Audio Research REF 750 pre July 4 FIRE WORKS. TUBE ARC.

Hard to read. Good luck.

This is a not uncommon type of tube failure in ARC amps and yes, it often takes a sacrificial resistor with it.

I once had a similar experience with a large tube amp. It certainly makes your heart rate spike! These days, I think a tube amp with a minimum number of power tubes is the answer. Otherwise, ss is a very good option.IMHO.

Sorry to hear about your problem. It is really terrible to happen before holiday after receiving your updated preamp.

I would say this is a very uncommon problem that only very occasionally happens to tube amps. It almost never happened with preamps because the tubes are much lower power.

A friend of mine bought a Rogue tube amp twenty years ago, this happened shortly after he received it. He replaced resistor and tube, never having a problem again. I know many folks with tube amps and am friends with a dealer who have never had this happen in his broad experience.

So, yes it very occasionally happens, I doubt very much it happens more often with  ARC, it is caused by a tube failure and is possible with most tube amps.

Tube amplification is very popular because of its sound quality.

I have an audio research VSI 60.  It burns through tubes very fast, and has to be repaired every time.  I don’t agree this is a tube amp issue. This is an Audio Research design flaw/issue.  
 

My Primaluna doesn’t even blow a fuse when a tube goes out, and tubes last way longer.  Too many people rush to defend Audio Research.  
 

I've had ARC amps for 30 years and this happens.  I have some of the resistors around someplace, hopefully.

It is the reason I would never leave home with the amps on though and usually want to be in the room with them.  your tube cost is going to be $3-4/hour, so don't leave them on if you are not listening.

This is not uncommon. I had a pair of ARC Ref600s, predecessor to the Ref750, and this happened every once in a while. The fireballs can be quite harrowing, but getting the amp fixed was always pretty easy: just replace the resistor and the tube. 

So, my take on this might deviate slightly from what has been contributed so far. I have owned many Audio Research amplifiers over the years. On two occasions, with two separate amplifiers (D70MKII and VS110); the same pyrotechnics you experienced took place. Both occasions sacrificed components (resistors) in circuit and required a trip to Audio Research for repair.

On both occasions I was living in a costal community, in a home without air conditioning and it was summer. Neither one of these amplifiers could possibly put out the heat of your Ref750 amplifiers. One key takeaway for me; if you’re using an Audio Research vacuum tube amplifier(s), make darn sure the listening room is plenty cool.

Currently enjoying a VSI75 in an air-conditioned environment…

@tubegb  Wow yes u are so right the fist thing I noticed was like how much heat these 750s put out. It was like having 2 big heaters on high with them. I heard they would be putting out some heat but they really blow some high heat. Lol. I thought my Krell FPB 600 put out some heat lol. Also yes I definitely have AC in my listening room. I would definitely would not be able to stay in there without one especially with the REF 750s. In the winter it will be nice as I don’t get the best heat upstairs in my listening room. 

Thank you all who responded. My ARC dealer in NJ contacted me this morning. John Rutan from Audio Connection in Verona NJ. Even before I had the chance for his store to open and call him first. He read my post and called me as soon as he read what happened. He also explained how and why this could happen. And said to call ARC and order the V10 K150 and some extra resistors also to have on hand. As soon as I get them delivered from ARC to call him and he will have his Service tech come to my home and repair what has to be with the REF 750. And basically said it’s not a big deal that this does happen ever so often with a bad tube. Hopefully it wouldn’t ever happen again but I am grateful that I don’t have to send it back to ARC for repair. I have known John Rutan since I bought my first amp and preamp from him in 1991. It was a Counterpoint SA 220 amp and an SA 2000 pre. He is such an awesome guy and SO very knowledgeable. He really left me feeling so happy and positive about what happened last night. Thank you so very much John !!!! 

24 KT150's per amp! Yikes! Bet your electric bill will be going up!

@tattooedtrackman 

now you are officially, and finally, a fully recognized member of the audio research tube amp owners’ society

welcome!!!! enjoy the music!!! 😁🤣

The 4th of July came early for you.

@jjss49 Yep I finally made it !!! 😂 

@jasonbourne71 That’s ok. For this kinda sound it’s definitely worth it. 👍

I have 3 tube integrated amps none an ARC so I am just curious what is particularly different about a KT150 tube in your amp's V10 position vs any other KT150?

My apologies. LoL! I have to laugh at the timing of you tube arc fireworks!

I recently took on a job myself, repairing my single ended triode amp. I heard a pop, splurt and puff of acrid smoke accompanied by the smell of burning cap. Opening the bottom plate, i located the failed part. Not sure if the wirewound Dale / Vishay RH-25 25w 220ohm resistor had gone too, i decided to replace also. The cap was a Philips HP LL 330ohm electrolytic cap. These older caps at exact value are hard to find. I eventually located both and soldered them in. Worked great. Then the opposite side gave out in the same manner. Fortunately i had ordered multiple replacements. I also picked up a quad of nos Mullard (Blackburn factory X3) EL34, along with an old and fantastic nos RCA 5V4G rectifier. A ‘potato masher’ Ratheon had been put in by someone so i just returned the unit to correct spec. Sound is much MUCH improved. Fingers crossed no more fireworks : )

I can't imagine a life where I can't do my own repairs.  I blew a resistor a couple monts ago.  went to my shop and didn't have the right value.  Ordered it from amazon and was listening to music less than 24 hours later without a single post on the internet.  

I know I'm the exception but think others should consider being a bit more self sufficient.

Jerry

John Rutan  (Audio Connection) really does care about customer service. a great dealer 

@tattooedtrackman along with amp tubes, keep an eye on the power tubes in your Ref 6SE. Check with ARC on their lifespan and drop in a fresh set ahead of time. Signal tubes will live longer and die more gracefully do nothing much to be concerned about there. 

Yes, I had similar happen in 2010. I know it sucks. It was an EH KT90 in one of my Rogue Apollo monoblocks. They're no lightweights at six KT88/90/120 per side, but still nothing like your 750! Anyways, yeah a few seconds of fireworks and then a pillar of smoke. No big BANG, fortunately.

The tube (presumably it shorted out) and its resistor (a big blue metal oxide one) were toast. It also singled the board under the resistor, stripping the green mask off and exposing 1cm of bright copper trace. It would've been OK to just replace the resistor and tube, but since the amp was only a few months old at that point, I sent it in and got the full audio board replaced. It didn't put me off tubes - sh*t happens. I swapped to KT120 shortly after this incident. 13 years later and I've never had another tube incident. 

@gpgr4blu  💯.    @audphile1  I definitely will 👍. @mulveling  I totally understand that s””it happens. But the first 3 hrs or so of listening to them for the first time. Wow what a thing to happen. And I’m definitely a virgin to tube amps . And wow what a way to find out about tube arching with a REF 750 KT150. 😂

The similar thing happened to my ARC VT130.  I posted about the solution here: 

https://forum.audiogon.com/discussions/mystery-of-red-plating

I'm sorry for your loss. I know you have wanted that Ref system running for a long time now. 

Did you check to see how many hours the tubes had on them before you fired up your amp? Did you ask the previous owner if the tubes were original (ALL of them) or had been replaced and if replaced, from where were they sourced?

KT 150's are problematic. They are great when they are great but the QC coming out of the New Sensor factory is terrible. Few middlemen can supply reliable matched sets of them.

I apologize for being critical, but will say that as an owner of four ARC amps past and present (present are the Ref 150 SE and Ref 80S), I would have warned you that the Ref 750SE's are NOT the amps to start out with as your very first tube amps. Add the fact that they are used and your choice is even more unfortunate. The more power tubes you have, the more likely one will arc and fail. Add KT150's to the mix and well, this was not unforeseeable. 

I would have taken your amps to John Rutan to check out before you fired them up for the first time. If you had done this, there is a good chance (but not necessarily) that John would have seen something amiss with bias. This concerns me; "Tube bias is controlled by two KT150 tubes, each driving a bank of eight KT150 output tubes" (from the website). With my Ref 150 SE there are four KT 150's per side but there are two bias pots per side so that one KT 150 is "slaved" to the other. When an output tube is failing or faulty, it can most often be detected by checking bias on my Ref 150 SE. Perhaps with your Ref 750 SE's the best way to check all those tubes is to pull them and test them on a good tube tester. 

What you evidently did by unboxing them and firing them up right away is perform a stress test and the stress test failed. I am not trying to beat you up over this, nor should you beat yourself up about it-it is a good learning lesson. 

I truly hope John can guide you on the path of getting reliable service with 32 KT 150's running in those monsters. 

@yesiam_a_pirate   Wow. That’s awesome to hear that u found a great local tech and what a great price. I am very grateful to have my ARC dealer  and friend and extremely knowledgeable I have known for 30 yrs John Rutan from Audio Connection in Verona NJ. 

@fsonicsmith1 No need to apologize for being critical. I appreciate it. U made some very good points and the tubes had 660 hrs on them. All the tubes were purchased from ARC matched set. I even bought a brand new 2nd matched set from him that he also purchased from ARC. I would never buy these tubes from a middle man. I would rather pay 💰 a lot more for them from ARC knowing they will be the best out there and matched. 1 thing I did not do when they were warmed up for about an hour was check the bias on them. I did ask my seller if I needed to and he told me he checked everything out completely right before he shipped and said they should be totally fine. I also went by the meter that showed they were in normal operating range. I ordered the new KT150 with the exact number written on the tube from ARC and also new fuse and extra resistors. When John Rutan and his service tech comes to my home to do the work I will have him check everything out with them and see if they can check the tubes out and bring a tube tester also. The amps were bought from a member from here and I have spoke to him and texted each other for hours and he is extremely knowledgeable about these Ref 750s and explained everything I had questions about and many more that he brought up. Any questions I had he was always there for me. As a matter of fact he was the first person I contacted when this happened. And he was the first one who said it’s not a big issue. And told me exactly what to do and what to look for about the arching. And said it definitely does not need to be shipped to ARC for repair. As a matter of fact he boxed up all the tubes and made sure to number them and put them all back in there exact valve socket locations. And also told me to make sure there were all securely pushed down in place. I really don’t think there was nothing that he left out for me to do and explained everything I really needed to know and more. We also became friends and text all the time I know he will always be there for me also with any questions or concerns I may have. I even sent him my Straightwire Crescendo quad wired for my B&W Matrix 800s as they were Bi wired for my Krell FPB 600. He reterminated them for me. Changed and soldered the spades to Cardas to the exact size I needed for the binding posts on the REF 750s. Beautifully shrink wrapped the ends. .Custom made beautiful oak blocks that he mounted them too about a foot where they get connected to the 750s. BTW he is amd works as an audio engineer. 

Bringing a tube tester for KT150’s can be an interesting idea. Problem is they require 600 volts at the plate, which almost no tester can deliver! Also, it is a good thing you live in a colder climate, because, as you mentioned the Ref 750’s can do double duty as a space heater if needed!

Not trying to be negative here either (like other posters have also mentioned), but I sometimes wonder where ARC come up with these designs???

Not trying to be negative here either (like other posters have also mentioned), but I sometimes wonder where ARC come up with these designs???

There has been a lot of negativity towards ARC for years on this Board, long before it's recent troubles, and as an ARC fan I have little trouble ignoring the naysayers. All that said, on this I agree. I bought my first ARC amp, a VS110 from what I gathered was a very wealthy and knowledgeable guy who had a collection of ARC amps. Years later after buying the VS110 from him I contacted him to say hello and he mentioned he had another ARC amp to sell. I lost the email and can't remember the model name/number but what I will never forget is looking it up and it looked like a welding machine. It was similarly vertical to the Ref 750 but far more industrial looking. Those of us that follow ARC closely recall some real duds, regardless of looks, in the VT range. They were almost universally panned sound-wise. They also were very difficult to bias without being an expert. 

I do wish ARC would not mount tube sockets directly to circuit boards. The implementation, finally, of fuses on the tubes as in my Ref 80S is welcome. 

VAC and others have built and sold monster tube amps with vertical designs but power is useless without reliability and user-serviceability. 

VAC and others have built and sold monster tube amps with vertical designs but power is useless without reliability and user-serviceability.

Even the biggest VACs still use only 8 output tubes per side, compared to 16 in each Ref 750! At that point IMO you really need smart audio-bias circuitry to continually monitor & regulate the bias of each tube and shut down problem tubes (hopefully) before they spiral into a smoke show. VAC went that way starting with their "iQ" series. I have 200iQ and Master 300iQ now, and trust them implicitly. I believe ARC also started using their own version in Ref 160 series. But the Ref 750...yeah that’s gonna be a tough one to keep running. The fuses in my Rogue Apollos did NOTHING to prevent the KT90 arc/short problem.

I have also heard warnings about KT150 tubes. I would definitely move into KT120 or KT88. You need extremely reliable output tubes if you’re running 32 of them.

@mulveling You are one of the most knowledgeable regulars on this Board. When you post, particularly in the analogue section, I read what you have to say. I appreciate your input here. 

Just catching up on my Agon reading. 😀

@tattooedtrackman I’m sorry to hear about your experience! That had to have been a shock! I’m not writing about the amp situation however. 

You said you have a pair of B&W Matrix 800s. As rare as they are I’d love to talk with you about them. My pop’s (RIP) are in storage pending our next home.

Good luck with the Ref 750s!

Happy listening.

@musicfan2349  I would enjoy talking to u about the B&W Matrix 800s. 👍

@fsonicsmith1 I believe the ones u were referring to were the 600s. 

@tattooedtrackman I’ll DM you sir!

@musicfan2349 Awesome 👍👌

Inasmuch as the OP's situation has been addressed, and a fine example of Audiogon community support I would like to add, what stands out to me is why and how John Rutan has so distinguished himself! Stories of John's praise have appeared here for years - it takes time to establish such a legendary reputation. - I don't think that is too strong a characterization. He stands as a defiant answer to the many Audiogon threads about reasons for the demise of so many dealers. His perfect response, even before the "doors were opened", assuaged the OP and enacts a plan of action to solve the problem. Well done John, and a notable example of a key element of success! *

* Though not a customer, I have spoken with Mr. Rutan and found him to be very helpful, as well as knowledgeable.

@truman   Thank u so much for that terrific response about Mr John Rutan. I have known him from 1991 from my first purchase from him. At that time there were many brick and mortar hi end audio stores around in the tri state area where I am from NY NJ PA. I’ve been around to many of them but there was no one like John. He has always been there for me on many buying experiences, demoing equipment in my home ,servicing equipment , making me custom speaker cables, knowledge , patience, kindness and any questions I ever had in those 32 years. Always has been there for me and I know that he is there for anyone that has questions or needs help with anything audio related. A true stand up guy. A great asset to the audio community. I am very lucky to have gotten to know him for that 32 years and counting. 

This shows why this company just went bankrupt have heard similar stories about McIntosh

@rbyington711 

I don't know where you heard that about McIntosh, but it is not true. You may or may not like the sound of their gear, but it is reliable.

What I was referring to in this case were situations where people had sent their equipment into Mac for repair and they get it back and it malfunctions again right away. This is what happened to this individual with ARC nothing to do with the sound of Mac and if I like the sound. I look forward to your response 

@rbyington711 

I made it clear that it had nothing to do with how they sound. I said that from my own experience, and the related experience of others here and elsewhere, their equipment is usually very reliable.

I guess you have never heard that there are brands of gear that have over the years with great reputations that are putting cheaper and cheaper parts into their units but yet the prices don't reflect this. Additionally, people here on this forum have stated they have sent there Mac in for repair and when it comes back depending on who benched it with more problems than before it's sent in. How much research have you done on these topics?

It's like SLR cameras in the 1970 and 1980 Cannon us to build their products like Tanks example the FTb N years later you would pick up a one of their camera an unless it was an F1 most parts that used to be steel where no spray painted plastic

Of course I have heard such stories, as well as having experienced it with some products, but I have not experienced this with McIntosh, nor have I read a significant number of complaints about their reliability or service, and I have been here for a very long time.

Sorry to hear about your trouble.  I had a REF 5se that had problems with the mute function (sound bleeding through the right channel) and also blew the 6550 in the power supply.  That took out a a good bit of the board around that tube.  This was when the pandemic was starting to wind down, so ARC wasn't accepting out-of-warranty units for repair.  ARC recommended that Ben Jacoby in Brooklyn repair it.  Ben has an excellent reputation.  Bottom line is that he repaired the damaged board, but couldn't ultimately get the mute function to work properly.  Also, the preamp always sounded too bright.  I ended up selling it to a mutual friend at a fire-sale price.  My REF 75se, by the way, is working and sounds great.🤞🤞