Life of KT 150 Tubes

I know this is silly. Did you blow a fuse? Are both MB on the same circuit? Maybe one lost a valve (tube) and that affected the other (a surge). I’ve blown tubes that blew the resistors for that valve. That has happened a few times. The rest of the time it was a blown fuse or one going bad from to many hard starts.. That little piece of thermal wire has a BIG responsibility.

I’ve seen 300Bs with 20,000 hours and were close to 100 years old. They had another 20,000 hours left.

1000 hours and 16K+, I’d hand deliver BOTH to the manufacture’s doorstep in Hades before they got away with that one. Serbia here I come.

@vishu 1000hrs is premature.  

Which do you turn ON first, amps or preamp?

Which do you turn OFF first, amps or preamp?

Did you have a power outage/surge recently?

You should buy US-made amps.  Now you know why.

@Helmholtzsoul - Blowing the fuse is my first Guess, and next is blowing the resistor. To check the fuse  unit needs to be opened. Did talk to experienced vale tech, locally, he said he wouldn't even open it without schematics.  I  certainly wouldn't mind driving 300 kms to the only Dealer in Canada. I am sure the dealer would not give me the service Tech info, because I did not buy the unit from him. Auris has  responded they wouldn't give the schematics. 

@Decooney - I Turn Amp OFF first and ON last. No power outrage or surge.Naim separates is on the same circuit. Never used them simultaneously .Alway had bias set between  55mu-60mu as recommended  by Auris. I spoke to Tung-sol they said life is between 1000- 2000 hours. Thats is a big variation!!!!!

@lLoydc -  "You should buy US-made amps". yes, if you are in North America and more so if you are in the US. I would say  before buying check for local authorized center. It is a personal preference that I like European , but comes with a price in North America.  I had issues with Dynaudio during warranty period. canada does not have Dynaudio  distributer  anymore. US distributer were amazingly good to replace a new set of speakers.

The best thing to do is not to wonder why both amplifiers failed at the same time.  The fact is that both amplifiers need repair, and the best approach to that is to fix each amplifier one at a time.  In the process of doing so, it may become obvious why they both failed at the same time, or you may never figure that out.  It makes no difference either way. 

A transformer coupled tube amplifier operates on certain basic rules.  The stress on the output tubes is determined by the plate voltage, the bias voltage, and the current drawn from plate to cathode.  The easiest thing that any good technician can do is to determine those parameters for your amplifiers.  If any of the 3 parameters is way out of specification, then you have a reason why the tube may have blown, and it's easy to fix.  For example, a coupling capacitor between the driver stage and the output tubes may have failed such that there is no bias voltage getting to the grid.  This causes the tube to draw maximum current and burn out rapidly.  Did you notice the tube glowing red instead of typical orange? I admit it is unlikely to lose a coupling capacitor simultaneously in two different amplifiers, but don't assume that both amplifiers failed for the same reason.  For another example, a plate resistor may have failed.  This would also cause excessive current draw, a brief red glow, and tube death.  I don't see why a competent tech won't look at the circuit, even without a schematic, just to test for these easily diagnosed issues and others like it.  If one guy won't look at it, try another.  Also, check on-line for a schematic.  Also, post this on a tube amplifier forum, e.g., TubeDIY Asylum, etc.

@Lewm-  As I mentioned,  I know both units have an issue. It could have been a tube popped, that is ruled out even with new tubes there is no Biasing.  

My issue is I don't  have an authorized tech near me . Spoken to couple of Vale Techs locally  they need schematics before they will open the unit, which Auris will not give. Emailed the distributer and they say take it to nearest dealer. There is only one dealer in Canada. He says "find out the culprit who popped the KT150". at least he could have said bring it over we will get it checked. This dealer did not sell the unit , he became the dealer much after I got the unit from distributor .

I am still waiting for the distributor to contact me.

You do not need an "authorized" technician to sort out this problem.  You need someone who is knowledgeable and has the balls to just do it.

How did you test the KT150’s? I am not saying that they are not damaged and that they did not damage your amp when they blew, BUT the KT150’s need 600 volts on the line to test and very few tube testers can actually supply that.

@vishu  Always had bias set between  55mu-60mu as recommended  by Auris. I spoke to Tung-sol they said life is between 1000- 2000 hours. Thats is a big variation!!!!!

Opinions will vary - and while it may not be related, for reference I run my KT150s at 45-50ma, designer says I can go up to 60ma with no issue yet I have tried them as low as 40ma and they still sound pretty good. Currently running KT120s at 50ma too, good enough, no need to burn out tubes prematurely if you don't need to.   

You'll see manufacturers reporting different life values between 2000-3000hrs for KT150s, and half the for KT120s and yet that can change for the better if you are not running the bias up too much. Ask your amp mfg/builder again on bias too.   

@decooney- I have spoken with the engineer at Auris and he specifically said to adjust bias 55-60 mA.I have tried 45 mA no difference to my ears. Never tried KT 120, engineer Said not to. Thanks for your input

If this is the first and only set of tubes you had, my first instinct would be a faulty production batch from the factory. I wouldn't suspect the amplifiers unless the problem happened with one amp. Moreover, a bias current of 55 to 60mA means the amp is running in Class AB with a B+ voltage around 550V for a 100 watt rated output. At this condition the KT150's are dissipating only 50% of their rated power. This should make the tube last way longer than the 1,000 hour life quoted by Tung Sol.

That said, there are a couple of things a competent tech can do without opening the hood. Power up the amps without the tubes and measure the voltage on pin 5 on each KT150 socket to check the grid voltage. All four grids should have the same voltage within a few hundred millivolts. The pcb pictures of this amp show a time delay to turn on the B+, it is critical -- critical -- that the bias voltage appears on the grid before the B+ turns on and the B+ voltage drops faster than the bias voltage when powered off. Having a substantial voltage on the plate without a bias voltage drives the tube into high current and shortens the tube life considerably.

My suggestion would be to buy a set of tubes from Upscale Audio where they claim to weed out weak factory batches and run the tubes hard prior to sale. 

I guess don't buy nuttin' without schematics. Or from a source you can ship to for service.

From here on.

A schematic is nice to have, but not really necessary for trouble-shooting this particular problem. Basically, if there is nothing amiss with ancillary components (capacitors, resistors, tube sockets, wiring, solder joints), then you have to believe it was tubes. By the way, I forgot to mention tube sockets. Check that all wires soldered to the tube pins on the bottom side are well and firmly making contact. But even that doesn’t always rule out a cold solder joint. Then also, the socket has to have a firm grip on all tube pins. Some of the modern Chinese-made sockets, while they often look really nice, can have a loose grip on tube pins.

You could swap a good tube into a socket where the previous tube blew.  Start the amplifier t up and watch for a red glow.  If it glows red (not orange), shut down the power immediately.  That proves you have a problem in the circuitry.  Sounds like from what others wrote who seem to know these amplifiers, you have a bias current meter on the chassis.  Is that correct? That should be very helpful.

After reading the manufacture state the valves last between 1-2000 hours, I think you have your answer. You were close to the 1000 NOT the 2000 mark. I find that as another minus, but the manufacture published the specs before you bought it, (I hope).

I find that rather disheartening when someone builds ANY power amp that the valves only last 1-2000 hours and are very $$$expensive$$$ valves.

If no one want’s to help, why are YOU afraid to open up YOUR amp?

I’m sorry it happened BUT it’s time to fix the amps. BE BOLD! It could be 5 dollars worth of parts and charging up the electric screwdriver.

I just open up my new (old) Cary SLP-05. I could care less what any manufacture says about warrantee if they put a fuse on the inside. It is there to be changed and it blew for the amps protection, NOT the house or domicile. The home has breakers/fuses for fire protection. The Amp has SELF protection. It has zip to do with fire safety and everything to do with AMP protection.

5 bucks worth of parts and some new valves. I have my fingers crossed for you.

Post some pics after you open them.. Lets get some trouble shooting going on..

I use a 40 watt light bulb, switch, and pigtails with alligator clips. I hook up to the clips to the cap, flip the switch a few time and on to the next cap I want to discharge.

When I first started discharging caps in the house, 30 years ago, my wife came out with a pistol, she actually thought someone had shot into the house. I quickly went to the light bulb discharge method.

Remember Granny Clampett? The Little Misses is close. LOL

In any case OP I wish you well, I'm in a close second with a newer GG MC275. I think I lost a transformer. I've never had a Mac transformer fail, I think this one did. 700-1000 for a transformer. It a the new transformer too. My 1964 MC275 won't break. That is one tough amp..

The OP says that one tube in each amplifier “popped”. That is not the exit mode of tubes that wear out. Normally a tube that is dying due to long use will just begin to sound bad and eventually become impossible to bias properly until the user finally notices a problem and replaces it. Although catastrophic failure does occasionally occur, most commonly at start-up, the amplifier needs to be evaluated.

I appreciate all your input and advise. Some of you seem so technically sound probably you wouldn’t hesitate to open. While I was communicating with you all Manufacturer emailed me back that he will help me out , he cc’d the distributor to find a Tech for me. If nothing happens then I would venture into opening it.Wonder why they make such great amps , market it without having tech support. I have had amps that lasted me for decades.With The Russian war it is so hard to find KT150, it’s solely made in Russia. 2000 hours life is fair. That would last me around 3 years with using my Naim separates . I have opened up Audio Valve from Germany few times. Newer had major issue , changed tubes and fixed point to point soldering. Auris is a beast , hard to open.

All of you have provide me great support and advise. Thank you guys.

@jasonbourne52-   “Forget those new design KT150 tubes! Only use 6550/KT88's. These have proven reliability - and a lot more affordable! JJ in Slovakia makes good ones.”

JJ6650 is 1.6 amps where as KT 150 is 2.3 Amps. I am sure it will work as I am down sizing. But wondering the SQ? Some one suggested KT120? 

It really seems odd that one tube blew on each monoblock at the same time. Assuming the tubes are wired in series, was it the same tube that blew on both?

JD

It isnt possible to determine tube life without the specifics of each application. As another points out, this tube is very difficult to test properly on any "suitcase" tester of which I am aware. To test properly you would need a custom rig. 1 to 2 thousand hours is a very short life span for power tubes. But considering that this tube is new production only, this just may the price you pay for no old stock variant. Some of my guitar amp clients claim that old stock Mullards are giving them over 10 years, while new production tubes last around a year. 

I dont think substitution of type is the answer. 

Output tubes are usually wired in parallel, not in series.  Thus it is quite possible for one to fail while the others roll along. I have no idea why my previous post was deleted, but it was. Perhaps an overzealous censor.

 The only tube tester I am aware of that has any chance of properly testing a KT150 is the Amplitrex AT 1000.

As you guys seem so knowledgeable . Let me tell you this.

When I turned on my pre and monos , left Chanel was not working , checked the input and out , everything was good. I did get a faint burnt smell on the left unit. Left unit had signal coming in. Right unit was working. I changed  both the KT 150 from left to Right , I couldn’t tell which tube popped, that’s it even the right unit stopped working. Both units had signal coming in. But no sound.  

Quote: "“Forget those new design KT150 tubes! Only use 6550/KT88’s. These have proven reliability - and a lot more affordable! JJ in Slovakia makes good ones.”

That might have been true 4-5 years ago. Not so much any more. Its possible OP got hands on some early gen old stock 150s with the amp from 4+ years ago. Just a hunch. They had gotten it sorted out past few years. Again - buying tubes from a reputable tube dealer/reseller matters. Buy from someone with proper test equipment who actually stress tests, listens for noise, and matches output tubes before sending them out. Now fast-forward there are other sourcing problems of course. Hoping at least 1-2 other new builders step up with even better KT120, KT150, KT170 gen tubes. They could sell the crap out of them if they did it right. .

@vishu I had a Jolida 3502p Amplifier and immediately installed cryo’d by Upscale Audio in L.A. 4x KT150’s and they were fine for 8 months. I sold the Amp only to finance the hand building of 6 Orchard Audio Amplifier modules.

The current owner has had the Amplifier since Aug. of 2021 with no issues.

I had Tubes Cryogenically frozen when I bought them from Upscale only because I read somewhere that they will last longer. Nothing to do with how they sound.

Not much help advising you but that was my experience.

Hi Vishu. In your original post you mentioned both tubes went bad at the same time but in your last post you mention the left amp going bad and the right amp was still working. After switching tubes from the bad left amp to the working right amp, the right amp then blew.

My guess would be that possibly a bad tube blew an internal fuse or resistor in the left amp, rendering it inoperable. After putting the suspect left tubes into the right amp, it caused the same issue - a blown internal fuse or resistor. Thats just my guess. 

I just looked for pics of the internals online. The only ones I found of the circuit board do not show any fuses but I'm not 100% sure these pics are the same as your amp. I'm hopeful that even if it is a resistor rather than a fuse, it will be easy for a competent tech to find a cooked resistor. Sounds like you are on the right road since the distributor has been asked to find a tech for you by the manufacturer.

These days, I don't buy anything without thinking about what I'm going to do if it breaks. There are so many boutique, one man operations and foreign manufacturers that it is easy to get stuck on an island with a faulty piece of gear.  I hope you have a quick, successful resolution of your issue!

The Amplitrex is not going to give a KT150 an adequate test. Better than most other older testers but still it doesnt have the juice. 

Very few tube sellers are willing to test these higher voltage tube correctly as it requires a much higher than normal investment. I checked into a custom made rig and when I finally found a competent builder that was willing the price was just too high for a tube which is more of a commodity and can always be found cheaper than what I would have to charge.

Not necessarily. The Amplitrex can supply 500 volts on the line, which as you say is not ideal, but it is the best out there. This would give one a better idea about the general health of the tube than any other tester i am aware of. Are you aware of a tester that can supply 600 volts? Custom made is probably not the answer for the reasons you state. 

Vishu,

 Where are you located?

I'm not sure why Motet would send you out to Edmonton. I do a lot of work for them, including all they're tube work.

Send me an email, we can discuss..

Hello Vishnu.  The life of a tube depends on how hard it it driven. You mentioned that the other tubes tested weak. That means they were were working very hard. Does the amp have a power rating areound 100 watts or more? That's really pushing any pair of tubes. If it's only 50 - 60 watts, that's reasonable for those tubes. If the voltage supplied to the tubes is not over 400 volts, you could probablsy use 6550s or KT120s and live with a lower power output. If you can set the bias  make it about 3/4 of what the original tubes called for. It should sound OK. If the voltage is over 400v (I'm guessing it is), look up the tube specks for whatever you replace them with. If they can take the voltage, try an easier to find tube. Remember, 100 watts is not twice as loud as 50W. It's only 3 db or so louder, hardly noticable. 100 watts sounds about three times as oud as 10 watts. That's the reason so many people are happy with 300B tube amps than don't even make it to ten watts (they can do more but sound rather bad). I wish you success. This is not a good time to need tubes.

What an absolutely STUPID statement by @lloydc 

I have over 3500 hours on KT 150 tubes in my X200 by Audio Hungary (stupid)  

You should buy US-made amps.  Now you know why.

Faint burnt smell means something inside the amp went bad, probably a resistor burnt up.  That could be caused by a tube going bad.  Moving the bad tube to the other amp would then cause the other amp to go bad.  I never do the switch tube around test for power tubes because that can damage the other amp (or channel in a stereo amp).  It is far better, when something goes wrong with a tube amp, to first have the tubes tested.  

The sort of good news is that is that the most common failure-a resistor going bad-should be relatively easy to fix by a competent technician, even if the technician doesn't have the schematic.  Perhaps you could persuade the technician to have a go even without the schematic.

Are you sure that the Amplitrex can supply 500? I thought it only had 400. I am going to check this it out and if you are correct this may be a solution which would necessitate buying an Amplitrex for power tubes. I compared the Amplitrex with my Triplett 3444 and the similarity of results were very surprising on 9 pins and many octals. What I didnt like about the Amplitrex was the amount of time required to test.

The Amplitrex is so easy to use and it does not require much time at all to use.  It has a warm up cycle that is timed for the particular tube being tested so that the tube would be measured when reasonably warmed up.  I would not want a tesster to be "fast" if that means measuring before the tube has been warmed up.

@boomerbillon - where do you draw the line for 'Driving the amp Hard'.  I am following the instruction as per manual and the engineer to specifically have the mU between 55-60, driving 8 ohms focal Sopra 3 speaker. My volume is never past 25-30% on my pre amp Audio Valve Eclipse. Your advise is appreciated.  I will try 6550 and experience the difference.

A local dealer that exclusive deals in tube equipment often sees repeated early tube failure and the kind of failure described here where there is also damage to the amp from the same customers while other customers running the same model of amp do not have such problems.  Most often it is from excessive voltage coming into the customer's home.  He has equipped those customers with voltage regulation to drop the voltage to some more reasonable level.

+1 @larryi agree, and most don't even realize they've had a voltage spike occur until one of the components isn't working and start troubleshooting backwards from there.  

@audition__audio If you check the specs of the Amplitrex it states it can supply 500 volts on the line.Like I said, it is the only tester I know of that can actually test the KT150's.

I agree with above, having owned tube gear since I was a little kid. I think you had tubes made on a Monday morning or Friday after lunch : )

It is a bit more than strange that Both amps died EXACTLY at the same time...

Hope you can get back on the road soon. Being without good sound sucks!!

All the best

grossman616,

I think the original poster explained that after one channel failed, he moved the tubes to the other monobloc amp and suffered the same failure. This means a bad tube in the first amp.  Whether or not that amps themselves are damaged is not clear, because he did not report trying the good set of tubes in either amp.  In any case, this is a good example for the practice of NOT swapping tubes when an amp goes down--you could be exporting damage to the other amp or channel if the tube failure is also causing damage.  The original poster also mentioned a faint burnt smell which pretty much rules out the failure being limited to the tubes themselves.  That smell means that, at the very least, a resistor blew (common mode of failure, my friend says cathode resistors also act as fuses, and does not consider that failure to be much more of a bother than changing fuses).

@Larryi - Lesson Learnt well, unlike Tube preamp which is self biasing , I agree that swapping popped tubes could have damaged my Other Amp. 

It could be a blown fuse or a resistor, but damn this unit requires an experienced tech to even open it. unlike other tube amps I have seen, this unit is almost concealed. The Auris company in Serbia gave me " fantastic solution" take it to their service center in California, while I live in Canada. Upon calling the service center he said it would be cheaper for him to fly to Canada, as both units crated weigh almost  100Kgs. Canadian distributor spoke to me and asked me to take it to Edmonton 300 Kms away to their dealer. I am going this morning and will keep you all  posted. I once again appreciate all you guys for your input and advise.

How do I post pictures?

@vishu

Really heart breaking story. That is a huge investment… in what should be a trouble free set of amps. Sorry to hear it.

Road trip?

I worked for a Japanese company for a long time. Our office was in Vancouver Washington. Sometimes some of the Japanese would fly into New York and think they were going to take a few days off and drive from New York and see America on the way to Vancouver.. This lasted as far as Pittsburgh usually… one group made it as far as Chicago.

I lived in Edinburg Scotland for a year. When first there I asked a colleague where he lived and he said on the other side of the country in Glasgow. I was aghast, I asked, “do you have an apartment here?” No, I drive… it is 45 minutes.

I lived in Tokyo for a year. Most of my colleagues commuted 2.5 hours to work and 2.5 hours back. I ended up managing two teams there… both in Tokyo… it was a 2 1/2 hour commute each way every day… by train… frequently smashed at 2AM after a business diner.

It is all relative.

I am a novice and know nothing about this (hasn’t stopped me before), but I have an idea.  As several members commenting here seem to know a lot about testing electronics, including tubes, perhaps one or more of them could offer to check out OP’s unit and see what they find?  I don’t know OP’s skills, but if it were me I would be in the dark and welcome ANY knowledgeable help.  Maybe arrange a time for OP to drive down with units and get a chance to hear the helper’s system while the units get checked?  Maybe some local sights to see.  Preferably not involving a real long drive?  (I’m a Buckeye but admit that there are some very smart, knowledgeable Michiganders (or Washingtonians, New Yorkers) that might help in a situation like this).  Just an idea.  Good luck to OP. 

I hope all goes well on your road trip to the dealer.  The good thing about tube gear is that pretty much everything is repairable, and because the circuit is relatively simple, the cost should not be very high.  The exception would be something that damages the output transformers (very unlikely) or the power transformer (more likely, but still not that likely--the fuse should prevent that outcome).  I don't know if the dealer can do a while you are there kind of repair; let's hope that is the case and you don't have to have the amps shipped or you don't need a return road trip.

@ jerryg123.  You've been lucky.  Isn't that nice.  Why comment on something you know nothing about, much less hurl a pointless ad hominem attack? 

You obviously have never had to ship a 100 pound amp back to the manufacturer for repair.  It costs about $200 to either coast, each way, from where I live.  It costs considerably more if you do not have the original box or do not wish to lift and pack it yourself; recently it was c. $360 by Freighters and Craters, one way.  I do not intend to ever ship an amp to Europe or China, but I do plan to keep supporting US manufacturers.   

@vishu ...asked me to take it to Edmonton 300 Kms away to their dealer. I am going this morning and will keep you all  posted.

How was the trip to the dealer in Edmonton back on 4/17 - were they of any help, any luck? Curios to learn more about what compromised your KT150s. Thx.