KT120's with cj amps

[turntable]

I bought KT120's over 3 years ago, put them into the teflon prem8a's for a few weeks. Then took them out and put them in their boxes for 3 years as they were too bass heavy and went back to my Tung Sol 6550's.

I just swapped the listening room with the smaller TV room as I have always had bass gain issues that muddied the sound somewhat.
Go figure the smaller room sounds quite a bit better in the bass - less of it as in boom. I decided a few days back to pull the KT120's out of hibernation and see how they sound.

WOW, a whole lot better. They still have lots of bass, but I can hear deeper in the bass with better texture. As Coppy said, transients seem a lot better. That seems to coincide with the more forward vocals, guitars, piano and other lead instruments. 3d image is better as well.

Overall very happy that I pulled them out and put them into the prem 8a's. Will happily play them for the next few weeks, then go back to the 6550's to revisit.


What other cj amp owners use KT120's?

Tell us your story.

Cheers

[Bill Stevenson]

I have an ARTsa which was designed with KT120s of course. I know the KT120 is the tube of choice in new designs from other manufacturers as well. Recently there was a very brief mention of them in the British magazine HiFi World in which the KT120 was commented upon in comparison to the KT88. That comment favored the KT88. That is the first less than fully favorable comment I have ever read or heard on the KT120. Amps equipped and able to handle KT120s always sound better to me than any other.

[ronenash]

I also use the KT120 in my LP125mSE and love them. I believe current production power tubes are just as good if not better than NOS. The KT120, GL KT88 and Mullard KT88 are all fantastic tube which IMO do not fall behind the mythical NOS types. The new Mullard KT88 if an absolute bargain. Virtually indistinguishable from the GL KT88 and can be had at much lower prices. I plan to stock on them before the price goes up.

[Briz Vegaas]

KT120 in LP70s here. No brainer over the standard OEM tubes for this amp. Been backwards and forwards a few times but the original tubes never stay in long. KT120 is better across the audio spectrum.

[Bill Stevenson]

Out of curiosity have any of you replaced a set of KT120s yet? If so, how many hours should a set last and from whom did you buy the replacements?

[tonytsui]

I have been using KT120s on my ART mono amps since January 2014, and have used the Amplitrex AT1000 tester to monitor tube life. Whereas emission, transconductance, gas leakage all remained stable, the major issue is with Heater to Cathode leakage. While Tung Sol's spec is less than 30uA, a new KT120 can go from 0 when new to over 30uA in a month. This problem is serious as failure rate is extremely high - I have 16 being used right now, but around 40 have failed so far since Jan 2014.

I do not profess to have a deep knowledge of tubes. After asking around, I was told a high H to K leakage upto 100uA is acceptable and it would cause hum. Emailed Tung Sol : reply was that they have no such problem and suggested problem is on my side. I proposed to ship them my failed tubes at my expense for testing, they didn't answer. Emailed CJ and explained this issue, response was that they would refer my problem to Tung Sol.

At first I accepted 100uA as a limit, but after changing my speakers to Magico Q7, the upper mid-range glare became very annoying, especially for massed strings. Then I took out all KT120s that measured over 30uAs and replaced it with good ones. The glare is much reduced.

My experience probably contradicts a lot of good reviews and user experience. Also for info : I bought my KT120s from various sources and at different times, so it is not a batch problem. If my AT1000 is at fault, then it also measures good ones.

[Briz Vegaas]

Magico Q7. Very very noice. Very very revealing. Heard them in Singapore on Vitus gear, awesome. My benchmark in fact.

I don't doubt your observation on glare, but one thing i an notoriously bad at is identifying the source of a particular characteristic. Thought my Naim DAC was a little too midrange focused after comparing it to a Hugo. Then i upgraded to the latest Audirvana software. Suddenly the balance is just fine. Not too much of one thing or another.

My KT120s are about 10 months old now. The previous set were clearly past it but they were in the amp when i got it and despite being a demo that amp had been around for years and years before i bought it. Listing to a simple pop album right now. Beautiful Freak by the eels. Sounding great to me. At the price i would be happy with a couple of years out of them before comparing them to a new set to see how they are travelling.

[Bill Stevenson]

There is a nice write up in the November issue of The Absolute Sound on the Magic Q7 MkII if you haven't seen it. I am not aware of any particular issue with KT120s. Could there be a problem with your amps? I am thinking maybe a voltage swing caused by your local power company or frequent lightning strikes or something. Your experience doesn't make sense based on the overall reputation of Tung Sol KT120, which is quite good as far as I know. I would call cj again and ask for Jeff. Something ain't right.

[microstrip]

Originally Posted by tonytsui

I have been using KT120s on my ART mono amps since January 2014, and have used the Amplitrex AT1000 tester to monitor tube life. Whereas emission, transconductance, gas leakage all remained stable, the major issue is with Heater to Cathode leakage. While Tung Sol's spec is less than 30uA, a new KT120 can go from 0 when new to over 30uA in a month. This problem is serious as failure rate is extremely high - I have 16 being used right now, but around 40 have failed so far since Jan 2014.

I do not profess to have a deep knowledge of tubes. After asking around, I was told a high H to K leakage upto 100uA is acceptable and it would cause hum. Emailed Tung Sol : reply was that they have no such problem and suggested problem is on my side. I proposed to ship them my failed tubes at my expense for testing, they didn't answer. Emailed CJ and explained this issue, response was that they would refer my problem to Tung Sol.

At first I accepted 100uA as a limit, but after changing my speakers to Magico Q7, the upper mid-range glare became very annoying, especially for massed strings. Then I took out all KT120s that measured over 30uAs and replaced it with good ones. The glare is much reduced.

My experience probably contradicts a lot of good reviews and user experience. Also for info : I bought my KT120s from various sources and at different times, so it is not a batch problem. If my AT1000 is at fault, then it also measures good ones.

conrad-johnson connect the filaments of the tubes to a resistive voltage divider fed by the HV to control leakage current of cathode to filament. Perhaps you should contact the factory about this problem - maybe changing one of these resistors can solve the problem.

[tonytsui]

Originally Posted by Bill Stevenson

There is a nice write up in the November issue of The Absolute Sound on the Magic Q7 MkII if you haven't seen it. I am not aware of any particular issue with KT120s. Could there be a problem with your amps? I am thinking maybe a voltage swing caused by your local power company or frequent lightning strikes or something. Your experience doesn't make sense based on the overall reputation of Tung Sol KT120, which is quite good as far as I know. I would call cj again and ask for Jeff. Something ain't right.

Yes I have read the review at the TAS. Have listened to the Mk II a few times, still considering whether to upgrade. The MK I in my view is better at playing pop/jazz rather than classical. The glare on violins, especially close miked ones, is really annoying.

Some further info : a friend who also uses the ART mono amp bought around 20 Tung Sol 6550s and I measured these when new with great results including very low H to K leakage. A few months later all these tubes failed in the H to K leakage tests.

I also had 16 KT120s from CJ which also failed like the others.

Yes I am confused as to the cause of all these.