaffected.

“assuming the white speaker terminal is labeled negative or 0[…]”

  • Correct, the speaker terminal is labeled 0

I’ve learned some interesting tidbits from this thread, but lets also not speculate on the circumstances surrounding, nor the motivation for the purchase (or even my dedication [or perceived lack thereof]to taking this seriously). I also don’t think we should be prescriptive about the ways that people can enjoy this hobby! We all start somewhere, following different paths to get to where we are, making mistakes and picking up vital lessons as we go. That’s the beauty of this for me, and while frustrating, I’m glad for the potential to learn from this. 

All this being said, I really do consider it a privilege to lean into the evident collective expertise of the group here, so sincerely, thank you to everyone for taking the time. I’ll likely take the amp to a local AV specialist for a verdict, as I’ve read only positive reviews of the unit online. Cheers everyone!

@fugazikid1991 exciting times, trying out Tube Gear.  Sounds like a damaged unit and or defective part in the chain.  Doesn’t sound like you did anything at all to cause the issue.  You have a 30 day return option so you should be a good spot to decide if you want to try and figure out the issue, repair the unit or send it back.  
 

It’s cool that you ordered your unit from a Charity Shop, guessing the proceeds will benefit those in need, that’s awesome.  Most of those types of shops aren’t experts in what they are selling, they get such a range of donated items they really can’t be.  Bring that up as they likely plugged the unit in, if it turned on, they figured it was good to go.  Possible they didn’t even hook it up to a set of speakers and since it doesn’t have an old school FM / AM tuner, they would have to also have had a source to hook up, along with speakers. 
 

Looked up your unit as I wasn’t familiar with the it, from a design standpoint, looks to be engineered / built based on proven tube amp design.  If you end up sending it back, give a look to brands that offer a good network of support in the U.S and have features like self bias and a bad tube indicator.  Those features really take the guess work out of Tube gear and some of the maintenance, hassle.  Prima Luna one brand that offers these features but there are plenty of others.  Enjoy the hobby, enjoy what sounds good to you and take some of the comments you’ll see on posts with a grain of salt.  Audiophiles are a strange bread, they can be a little cranky or extremely concocted at times but also can be extremely welcoming, giving of time and really willing to help. 
 

Beat of luck! 

There is no damage to the shipping box, but unfortunately the seller didn’t reply to my request to remove and individually package the tubes prior to posting, so there’s every possibility that something may have been damaged in transit.

@fugazikid1991 If this is the case the elements in the tubes might have gotten bent up and able to short. This could easily lead to smoke!! Bad move on the part of the seller.