**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

@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.

Yes the tubes should have been removed and packed separately you clearly did everything right. I’d just return it and chalk it up to chance and buying used. 

This sounds like a short in the tube connections. The amp itself could be 13 years old if it's a first year model MT34, and so may have been passed around beforehand. 

Stick with tubes! They really pay off and are much less fussy than some here make them out to be. Black Ice Audio, Rogue, LSA, and Cayin are well reviewed inexpensive (a relative term, I know) tube brands.