KT 150 failure

I bought a set of 150’s early this year for my Primaluna Dialogue Premium.  I’ve always run Gold Lion KT 66’s with no problems. Last week, during silence between songs, I heard this soft fluttering sound thru the woofer.  Cornwall’s.  The slightest tapping of the floor in front of the speaker produced the sound.  I went to the amp which is @6 feet away, and all looked fine- no red tube fail lights.  But the lightest touch to the far left tube really made the woofer flutter.  No red plate, static or popping.  After cool down and restart, tube is quiet until it warms up, then same situation.  Pulled them all and replaced with KT66’s.  All good now.  But I have a geeky question.  What happened with that tube?  In Dynaco Days, I had more dramatic failures.  It’s a fail, but what failed?  Thanks in advance for satisfying my curiosity.  


Right, a microphonic tube. If there's a warranty you should contact the dealer.

Assumed it was finished, but you’ve answered my question.  Thanks. 
Previous failed tubes were never this subdued.   

One of my amps uses KT150s. Terrible reliability; three of the four have failed in the first 250 hours. One for vacuum loss, the other two flashes, loud pops and dead. One of those took out the fuse. Fortunately no speaker damage.

I spoke to the amp manufacturer and he confirmed that others were having the same problem. Very good sounding in a well designed amp but terrible quality, the worst I’ve seen in new production output tubes.


what you say is hardly surprising, given what is happening in that part of the world where these tubes are made

Fortunately it wasn't something catastrophic.   I would definitely pull that tube before something bad happens.  I have had fairly good luck with other GL tube types but I did have a KT 66 red plate and a KT77 lose vacuum.   

I recently have been paying the match and low noise fee on new tube purchases , so far so good .   I have a tester but I feel more comfortable if they are matched on something like an Amplitrex or similar .

I have had great performance from my KT150’s and 170’s all purchased prior to the issues in Russia. Be mindful that all these Russian Tube Factories are US owned. How old are these 150’s? Meaning when did you buy them?

I bought these in March from an outlet in Canada.  About the time that tubes were getting scarce.  I really just wanted some new 66’s or maybe to try some kt88’s.  All I could locate at that time were the 150’s.  Gave me a good excuse to move farther up the chain.  Long break in, but they sounded just great.  I’m hoping that this is a one off.  4 x expensive is a commitment I guess.  If it happens again too soon I’ll cut my losses and retube with 66’s maybe.  No whining from my end.  All this improves the quality of my life, every single day

A microphonic or futzy  tube is part of tube ownership.

I've been pretty fortunate with my PL't tube consumption. NOS  US power tubes held up with 6 years of heavy use and had 2 PL branded Chinese EL34's go after couple years of moderate use.

I don't have any desire to try the KT 150 based on user  tube life reports, and price vs. expected tube life. PL HP user-8x power tubes of something over $50+ makes me think twice about what to try.

Yup. Almost went with HP, but being retired, the cost of 8 tubes steered me to the Dialogue Premium.  Happy Happy.  This amp is on, a good portion of every day.  Tubes are the “cost of doing business”

" Almost went with HP, but being retired, the cost of 8 tubes steered me to the Dialogue Premium"

I'm rounding 3rd base towards retiring. PL seems to fit retirement lifestyle-just turn it on and enjoy. 

Excellent "base" to use better than average sources/speakers. 

Happy listening during your retirement years.

We’ll my rig only has 4 power tubes and have a load of 88s 120s 150s and 170s. Started buying when tensions were building in Russia. Had some insider info with a couple of joint ventures we were doing in Russia and Ukraine. Also when all the Russian scientist and engineers bailed from NASA in Houston. 

Jerry, off topic, but always like to ask folks what differences they heard between those tubes.  Accepting different amps, rooms etc.  I still like to hear people’s opinions.  I always suspect that differences are there but not earthshaking.  In the same equipment.  If these 150’s don’t work out down the line,,,,I have other observations to mull over.  Thanks 

That KT 150 went microphonic. I have been running KT 150s for three years and they still are cranking away and sounding good to my ears. I think a lot of power tube life depends on the circuit design and how hard they are driven

George, thanks for the post. As a tube enthusiast I learn from my fellow Agoners. Over the last couple years I’ve had 2 power tube failures with my Had Inspire. The first was a SED Winged C 6550 that had a catastrophic envelope failure. Big pop and a fair amount of white smoke. I happened to be standing at my stereo and flipped the power off. I didn’t notice any sound from my speaker and no amp damage. The second was a brand new pair of new production Gold Lion KT-77’s, one let go damaging the amp and creating a hellacious pop through my Zu Omen. I sent the tubes to Mr Had with my amp for repair. He said it was a “ Runaway plate voltage issue with the tube failing”. I’ve recently purchased a pair of KT-150’s from Upscale and I’m hoping that their sales pitch and expensive price netted me a pair that’s “ More Reliable “ than the average KT’s that people mention. Time will tell, and thanks to you and the others for sharing info as I learn from you guys. Happy Listening , Mike B.