gofar99 Messages: 1902 Registered: May 2010 Location: Southern Arizona
Illuminati (5th Degree)
Hi everyone, especially tube lovers. I have confirmed from other users that most of the Tungsol KT120s are microphonic. Some badly so. Those you need to send back. On many others just tapping the glass will make them ping the speakers. It is not always a problem, but in a location where there is vibration it can be troublesome. I use them in a number of amps and they really have an excellent sound quality...just a sensitivity that I could do without.
johnnycamp5 Messages: 354 Registered: June 2015 Location: NJ
Grand Master
Exactly.
I had to send my first quad back because of high micro-phonic noise (two without even touching/tapping them)...
The replacement quad of 120's are also rather micro-phonic (but only when tapping them).
My quad of JJ KT88's are barely so even while tapping them...
gofar99 Messages: 1902 Registered: May 2010 Location: Southern Arizona
Illuminati (5th Degree)
Hi, I still find even the best KT120s slightly sensitive to microphonics. Not objectionably so, but they can. I don't have any real issues with the JJ KT88s though. You have to tap them hard to get any noise.
Even though they can be made to ping, I like the sound of KT120s in push-pull ultralinear configuration at 8K loading with 450B+ and 65ma each. The sound is really special and tube life is likely in decades.
Wayne Parham Messages: 18676 Registered: January 2001
Illuminati (33rd Degree)
Why do you think the KT120 tubes are so sensitive? Do they have thinner elements that are easier to vibrate?
I would have thought any tube with construction that allowed anode/cathode vibrations to be microphonic to some degree. As the cathode and anode vibrated closer and further, it would change characteristics. Same for any of the control grids, I would think.
gofar99 Messages: 1902 Registered: May 2010 Location: Southern Arizona
Illuminati (5th Degree)
Hi, Kind of unknown, but a guess would be that some components are intentionally made loose so that they can expand when the tube gets really hot. Mine are barely sensitive when run at high dissipation in the big amps in class A (145ma at 450V each). They are more sensitive when run in the lower power amps (that have great sound) at 63ma and 450V. Really neither is objectionable as all my gear is on solid stands and bases. I can see how ones on flimsy ones might pick up sounds from the speakers or footsteps and such.
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