2. analog
  3. 176347-79353

Life of KT 150 Tubes

Auris audio Mono Block -Forte 150 uses Two KT150 for power output for each monos, Very strangely a both amps popped the KT 150 same time. I can vouch it had less than 1000 hours in 2 years as I have NAIM NAC 252/NAP 300 in the same room. I tested the tubes and one is 100% dead and the rest have very marginal life. With great difficulty I have ordered four new tubes. Would any of you know why this would have happened, in the sense bath amps not working at the same time? I am trying to get hold of Auris in Serbia. Even a good Valve tech will not open the unit without schematics and Auris wouldn’t provide one. I am in Canada. There are 2 authorized service center in the US. When crated both amp weighs 94 Kgs.Not easy to ship. I tried with a borrowed set of TUBES , there is no Biasing at all,mA reads 0, but there is signal coming in and VU display lights up. 

Lesson learnt well not to buy equipment that is hard to service. I bought this even before there was a dealer in canada. I tried contacting the distributor Motet in Toronto. They are telling me to contact Dealer in Edmonton 300Km away. He never sold me the unit, why would he have any interest if he didn’t make any money on this unit? The unit cost $16,800 USD. Any advise what I should do?

128x128vishu
vishu's avatar
vishu OP
28 posts
 

@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.

lewm
13,080 posts
 

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.

daveyf's avatar
daveyf
2,871 posts
 

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.

decooney
2,014 posts
 

@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.   

vishu's avatar
vishu OP
28 posts
 

@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

More to discover