New Luxman MQ88-uSE Problems - KT88 is arcing and popping - Any ideas on what caused this?

JSQT

JSQT

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Hey all,

Well, my new MQ88-uSE shipped directly from Luxman 2 weeks ago suddenly started making horrendous cracking and popping noises in the left channel last night.

I swapped sides with all the power tubes and it went away, so I figured maybe one of the left channel tubes wasn't seated properly.

Tonight after listening for about 2 hours, suddenly the same tube (I assume, now in the right channel) started arcing and sparking inside the tube with the same loud crackling coming now from my right speaker.

I have no idea what is happening - being a brand new amp, and moreso being a "SE" with premium matched KT88s, this is extremely frustrating. I've had to shut down my entire system until I can get it sussed out, which I assume at the minimum will be getting new tubes from Luxman, and possibly having to ship it back for repair, after only owning for 2 weeks.

Anyone have any ideas what may be happening here? Could a connection be causing a short? I'm running the output from the Backert Labs Rhumba Extreme directly into the inputs on the Luxman.

Thanks in advance :(
 
Sometimes even new tubes go bad. If you are going to run the amp on a regular basis then you need to have a spare quad of KT-88's anyway and you don't want to wait on a tube to be shipped from Japan anyway. Go to Tube Depot, The Tube Store or even Viva Tubes in Easthampton, Ma. and order a matched quad of Genalex Gold Lion KT-88's. The tubes that come with the amp are just rebranded JJ's. Viva has a matched quad for $175 for the Genalex and $163 for the JJ's. Has nothing to do with the preamp.
 
Thanks, I can grab a quad of KT-88s somewhere and I assume Luxman has some kind of warranty for their "hand matched" special edition tubes that are less than 2 weeks old. Resale would take quite a hit without original Luxman tubes I imagine?

Anyway - a concern is what could be causing it... is it 99% likely it's just a bad tube from Luxman, or could there be a power issue elsewhere in the amp that cause the tube to fail?

Thanks!
 
There is really nothing that can be "special" about the JJ tubes other than how closely they may have matched them. They just buy enough to have their label silk screened on just like Primaluna does with Shuguang. They say right on their website that they are just JJ tubes and after a year having new tubes in place will increase the value. When you get the replacement from Luxman just set them aside and use the Gl's which are a better tube anyway. Yes that is the most likely cause with a new power tube especially from certain brands. If a second one blows out in the same position then you may have a problem but since the problem followed the tube only then it is the tube.
 
Jack said:
There is really nothing that can be "special" about the JJ tubes other than how closely they may have matched them. They just buy enough to have their label silk screened on just like Primaluna does with Shuguang. They say right on their website that they are just JJ tubes and after a year having new tubes in place will increase the value. When you get the replacement from Luxman just set them aside and use the Gl's which are a better tube anyway. Yes that is the most likely cause with a new power tube especially from certain brands. If a second one blows out in the same position then you may have a problem but since the problem followed the tube only then it is the tube.
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Thanks - I wonder if it’s possible to run 120s in place of the 88s. I could pull the Tung Sols from my Rogue while I wait on new JJs from Luxman.
 
Not likely as not shown on the spec sheet or mentioned in description. You are just going to have to break down and buy a set while you wait on Luxman to do anything or you may be down a while. Always have spare power tubes. If that amp has manual biasing you could get away with just buying a pair while you wait to see if they are going to send you a new quad or just one. Actual info on the website is sparse at best.
 
Thanks, just placed an order for the matched quad set of GLs on Viva Tube. In the meantime, I guess it's back to listening to the office system until I get this sorted out.
 
I had a set of the Golden Lion with an ARC a while back. They were nice tubes.

Anything can have a bad one. I had a brand new set of Black Treasures; they were pretty darn expensive. One was arcing right out of the box. It was replaced and the replacement worked just fine afterwards!
 
Thanks guys... my biggest worry was that something may have happened to the amp itself but it sounds like we're all right.

From a tube standpoint, the Gold Lions are delivering next Tuesday and Luxman has ordered another matched pair of 88s from Japan (covered under warranty), which will likely arrive late next week. So I will have the new GLs to demo and a clean set of JJs from Luxman.

Best of all outcomes!
 
Oh - and also a new pair of Mazda Ciftes coming for the Rhumba Extreme next week as well! Lots of rolling will be going on for sure.
 
Interested to see which one you prefer. I also had a bad KT-120 out of quad on new Tung Sols. More common than you think with the new production tubes.
 
As a follow up to this thread... I received the Gold Lion KT88s over the weekend and swapped them out with the Luxman JJs.

Unfortunately, bad news on the amp... When I went to bias the GLs I noticed the tube sockets in V2 and V3 (where I had the bad JJ tube) were getting unbiased current - the meter snapped right into overload status on both tube sockets. No amount of potentiometer adjustment could bring them back in line.

The current line of thinking is that when the JJ went bad, it took out the cathode resistor on the amp as well. So unfortunately this will have to go back to Luxman for warranty repair. It seems like I've been dealing with this tube problem for weeks, and now I guess it will be additional weeks before I get a functional amp back. Disappointing since I have only enjoyed the amp for what seems like 20 minutes or so.
 
I’m so sorry to see the amp is faulty. That’s such a shame.

Is there local Luxman warranty repair?
 
Thanks Joe, yes it is disappointing, especially with the addition of the Backert Labs pre and the M Scaler at the same time. I feel like this new system is never going to come together!

Unfortunately I have no local Luxman dealers. I do have a good tube guy here in town but I am sure he's not an authorized warranty shop. My dealer up in DC (Command Performance) has been great helping me work through the problem over the past week. He's reached out to Luxman to see what the next steps are.

Until then my new Cifte's arrived today for the Backert pre, so it will be fun to imagine what they will sound like through the MQ, LOL.
 
As a happy ending....

Luxman is shipping me a brand-new replacement MQ-88uSE today. Luxman definitely goes above and beyond... great customer service!
 
Huge Congratulations! I love Luxman. That was smart of them to do that.
 
Agree, I was all ready to settle in for a long wait while they shipped it around for service. This is great news. I have been a fan since I picked up my C1010/M2000 combo 2 years ago but this goes the extra mile & confirms my deep affinity for the brand.

By the way, Joe, how do you like the MQ-300? I've wondered how it performs compared to the MQ-88u given its new Mazda Miata-level price point. What preamp are you running into it?
 
JSQT said:
Agree, I was all ready to settle in for a long wait while they shipped it around for service. This is great news. I have been a fan since I picked up my C1010/M2000 combo 2 years ago but this goes the extra mile & confirms my deep affinity for the brand.

By the way, Joe, how do you like the MQ-300? I've wondered how it performs compared to the MQ-88u given its new Mazda Miata-level price point. What preamp are you running into it?
Click to expand...


The MQ-300 is freaking awesome.

Sweet, smooth, round mids, amazing vocals. A great 300B example of an amp.

My main preamp now is the Misho Wooden preamp.

The GAT2, for me, has way too much gain on my Avantgarde Duo..
 
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JSQT.......I am sorry to read about your Luxman amplifier damage. These kinds of events can take the luster off a brand new purchase. At $5,999.00 for the Luxman MQ88-uSE power amplifier, I would have expected Luxman to incorporate some type of power tube monitor system that would have immediately shut down the amp in the event of a power tube failure. That the KT88 was allowed to remain energized, arcing, creating dangerous voltages that damage the bias section of the amplifier seems unacceptable to me.
 
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