ST-120 & Power Tubes

I am a new member to this forum; however I have been using tube audio for more than 45 years.

That said; I have one of the first 3 ST-120 kits from Bob Latino. I am using a Dynaco PAT4 preamp (I know it is not valve equipment but Bob's kit makes it sound incredible). My speakers are Heil AMT10B's purchased new in 1974. The driver tubes on the amp are Mullard NOS 12AT7 and the rectifier is a JJ5AR4/GZ34.

The reason that I have joined this forum is to discuss power tubes. Over the last two and a half years I have gone through three sets of KT88's and am now on my fourth set. The first set was JJKT88's which lasted about nine months before catastrophic tube failure. On the second I splurged and purchased Gold Lion reissues which lasted all of two and one half weeks before catastrophic failure. Then I purchased a set of cryogenically treated ElectroHarmonix KT88's that lasted almost eight months before catastrophic failure. These failures make one uptight about the quality control of these manufacturers.

I was bummed about Russian tubes at this point and had read a lot of conflicting information about Chinese products. So to make along story short I took a chance and invested in a set of Penta Labs KT88SC's from Doug's Tubes. They are the sold plate version manufactured by Shuguang which are touted as being Strict Copies of Genalex Gold Lions. I just could not justify $500.00 for the Treasure series or even worse $1300.00 for EAT's.

They have been in the amp for six and a half months now with a little over 300 hours on them, and I must say they are every bit of what I have read about them. Upon installation they biased with no problem and since then I have checked them once a month and have made only one minuscule adjustment. They are steady as a rock, not like the previous sets which required readjustment every three to four weeks.

The sound is quite amazing. On first listen they were every bit as good as the Russian tubes. Now with over 300 hours on them they just seem to get better. The sound stage is open and the experience is like being in the concert hall. The high's are crystal clear, the mids are exceptional, I have been hearing stage noises in the background that I never heard before and can clearly differentiate individual instruments that were just in the "muddle" of sound before. The base response is strong while being clean and not overbearing. The combination of the Penta Labs KT88SC's and Bob's ST-120 kit create an amazing instrument.

Has anyone else experimented with Chinese valves? So far I am very satisfied.

ArlanB

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Hi PeterCapo

I have been running a set of New Sensor / Genelex Gold Lion KT88 tubes in my Mark III amps for about 4 months now. I work from home and my system is playing every day from about 9:15 AM until about 12 at night, even Sundays. At a rough estimate I'd say that those tubes have about 1,500 or more hours on it.

Within about 2 weeks from new, one of the KT88 tubes started making a very faint "rustling" noise, I contacted the supplier (Tube Depot) who said No problem, send the tube back, they'll replace it... I never got around to doing so, the offending tube did not get any worse and the "rustling" is inaudible about 3 feet away from the speaker anyway.

These tubes sound so good that I am willing to put up with it its (reputed) shorter lifespan. I have run them in my ST-70 as well and frankly the ST-70 sounds better (more detailed, deeper and wider soundstage) than with the KT66 tubes from the same manufacturer.

-- 'Jan

I bought a set of Tung Sol KT-120's for my ST-120 to see if they were the equal of my Gold Lion KT-88's. I tried the A-B test with my Gold Lion KT-88's and after a short stint (2 days)with each. I have left the KT-120's in there with 60 mv bias for the last 8 months and they are superb and seem completely reliable loafing along at that bias voltage. After playing them extensively for over 2000 hours they are without issue and were actually cheaper than the Gold Lions. I have never even had to adjust the bias and I check it weekly. Great tubes!

I agree with baddog i have been running the kt120's in my st-120 and i love them. The gold lions that i have used never lasted very long
and i think the Tung Sol KT-120's sound better and cost less.

While your Chinese tubes may be fine, I feel that buying from Doug's may have contributed to your luck. Doug burns in and rematches all his tubes, both power and small signal. Many of the other big name tube retailers simply resell "factory matched" quads of tubes..they may have been matched when they left the factory, but after 30-40 hours in your amp, you can expect at least minor drifting of bias and current draw. Doug's a great seller who takes the time to do things right. The only time I will buy new manufacture tubes elsewhere, is if he doesn't have what I need, which has been rare.

I'm running a Quad of the Shuguang Treasure KT88s in my ST120 that I got from Grant Fidelity. These sound great. I had a quad of the KT88 Gold Lion Re-Issues. If I had to do it all over again I don't know if I would. The reason is that the Gold Lions sounded great as well.

The Shuguangs I did notice had a "decent" sound for starters. I was worried I spent a lot of money on a KT88 downgrade... I've got about 200 hours on these KT88s now and they are great. I think Shuguang overall is doing a good job converting people to the products they sell. NOS is spendy so it is nice to see some options from China. These look like well built tubes and sound great as well. I hope these hold up. This thread had me a little worried.. I thought the power tubes went years and reading your post on the times you had before a failure have me a little worried.

PS - The Shuguang Psvane (Pavane) series is also interesting. I don't mean to take this thread off the power tube topic... But these tubes look nice... More built up like the NOS tubes you see... Shuguang looks like they are trying to build some nice tubes worth a try.

Shuguang Psvane (Pavane) in the 12AT7 I was thinking of trying in the center spot of the VTA in my ST120. But I am done buying tubes for a while!

One of the reasons that I used two matched quads of the Tung-Sol KT120's in the M-125 monoblock prototypes is that they draw more current than any KT88 and would be harder on these two amps. If the amp was going to blow a fuse or show any other sign of distress, it would do it a lot quicker with the KT120's. Neither M-125 ever showed any sign of distress or ever blew a fuse. An interesting sidelight was that the two M-125 amps seem to play louder better with the KT120 tubes than with KT88 tubes? Strange ? I would have sworn that the amp had more power with the KT120 tubes in there? Then ... Yesterday I ran across the thread below on the DIYaudioprojects.com web site in which one KT120 user (mwhouston) did some measurements and claims that he got more power in his amp just by switching out the KT88's for the KT120! Maybe the amps do produce more power with KT120's? - AND - that may be true for any amp using KT120's in place of KT88's ?

Tung-Sol KT120 users and abusers thread

Bob

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This guy sells reasonably priced cryo-treated tubes that are given a 24 hour hour burn-in after the cryo-dip and matched on the Maxi Matcher. I purchased a quad of EL34EH from him because I wanted to try cryo'd tubes. They absolutely sound different from another quad of the same Electro Harmonix tubes that I have. Give 'em a try.
http://stores.ebay.com/SaleRCS

If you are going to buy the Shuguang Treasure line I'd call Grant Fidelity... Talk to the woman who runs the shop. She is from China and has a relationship with the Shuguang manufactures and Grant is the licensed dealer. Talk with her about the extra testing and the tube screening that they do. They filter out about 30% of the tubes and send them back. these are tubes that would probably work for years but don't have passes on the extreme tests ran on them.

This is similar to the testing process of the EAT line of tubes... EAT makes many tubes and then does some intensive tests to get out to customers only the best of the best... Which is why they cost 1,000+ for a quad.

KT120's in a ST120 amp... I know Bob ran tests on these tubes in a 120 for heat etc.. Did the amp put out any extra wattage to the speakers like this forum link observed? Just curious.. I don't have the 120 tubes or equipment to test.

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FWIW,
Just bought a set of tubes from the TubeStore.com. On the tube I wanted (GL KT 88s), they happened to be $40/ea. cheaper than the TubeDepot.

Another bonus, the appeared to ship within Canada -- no "duty" or whatever they call that nasty 20 to 30% charge on US goods coming over the line.

Still, tubes aren't cheap!