Damned JJ KT's......anyone else having problems...?

Flat5th

Active Member
Joined
Apr 12, 2020
Messages
124
Reaction score
93
I bought a matched set of JJ KT66's for a boutique I own. I love JJ's KT66's and have generally had good luck and longevity from them. However, the last set I put in developed a spitting hiss in one of the power tubes with only about 10 hours of playing time on it. It's in one power tube. I just knew it was a preamp tube as it sounded like typical preamp tube spitting. But nooooo...one of my brand new, not to inexpensive power tubes. Anyone else had problems with JJ KT66's that sound like this ? Not happy.....
 

Kelia

Well-Known Member
Joined
Feb 26, 2018
Messages
1,775
Reaction score
2,355
I bought a matched set of JJ KT66's for a boutique I own. I love JJ's KT66's and have generally had good luck and longevity from them. However, the last set I put in developed a spitting hiss in one of the power tubes with only about 10 hours of playing time on it. It's in one power tube. I just knew it was a preamp tube as it sounded like typical preamp tube spitting. But nooooo...one of my brand new, not to inexpensive power tubes. Anyone else had problems with JJ KT66's that sound like this ? Not happy.....
I have a pair and all good so far . Bought a few KT77's because Bob Gjika loves them but
they have to be between 30 and 34 current wise and that's what I have.
Now with the ban on tubes , when you install a new set in your amp , it would
be a great idea to kneel down and pray the Mighty God of tube longevity .
 

Georgiatec

Well-Known Member
VIP Member
Joined
Apr 23, 2010
Messages
5,975
Reaction score
6,132
Location
Looking for something I don't remember what.
I have a pair and all good so far . Bought a few KT77's because Bob Gjika loves them but
they have to be between 30 and 34 current wise and that's what I have.
Now with the ban on tubes , when you install a new set in your amp , it would
be a great idea to kneel down and pray the Mighty God of tube longevity .
Run a cooler bias to extend tube life. 🙂👍
 

Eric'45

Well-Known Member
Joined
Oct 2, 2021
Messages
515
Reaction score
1,377
Location
Germany
I've been using JJ KT77s for Years, never had problems. But I guess a Tube failure can happen always, at any Time. I've had a Rectifier Valve just go *pop* the second Time I was powering up the Amp after it was installed. Some say Tube quality was better in the old days and go NOS for that reason, but I'm not old or rich enough to confirm that.
 

XTRXTR

Well-Known Member
Joined
Feb 14, 2021
Messages
901
Reaction score
1,026
Location
Some City, USA
In 45 years I've had a tube blow once, HT fuse etc blew as it should, no damage to the amp. I have always run cool, I like the tone cool. I have replaced many tube sets before they go boom. I did have a mismatch once, Lord VALVE replaced them without any hassle.

Shuguang kt66 I've had no problem. I usually run 5881 though.
 

lespaul339

Well-Known Member
Joined
Dec 28, 2010
Messages
1,724
Reaction score
3,339
Location
Iowa
I've never had any issues with mine. JJ is all I use too.
 

Spanngitter

Well-Known Member
Joined
Jan 22, 2019
Messages
251
Reaction score
258
Location
Upper Palatinate / Bavaria
I bought a matched set of JJ KT66's for a boutique I own.
What amp, what plate voltage, which Bias?
just stating that there was a valve fail is not enough to point into a possible direction of root cause. KT66 are a special breed and a lot of „Amp Designer“ do not respect their limits…not as worse as in most EL84 Amps but possibly critical for the tubes.
 

jeffb

Well-Known Member
Joined
Oct 11, 2011
Messages
1,831
Reaction score
3,926
FWIW- I always buy from a reputable dealer who matches AND burns them in (and some have guarantees for X days) or pay extra to have them do so. IME, if a power tube is going to fail it will either be after a long period of time getting pounded OR within several hours of initial play time. Burn-in seems to get me long lasting sets every time.

The only times I have ever had a problem with JJ power tubes is when they were new OEM equipment (marshall, Orange, etc) and obviously don't get the burn in. I've not had any issues with New Sensors either that got burn in. I've had bad luck with all the Shug/Sino power tubes , burned in or not
 

Flat5th

Active Member
Joined
Apr 12, 2020
Messages
124
Reaction score
93
What amp, what plate voltage, which Bias?
just stating that there was a valve fail is not enough to point into a possible direction of root cause. KT66 are a special breed and a lot of „Amp Designer“ do not respect their limits…not as worse as in most EL84 Amps but possibly critical for the tubes.
To be honest I have not fired the amp up in a few months ( which begs the question why am I so worried about the tubes ) and when I did I was playing a Nord Electro 4D keyboard through it. Tube amps help those digital tone wheels in organs sound a bit more organic. They are probably on the cool side. I have always had really good luck with JJ tubes and thought the KT66's sounded very robust and full. I have not dug in deep enough checking other values. The amp is an Oldfield JC-50. Basically a late 60's Marshal 50 watt bass clone with some bells and whistles added. One thing that is cool is the slope resistor is on a value switch. 33mu or 56mu. Not really a ton of difference. The 33mu is a tiny bit more full. There are a couple of other cool tricks. Paul is great and will do whatever you want. He is a low voltage mid gain kind of guy so his amps will not be for everyone. However, the build could not be better nor the quality of components. I have heard his Fender 5E3 version is a real fire breather if you want him to set it up that way. It's om my amp list. I am getting my amps back in shape and remember well being very irritated at having to order a new set of tubes. You guys are right. I best do it quick or who knows what is up. Thanks everyone for the information and your experiences. It sounds like we have all had good luck with JJ tubes. Anyone else please chime in and tell how your luck has been with JJ KT66's. Again, to my ears they are really good, robust sounding tubes with very musical gain qualities, Just died too quick this batch. They are not endangering the amp, but it's enough to be annoying. Thanks again for all the replies
 

2L man

Active Member
Joined
Sep 30, 2020
Messages
209
Reaction score
139
I don't remember details but you should find instructions on HiFi forums how HiFi guys treat tubes in an oven to cure some issues?
 

Spanngitter

Well-Known Member
Joined
Jan 22, 2019
Messages
251
Reaction score
258
Location
Upper Palatinate / Bavaria
Anyone else please chime in and tell how your luck has been with JJ KT66's. Again, to my ears they are really good, robust sounding tubes with very musical gain qualities, Just died too quick this batch. They are not endangering the amp, but it's enough to be annoying.
Here I have a 50W and a 100W Vintage Modern, an Astoria Classic and 2x JTM45/JMP50 (Lead and Bass) Homebrews equipped with KT66. All of them had been JJs with no issues reported at all, however just for curiosity I replaced the Set in one of the Homebrews with CP TungSols without noticing larger changes in Tone. I usually keep them in a range of 60-65% max Dissipation, just ensure that you have proper Grid Resistors installed as CP KT66 does absolutely not tolerate their absence or incorrect Values. So having one of your tubes pop out prematurely would indicate to me that there might be an issue like this....
 

Latest posts



Top