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In Reply to: RE: Shuguang Treasure KT-120 or Tung Sol KT-120? posted by JerryS on April 06, 2016 at 10:29:28
Hi Jerry.
Well I have some good news and bad news.
The good news is that the Treasure KT120s, when functioning properly, are one of (if not the best!) sounding tubes I have used in my Rogue Stereo 90. They are WAY better sounding than the Tung Sol KT120, which I find to be a very average sounding tube in the Rogue.
Now the bad news. Here is my story. I ordered a quad of Treasure KT120s from Rachel at Grant Fidelity. After almost a month the tubes arrived and were installed in the amp. One tube would not bias (bias shot up to over 100ma on the meter and would not come down). The quad was sent back and after a few weeks a new set arrived. Rachel advised that the bad tube had been gassy. The new quad tested stronger than the first quad and biased fine and the bias held steady. For two months no problems, great sound.
Earlier this week, I was checking the bias on the tubes. I bias them for 35ma on the meter as recommended by Rogue for KT88. One tube of each push pull pair was measuring high at around 50ma and the other tube in the pair was low at 25ma. Up to this point bias had held pretty steady. I adjusted the high bias tube down and the low bias tube up until all tubes were at 35ma again. Played another album side and checked again. Now the tubes that were low bias and I had turned up were at 50ma and the tubes I had turned the bias down on were at 25ma. I tried adjusting bias for the next couple of hours but could not get them to stay at 35ma. It almost seemed like the push-pull pair were fighting each other for current. The sound was still good, but I was concerned about the tubes and the amp so I removed the KT120s and replaced with Psvane grey glass KT88 (those also smoke the Tung Sols in the Rogue IMO).
I have not had a chance to test the KT120s but I suspect gas. Over the weekend I will do so and if they test OK will try to bias them in the amp again.
I really liked the sound of the Treasures. They have terrific bass like the Tung Sols, but the midrange is rich and holographic, whereas I find the Tung Sol dry and clinical though the mids. Hope I can resolve my biasing issues, the Treasures rock!
Edits: 04/07/16Follow Ups:
Interesting report. Thanks for sharing. I haven't tried Shuguang Treasures but my Tung Sol KT-120s have been chugging away for over 3 years and the bias voltage has been totally stable the entire time. They may not sound as good as the Shuggies but they have been very reliable at least in my Emotive Audio Vita amps.
My favorite sounding tubes in the Emotives are Genalex KT-77s (reissue). I just wish they had a bit more power. The Genalex KT-88 is a distant third place.
You might like the sound of unbalanced or tortured tubes :-)
Well as I mentioned in my post Chip, they held bias steady for the first two months use, and during that time they were as good or better than any output tube I have used in the Rogue and I have tried a ton of different tubes. I have only had trouble biasing them this week.
Thanks for commenting!
Edits: 04/07/16
"Earlier this week, I was checking the bias on the tubes." Unless you check it every few days you do not know when the fault occurred. If you do check them constantly...
Actually Chip, I run the amp without the top off so I check the bias just about whenever I use the amp. It is very easy to do with Rogue amps and only takes a minute.
Do you have anything constructive to add to this thread or do you just sit there and nitpick other people's posts?
Edits: 04/07/16
When one claims massive differences in sound quality between two otherwise comparable tubes there is usually more going on. These are not standard KT88 tubes and each has its own electrical properties which may or may not be compatible with the voltages, amperage and loads presented in your amp. Usually when there is consistent failure of a tube, the problem is with how and amp is working with a tube rather than the tube itself. This is the problem that drives tube dealers mad as they keep sending customers good tubes only to have them destroyed by the customer and having to replace them. I am not saying there wasn't a problem with your chinese tubes before you installed them, but that is what my point was: don't assume that you can pass judgement on differences in tubes unless you are 100% certain of the operating conditions (IE using the tube the amp was designed for rather than something that is "compatible"). For such massive differences to be so readily discernible to you points to something other than you listening to the tubes being run optimally.
Here are the facts:
1) The OP JerryS asked for (subjective) opinions of the Tung Sol KT120 vs the Treasure KT120 for use in a Rogue Audio Stereo 100. I own and have used both tube types in a Rogue Audio Stereo 90 which is a very similar amp.
2) Before buying the Tung Sol KT120, I contacted Rogue Audio and was assured that KT120 were fine to use in the Stereo 90.
3) I clearly stated in my post that the Treasure KT120s were one of the best sounding tubes IN THE ROGUE AUDIO STEREO 90 and outperformed the Tung Sols IN MY OPINION IN THAT AMP.
4)I never said that any tube had failed, only that after 2 months the bias on the Treasures had become unstable in THAT AMP and I would check the tubes for gas or other problems. As stated above, I was assured the amp is fine to use with KT120 by Rogue, and have not had any biasing problems with the Tung Sol KT120.
5) I never used the term "massive" in my comparison, I said the Treasures were WAY better in my opinion in the Rogue Stereo 90. I much prefer the sound of the amp with the Treasures, which was what Jerry was asking (as he intends to use the tubes in a very similar amp). The difference was major to me but might be somewhat less to another listener.
6)Since both sets of tubes are KT120s being run in the same amp, my opinion of the sound is not affected by the tubes being run optimally or not, since both tubes are the same type and subjected to the same operating conditions in the amp (which again are fine for KT120 according to Rogue). Your last sentence makes no sense at all.
7) I was only trying to help out JerryS, since I have a very similar amp and have used both types of tubes he was asking about, and he was grateful for the help.
I don't know why my subjective opinions have to be scrutinized by you Chip647. Its my opinion, and if you have a different opinion that is fine. Your entitled to state that opinion (do you actually have an opinion on the tubes in question?). But you are not entitled to belittle my opinions based on incorrect facts.
Edits: 04/08/16
Whatever the so called facts, what IS a FACT is that the grid resistor should be less the 51k or else thermal runaway might occur.
And that seems to be what happened. The amp might not be suitable to use kt120, and that is the main cause of the problem.
I would think Rogue Audio would be aware of the value of the grid resistor and would take this into account when recommending tubes for use in their amps.
There was no thermal runaway, no red plating, etc. The bias was not holding at 35ma and was varying by plus or minus 15ma or less. This was after holding steady bias for 2 months.
Further, none of the above problems occurred with the Tung Sol KT120 (same tube type as the Treasures) which held vary stable bias in the amp. They just did not sound as good.
Unstable bias could indicate that the grid resistor is not small enough to keep the tube in a stable condition.
And a vendor that "don't have a clue" is not uncommon.
Why not open up and examine the value of the grid resistor ( or check the schematics) so we could end this (sub)discussion.
Hmm... if one cannot believe the manufacturer as to what tubes are compatible, then everyone is just screwed, ehH
You know, this is the second time in as many weeks that you've denigrated the use of "alternate" tubes in an amp. It seems to me that you have been wrong both times.
Is the problem what Chip647 complained about? Your moniker indicates you are a dealer; are you sensitive to the idea of "compatible" tubes because you've been burned?
Cerebrate!
I did not know the Stereo 90 could use the KT-120's. Rogue's site seems to imply KT-90s at most.
Indeed, could this be an amp compatibility issue? The Tungsols always settle in rather quickly in my M-180s. In any case, $700 for a re-tube is not compatible with my wallet.
kt120 , at least in "modern tung-sol" variant needs a grid resistor of less then 51k. If you have a larger one, as one typically have on a kt88 amp, thermal run-away might occur.
http://www.mif.pg.gda.pl/homepages/frank/sheets/084/k/KT120.pdf
A big THANK YOU for your post. There is only one thing that bothers me more than questionable sound quality and that is poor reliability/equipment problems. In other words, I would gladly "suffer" with the sound of the Tung Sols (although they ain't so bad) than create problems in my new amp with tubes that have poor quality.
Please update your findings when you can.
Thanks,
JerryS
It may be as simple as the tubes needing more hours and the Treasures need a lot. The internet is full of posts dissing something the poster has not used. Don't make a hasty judgement. ;-)
Thanks for the comments Les.
I definitely intend to put the Treasures back in and let them run some more.
Hopefully they will stabilize again.
Mendel,I think the Treasures are excellent tubes and the long burn in is real. I have seen posts where folks gave up on them prematurely. I don't think your tubes are defective they just need hours and watching the bias during the process. I'm not Jim McShane but I do know that the bias drifts during the settling in period.
FWIW,I get mine from Hanshare Electronics on the auction site. To date, an honest and reliable seller.
Les
Edits: 04/09/16
I got home today and ran the Treasure KT 120 through a complete testing on my Stark model 12-22A mutual conductance tube tester. There are no shorts, the mutual conductance tests very strong, the gas test was negative on all tubes, they even do very well on the extreme condition (life) test.
I can't understand why the bias became unstable recently. Could they still be breaking in? I understand that the Treasures require a lengthy break in.
I intend to reinstall the tubes in the next day or two and see if they stabilize. I hope so, since they are great sounding tubes.
Has the bias been holding steady for the past 2 weeks?
Just following up.
Many thanks,
JerryS
The bias on the Treasure KT120 won't stabilize and even seems to be getting worse. I'm tired of checking the bias after every record side and finding a tube or two off by 20ma or more. Just not enjoyable. They did sound good but I can't take it anymore.
Just to confirm it is not some amp problem with KT120s as tubular suggests, I replaced the Treasures with Tung Sol KT120. The bias has been rock steady since yesterday afternoon with these.
The main difference between the Treasures and the Tung Sols is "bloom" in the midrange and "air" around instruments and voices. There just is not nearly as much with the Tung Sols which leads to a dryer, more mechanical, less real sound. In my opinion, in my amp.
Too bad, the Treasures are great sounding tubes. If the fix the quality problems and get dealer testing here in North America, they will be a great choice for many amps
Thanks again for following up. I'll keep using the Tung Sol KT120s and fine tune the sound with different small signal tubes. I already installed 60s NOS Mullard 12AX7 (from Vintage Tube Services) which added a bit of warmth and removed some edge in the treble. I'll probably go back to VTS for Mullard 12AU7s.
The Rogue Stereo 100 is a fine sounding amp with stock tubes so these substitutions are only making it better.
Happy listening!
JerryS
Well I have kept the Tung Sol KT120s in my amp for the last week or so. Perhaps I was a bit harsh, not a terrible output tube if you get the tubes in front right. Definitely try a good 5751 in the input spot they seem to have better synergy with the Tung Sols than any 12ax7s I have tried. Using Sylvania black plate 5751s with Sylvania 6SN7W drivers.
Enjoy the roll!
And the value of the grid resistors are ??
Hi Jerry:
I have not had much chance to use the amp in the past few weeks. Bias still jumping around a little last time I was listening, but sound was good. This weekend I will have more time and will update my findings.
What is the value of the grid resistors ( G1 to ground ) ? As told before,
to high values might cause unstability in the KT120 tubes.
According to tung-sol datasheet 51k is the highest allowable value when used in fixed bias.
Mendel,
I'm using Shuguang Treasure KT66z's in an auto-bias single ended amp and they sound better *to me* than of old production 6L6's I have. They do take a long time to settle in and it is possible that the bias will drift until they do. BTW, the Psvave UK 6SN7 really complements the Treasure tubes.
Les
All tube pins and sockets are clean and tight. It could be as simple as that.
Cheers!
Jonesy
"I know just enough to get into trouble. But not enough to get out of it."
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