2. amps-preamps
  3. 189661-190234

**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
pindac's avatar
pindac
2,864 posts
 

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.  

crustycoot
644 posts
 

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.

atmasphere's avatar
atmasphere
11,856 posts
 

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

immatthewj
2,133 posts
 

assuming the white speaker terminal is labeled negative or 0

I was wondering about that myself.

stereo5's avatar
stereo5
6,424 posts
 

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. 

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