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

[JSQT]

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..

I just read the whole thread on the Misho. It sounds amazing!

I am absolutely thrilled with my Backert Labs Rhumba Extreme. I replaced the stock Mullards with a pair of Mazda Ciftes earlier this week and it's really taken the sound to a different level. All of the things I love about the Rhumba Extreme - the space between the notes, the holographic imaging without losing any detail or adding any tube gooey-ness, the powerful bass and airy top end, are enhanced by the Ciftes. It's like giving the Rhumba Extreme a shot of vitamins.

Since the MQ-88uSE issues, I've been listening with the L-509X in bypass mode, and it sounds amazing, BUT nothing like that fully encompassing "sitting in the 3rd row" soundstage that the MQ-88uSE/Rhumba Extreme combo was providing.

I also believe the Rhumba Extreme is a very low gain preamp. I don't have specs handy but it seems like something I read on their website.

The replacement Luxman is scheduled to arrive tomorrow!

 

[JSQT]

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.

Thanks Dan - yes, I really can't explain it. It is hard to believe that a bad tube could take out the resistors like that on an amp as meticulously engineered as the MQ-88uSE. I guess anything in possible, but I am thankful that Luxman did the right thing, no questions asked.

 

[jdandy]

Thanks Dan - yes, I really can't explain it. It is hard to believe that a bad tube could take out the resistors like that on an amp as meticulously engineered as the MQ-88uSE. I guess anything in possible, but I am thankful that Luxman did the right thing, no questions asked.

JSQT.......I agree, Luxman certainly rose to the occasion to make it right for you. That speaks volumes for their commitment to Luxman customers.

 

[aKnyght]

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.

fwiw... does not sound like this was your issue but i will just mention it for reference: last year i ordered a pair of matched 6c33c output tubes for my SET amp, also from viva. similar to your experience, when i installed them there was no amount of bias adjustment that would bring the current down to anything close to an acceptable range. i called viva who sent me another pair... after receiving back the original pair.

turns out that the measurement (not sure what is being measured here) used to match the tubes on the new pair was 91 and the initial pair was something like 120... so, while the initial set was indeed matched they were passing through way too much current.

not sure if this is anything other than coincidence, but my experience is that when these tubes start to diminish in performance the bias also needs to be adjusted down.

in any event, the bias setting of new pair of 6c33c tubes was spot on with all other new pairs i have installed and they have worked flawlessly.

...just something to keep in mind.

 

[JSQT]

fwiw... does not sound like this was your issue but i will just mention it for reference: last year i ordered a pair of matched 6c33c output tubes for my SET amp, also from viva. similar to your experience, when i installed them there was no amount of bias adjustment that would bring the current down to anything close to an acceptable range. i called viva who sent me another pair... after receiving back the original pair.

turns out that the measurement (not sure what is being measured here) used to match the tubes on the new pair was 91 and the initial pair was something like 120... so, while the initial set was indeed matched they were passing through way too much current.

not sure if this is anything other than coincidence, but my experience is that when these tubes start to diminish in performance the bias also needs to be adjusted down.

in any event, the bias setting of new pair of 6c33c tubes was spot on with all other new pairs i have installed and they have worked flawlessly.

...just something to keep in mind.

Interesting... I was considering sending the GLs back to Viva to see if they would swap them out due to this issue. I'm afraid to put them into the new amp in the event they were damaged by the overloaded current. I do know however the problem existed before I put the GLs in, with the flashing out of the Luxman JJs. Kind of a chicken and egg thing, did the JJs cause the overload or was there an issue with the amp to begin with that caused the problem with the tubes. Either way it's impossible to tell if the GLs were okay so I'm probably out of luck on getting a replacement set.

 

[aKnyght]

...Either way it's impossible to tell if the GLs were okay so I'm probably out of luck on getting a replacement set.

might be worth finding someone local with a tube tester to check them out, or even sending them back to viva with a description of the problem and have them check them out... i found viva quite nice and willing to help out.

 

[Shadowfax]

I just read the whole thread on the Misho. It sounds amazing!

I am absolutely thrilled with my Backert Labs Rhumba Extreme. I replaced the stock Mullards with a pair of Mazda Ciftes earlier this week and it's really taken the sound to a different level. All of the things I love about the Rhumba Extreme - the space between the notes, the holographic imaging without losing any detail or adding any tube gooey-ness, the powerful bass and airy top end, are enhanced by the Ciftes. It's like giving the Rhumba Extreme a shot of vitamins.

Since the MQ-88uSE issues, I've been listening with the L-509X in bypass mode, and it sounds amazing, BUT nothing like that fully encompassing "sitting in the 3rd row" soundstage that the MQ-88uSE/Rhumba Extreme combo was providing.

I also believe the Rhumba Extreme is a very low gain preamp. I don't have specs handy but it seems like something I read on their website.

The replacement Luxman is scheduled to arrive tomorrow!

Bob and Andy were both happy to hear this update. I think he said 10db

 

[JSQT]

Bob and Andy were both happy to hear this update. I think he said 10db

Thanks Brian - I did call Andy and give him an update a few weeks ago; great to call a company and have the president of the company pick up the phone.

BTW the replacement MQ-88uSE arrived with no issues whatsoever and the stock JJ KT88s sound amazing. I did pop the GLs in there for a moment and the bias was over 900mv, so I pulled them and swapped the JJs back in. I think the original resistor issue must have cooked those Gold Lions unfortunately.

Everything is sounding gorgeous!

I do think I am going to hold onto the 509X as well. Not getting the response I was hoping for on Audiogon for that thing and it is too precious an integrated to lose for the kind of pricing I'm seeing. I'm thinking I'll run the Monitor Audio Gold 200s from the 509X and use it to power the front 2 channels of the HT and also change things up a bit music-wise when I want a rest from the tubes.

 

[Shadowfax]

Thanks Brian - I did call Andy and give him an update a few weeks ago; great to call a company and have the president of the company pick up the phone.

BTW the replacement MQ-88uSE arrived with no issues whatsoever and the stock JJ KT88s sound amazing. I did pop the GLs in there for a moment and the bias was over 900mv, so I pulled them and swapped the JJs back in. I think the original resistor issue must have cooked those Gold Lions unfortunately.

Everything is sounding gorgeous!

I do think I am going to hold onto the 509X as well. Not getting the response I was hoping for on Audiogon for that thing and it is too precious an integrated to lose for the kind of pricing I'm seeing. I'm thinking I'll run the Monitor Audio Gold 200s from the 509X and use it to power the front 2 channels of the HT and also change things up a bit music-wise when I want a rest from the tubes.

It is really a 3 man operation, Bob, Andy, and Bob's son. Everything is hand built in the back of Bob's house about a mile from me. Some of the circuits in the Pre are patented also. The builds are laid out and assembled beautifully and every pc on the board is straight and perfect. The cases are of decent gauge and the knobs solid and responsive. The Rhythm has a beefier chassis and dual power supplies making it essentially a dual mono design. He had one Rumba Extreme on the bench being custom build with the dual PS.

They use Hegel H20 for Amplification / test and demo. They use Usher Dancer Mini 2s for speakers in the testing/demos.

For Bob, it's all about the Pre Amp and I tend to agree.

Keep us posted.

 

[JSQT]

He had one Rumba Extreme on the bench being custom build with the dual PS.

Now that sounds interesting!

It is really clear the workmanship and attention to detail on these preamps. You can hold the slab of machined aluminum that is the remote and feel the quality!

Funny thing, I recently had a retailer call me on the phone and give me a stern talking to about why I would have spent so much money on something so cheap and simple - the guy was looking online at the time saying "have you even seen the inside of these things??" In fact it was the attention to detail and hand-crafted workmanship that drew me to the brand in the first place (well, apart from their stellar online testimonials). I am sure he'd never even seen one in person, let alone listened to one!

 

[fcdvpds]

Hi JSQT. Just wondering how is your MQ88-uSE performing so far? Are you using a pre-amp or the variable input in the amplifier?
I have purchased the Luxman MQ-88uc in September 2019 (though, only received it in end November). I am using it in a minimalist system with a set of ProAc Tablette 10 signature and MHDT Lab Altantis DAC.

The combo sounds lovely and I like it very much but I am experiencing some kind of issues. I am only using the variable input, adjusting the volume in the amplifier. Suddenly there's no sound from the left channel. I reduce the volume to the minimum and turned it up again and everything went to normal. It only happened three times so far, one in the very beginning and twice last week.
It made me feel a little bit worried.

I checked the bias and everything was fine, v4 measure 450mv and all other very near 480mv.

Any tips of what it could be? My speakers are 10ohms impedance. I was using the 8ohm tap but now changed to the 16ohm just to change something. Sound is very similar, if something different maybe a little bit brighter, not sure.

Appreciate any feedback. Thank you!

 

[fcdvpds]

Hi everyone,

About a year ago I purchased a Luxman MQ-88uC and really like the sound but I have experienced one problem that is distressing me...suddenly there's no sound from the left channel.

In one year of intense use it has now happened four times. I am using a single source connected directly to the Variable input and after turning the volume down and up a few times the sound eventually comes and no more issues for a few months.

Since it works well most of the time and I can't replicate the problem it feels awkward to send it to repair service. On the other hand it is very disappointing that such an expensive amplifier has this kind of issues. I changed the driving tubes (both ECC83 and ECC82) to NOS mullard after experiencing the problem the first three times, I had hopes this could solve the problem but it happened again. I have checked the bias current and all seems fine, reading near 480mV in all tubes.

Has anyone experienced similar issues? Any suggestions would be much appreciated.

Best regards.

 

[fcdvpds]

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

May I know how are you doing with your Luxman amplifier?
I purchased a Luxman mq-88uc in December 2019 and the variable input sometimes fails and there's zero sound from one of the channels. Moving the volume pot up and down a few times eventually fixes the problem for a while but sooner or later in happens again. I am wondering what to do. The last thing I want is to ship it to the repair centre.

Thank you.

 

[stereogeek]

I was really hot for a MQ-88uC a few weeks ago. In my quest for more info on the amp I was told that most of the Mq-88uC's that come in for repair have had different tubes installed than what comes from the factory. No tube rolling recommended by Luxman. I'm sure they sound great with the stock KT88's but I would want to tube roll so it kind of shut me down on this amp. Good luck all.

 

[JSQT]

I was really hot for a MQ-88uC a few weeks ago. In my quest for more info on the amp I was told that most of the Mq-88uC's that come in for repair have had different tubes installed than what comes from the factory. No tube rolling recommended by Luxman. I'm sure they sound great with the stock KT88's but I would want to tube roll so it kind of shut me down on this amp. Good luck all.

Yes I never did use the Gold Lions in the MQ-88uSE after that incident. In fact I came across them in one of my “gear boxes” a few days ago and wondered if/what I should ever do with them. I loved what the MQ-88uSE did that made it special (Luxman tube magic!) but even mono-strapping two of them, they did not drive my 100 dB Voltis very well.

I’m actually close to selling off all of my separates at this point and downsizing to a Technics SU-R1000. It’s on back order until December so I’m currently living with the little brother, the G700MK2. It is a totally unique, different kind of amplifier than any I have heard before. I am hoping (and fairly certain) that the R1000 will blow the G700MK2 out of the water with the additional power and processing capabilities (wondering if their much-touted digital calibration on their phono EQ will beat my JC3+!).

 

[stereogeek]

That's really weird that two of them strapped for mono did not drive those 100db Volti's very well. This little 25wpc Carver is driving the absolute crap out of my Razz's. My room is pretty small but still.... Anyway, good luck in your quest to find the right stuff to go with your Rivals, it can be a confusing journey for sure. Cheers.

 

[JSQT]

Yes, I should have been more clear… there was plenty of power from even a single MQ88uSE, it wasn’t for lack of power into the Rivals, more that there were certain frequencies where there appeared to be impedance dips or something that just wasn’t a good match between speaker and amp where certain upper-mid frequencies could sound distorted and noisy.

 

[stereogeek]

Oh, I see now. The pesky upper mids and lower treble strike once again. That is the area that I am VERY sensitive to any glare or emphasis in that range. I had that glare a few years ago when I moved into my new listening room. I tried everything to get rid of it and nothing would work. I finally bought a new rack and got rid of my solid maple set up with the threaded rods....the glare was gone. Anyway, good luck with your new Technics setup....Cheers.