Life of KT 150 Tubes

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.