KT120 SE Tube Amplifier: Junk Tubes, now what?
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- Опубліковано 16 жов 2024
- Well some problems have arisen in use and it has nothing to do with the iron or the amp design, it's about the lack of QC on these Russian made power tubes. It seems like this has been an ongoing issue, and now given the war etc, it's just gotten worse. Here is an old thread on DIY audio highlighting the issues I have run into:
www.diyaudio.c...
I wish I had discovered these issues before I embarked on this project, this is super depressing. It's not like these amps are unusable, I now just don't believe it's possible to meet the design specs I designed these around.
This series is a DIY project building a pair of single ended, ultralinear KT120 mono block style vacuum tube audio amplifiers. The goal is a pair of high power single ended amps, using only high quality parts, with as few things in the signal path as possible.
This project is using output transformers from Thermionic Labs, custom made to use with KT120 output tubes, which you can buy here:
www.thermionic...
They also should have power transformers and chokes for this project available.
You can send me links and messaged at:
www.skunkiedes...
Here is my Patreon, as well as the donation page at my site, if you feel so inclined to help fund some of the future projects for the channel!
www.patreon.co...
www.skunkiedes...
Here is where you can buy T-shirts and other Merch with my fun logo.
skunkie-design...
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Awwww ~ That's heartbreaking! They look so good and I can feel your disappointment. I know if I was in your shoes I'd be so frustrated too. I'm still playing catch up on the series, but thanks for taking us through all of this. I've learned so much from your channel and I really appreciate all you do.
Keep watching, I didn't give up :)
Just went on ebay..British made are between 300-400 each. Which is about twice what they cost 5 years ago. The better news is that you don't need to get a matching pair. Someday I may try and build these. Really appreciate your effort and sharing it.
Yes prices are rising fast ..........look at the 6550 TUNGSOL ......I cherish those tubes .
Indeed no need for a perfect matched pair !
Everything is inflated due to our lustrous governments bending us over the barrel, om in los angeles at the beach and paying out the bumb for stupid things . I started last year stocking up on what I know I need and want for the next 5 years just because I know we are doomed and it will be where we won't be able to find them maybe due to businesses failing. Who knows , that's why I went for broke to keep a inventory. Thanks God I wind my own inductors , the cost of inductors is what's getting really out of reach .
This is a great video - thank you for sharing your findings! The KT120/150 tube issues you found is super helpful. As others have mentioned, KT88 may be the answer with a couple of design tweaks. I look forward to your next video on these monoblocks!
Hopefully this war ends soon and decent tubes can be had again. I've been holding off on building these monoblocks simply because tubes are extremely limited here at the moment.
It sucks that the tubes are letting you down but this is also a positive. You have a pair of great sounding amps that are just waiting for a pair of quality tubes to compliment the rest of the amp.
I agree with NickP333, you have still given away a huge amount of effort and valuable knowledge to all viewers... Thanks! Also, worst case, you have designed a unique pair of mono blocks with a solid 10 watts per channel, maybe more... Thats a great accomplishment right there! I would still back you and trust your design skills over the "roulette wheel "of Chinese suppliers!
I LOVE your Channel. Such good knowledge and honesty.
I appreciate that!
Nothing really lost. You can still run KT88 's until the quality 120s become available.
Thanks awfully for your honesty. You probably wouldn't hear that from a commercial manufacturer.
I know, right?
It's a high-end Momo Block that will sound the best with high-end KT120 tubes. PSVANE KT120 tubes may be the answer. I have a pair of Prima Luna KT120 on the shelf and will build this amp anyway. There is a big shift towards open baffles and other high-efficiency speakers, so even a reduced output may not be an issue for some. I use Klipshorn speakers with 105db sensitivity, so six watts can rock the room. How about a mA meter and pot to adjust BIAS? People could then compensate depending on the KT120 they have. Could be an easy workaround. Don't give up Stephe
Bummer Stephe. I suppose going the British route as the post below this suggests makes sense. Expensive, but you really have a good amp. That is worth it! 😊
Don't feel bad for us! You have a great project, really well presented and all we need is better tubes - that is OK by me. No need to be down
What "British" tubes are we talking about?
see two posts down@@SkunkieDesignsElectronics
On an unrelated note: it's been delightful to see your subscription count steadily rise over the last few months! 10k before mid October, here we go!
Nice looking project. Why did you not base your design on time tested, very reliable 813 transmitting tubes? I have all the parts now collected to build a pair of such SE monoblocks including new Hammond 1629SEA SE output xfmers. This iron gives me a screen tap if I choose to try ultra linear. Bonus is you can get 40'ish watts RMS from a single tube. Drawbacks are you need a DC filament supply for the direct heated cathode and higher B+ near 1 KV DC.
The 1k B+ is part of the reason.
Using a "fast fuse" and varistor to ground you can protect the bias resistor if the tube blows (eg actual fuse). Of course either way you need a little solder to recover.
Sorry to hear about this. I have 89db speakers and was thinking of building these. Perhaps there is a way to source out some good tubes with some effort.
Hi Stephe.. You could try the Shuguang Treasure KT120’s.. But not sure about them.. Anyway, at least for those with 91+dB plus easy load speakers 10W is aplenty with a very stifff supply and more than competent driver stage..
So, what is the word on these tubes? I just received my quote for the Italian hardware, debating on pulling the trigger... Thanks for the work you put into this Stephe.
I stockpiled enough replacement to last me life time hopefully. But, these days I'm really hesitant to make anything new. I'm a guitar player, I only make instrument amplifiers and mic pre amps. Shuguang factory went up in flames a few years back, they made good affordable bottles, and then the covid and the war after that. Not the best of times for being into valve gear these days.
Bummer - thanks for your honesty Stephe. I have bought most of the components and built the chassis, so this is obviously not what I wanted to hear, but it is what it is ;-) I have quite efficient speakers, so I can live with 10w amps. Don't beat yourself up for trusting the published specs - I haven't heard many negative things about Tung Sol's other tube offerings, so why would you assume the KT120's would be different? I haven't started assembly yet, so the KT120's are still an unknown quantity - I bought them a couple of months ago, so it will be interesting to see how they perform compared with yours
I plan to finish this in whatever form it takes, I just need a break from it for a couple of weeks.
I'm really sad for you, Stephe, and for everyone that was hoping to build these monoblocks with KT120 tubes. I have four KT120 tubes in my Luxman A3600 and it turns out it only works fine because it is a UL PP design, so I can bias the tubes below 70% and still get great sound and over 70W output.
It's a new day, and I'm not giving up on a search for a pair of "bogey" tubes. These amps sound way too good to give up this easy lol.
Hi Skunkie, how difficult would it be to adapt the amps for 805 / 211 tubes?
The KT-150's probably come from the same factory than the 120's?
@@unepanthere Hey yeah! 211's that'd be cool! They're those real big, old school triodes aren't they?
An old boss of mine used to build SE amps with 211's, & actually hand-wind his own 1kV powered output transformers. Some of the sweetest tones I've ever heard.
completely understand your frustration with the KT120's. I run push pull with a quad of KT120's. Since the Ukraine war they have been mostly unobtainable. I bought 4 from China. Plugged them in and immediately red plated and blew a rectifier. Amp repaired, I have been running KT88's in it but I miss the headroom and bass punch. So a set became available from a known dealer and I bought them. They've been playing okay but honestly don't sound up to snuff. I have no way of measuring them. All that said: I have spent a small fortune on tubes for an amp which is optimized for the KT120. What's the point if they are unavailable or of questionable quality? It is a great sounding amplifier......sad
I think I may be finding a compromise setup where one pair of the 4 tubes I have will work. The bass punch these have over a KT88 is so good. It really kills my 300B amp playing rock music for sure.
Ahh, I’m sorry, Stephe. This sucks. Have you tried buying tubes from Upscale Audio? They seem to do extensive testing and have a decent warranty on them. Don’t know the details, but just a thought. Maybe they’d even send you a MP of them to try out if you told them about the channel. You do have close to 10K subs, and will very soon.
You definitely don’t owe any kind of apology. I’m definitely gonna be thinking about ways to possibly fix this situation but who knows….
Thank you for letting us know.
Hi Nick ................getting rid of this family tube disaster .........there are alternatives but they are very pricy .....I would use something like an nos TFK EL156 in this kind of amplifier.
Wow! Very informative. I really enjoyed this series, great looking amps, hopefully things will change for the better in the tube industry
@@frankgeeraerts6243 Hey Frank, always nice to hear from you. I had to look up the data sheet on the EL156, but it looks like a great possibility. It’s kinda like two EL34’s in one tube and also similar to a KT88? Besides the different pin out, that does sound like a great idea. Unfortunately, they’re somewhat high in price for NOS ones. I see that they are still making the tube, but finding a reliable current production one could be difficult. Thanks, Frank. Great idea and alternative to the KT120.
Hi NIck , ..........the current production version of the EL156 ( sino ) is nothing alike the original TFK...........it has an octal pin out and it does'nt hold thespecification ....don't spend money , same problem as the KT120/150/170 .........
Nos is expensive and often obsolete now....butsometimes you can be lucky !
KT90 EI ( not the current russian/sino versions ) .....sometimes you can find those .........connected in triode they work fine...........one of the best bass slams with tubes .....losing a bit in refinement in the medium , but better in tiode !
have a nice day Nick@@NickP333
@@frankgeeraerts6243Hey Frank. Thanks a ton for the response! 👍🎶😊 The only pinout I personally saw for EL156’s have two sets of 5 pins on each side, so obviously 10 pins in total. I checked the price of NOS TFK EL156, and they seem to be going for about $300 - $400 each, which isn’t that bad considering the build. An extra $600 - $800 is just what ya gotta “pay to play” kinda things. If and when I build this amp, id likely add the cost of NOS TFK EL156’s. I inherited my grandfather’s tube collection of at least 500 different ones, which I need to go through again. There’s likely many tubes that’d be useful to me that I didn’t necessarily know about the last time I went through them.
Those rip-off-russian-rats! Sad to hear this! I'm sure you'll come up with something. Your explanation of what causes the red-plating makes perfect sense. As has been mentioned - maybe a '211'?
The reason I look forward to your vids is the way you carry us with you on the journey. We're still here Stephe - through thick and thin!
Too early to mention the next project? My vote is the 4E27 SE that you mentioned a while back. That one captures the imagination! And offers a path to redemption in the quest for a SE amp with decent power. Made in the good o'l US of A. (Non of this dodgy Ruski stuff) and not too expensive to boot.
That or the 6C33. But then again, that is a Russian only tube lol
@@SkunkieDesignsElectronics I'm coming around to the 6C33. By all accounts a rugged, excellent sounding tube if tricky implementation is properly worked out (nice challenge for you). Interesting looking tube and you gotta love the MIG-25 connection. Still not expensive.
In light of lessons learnt with the KT120, I guess some research might be in order to check if the currently available examples are still NOS or new production that may be suffering the same QC fate as the KT120.
For me, exitement levels for this one are a step above the KT120 mono's.
Going to buy a couple in anticipation ... Then you'd have no choice! :)
Update. Seems that you can only get NOS 6C33's. Once gone, they're gone. Plenty around though so all good. 6A heaters!!
Oh man if I had some junk Russian cameras.
I will say though my bronica ETR has been a solid workhorse for a long time. I've always wondered if you would touch on camera stuff as I find there's a lot more photographers out there than I ever realize. Just like building apps there's nothing more satisfying than developing your own pictures.
I feel your pain with the junk tubes and I hope it's all up from here! They are some of the most beautiful boutique mono blocks I've ever seen
I looked at Upscale Audio for purchase of KT120. They are also Tung Sol, are not that expensive at $120 & claim to have quality control in their own internal testing. Unfortunately, they are only selling them to people who have bought Primaluna amplifiers from them. I was wondering if you were into traditional photography seeing that box of Ilford photograph paper on the shelf behind you. Would be interested in your past history with 120 film. It is a bummer after you made such great Mono-blocks to have junk tubes cause problems! I still enjoyed all the videos about the build even though I will probably not build one now. More likely to try one of your designs for the older, out of the ordinary NOS tubes that even for their age will be of a higher more reliable quality.
Yeah, shame these new production tubes are IMHO basically junk for single ended use.
A friend of mine manufactures an integrated tube amplifier. It is designed for KT-120 tubes, but it will also work with KT-150 and KT-170 tubes. His experience is that the KT-170 tube sound much better than either the KT-120 or KT-150. Just another data point for you.
The deal seems to be these work great with a push pull type amp because they are biased much lower.
@@SkunkieDesignsElectronics Yes, there are not many push pull amps that push these larger tubes. There are some really interesting stories from some American tube suppliers talking about the amount they have to test tubes from China and Russia, and the huge percentage of rejects they get. These are from factory "premium" tubes, not just the run of the mill ones. I understand why you feel depressed after putting so much effort into this project.
Upscale only sells KT120/150s to Primaluna amp. owners.
The whole situation just sucks! Going to have to stick to tubes that you can get NOS or tested used.
Dan
Yup, thankfully the company I got the KT150 tubes from is allowing a refund.
Thumbs down to Upscale, but if good KT120's are that scarce, I understand their policy.
There are vendors like Upscale Audio for example that not only test all their tubes before going into stack but also sell matched pairs and quads. They have tong-sol KT120 for $100 and KT150 for $140.
Upscale only sells KT120's and 150's to owners of their amps.
I think there are Chinese versions of the KT120 out there. Just a thought since the amps are built. Since you're willing to spend eight hundred bucks for the output tubes, that puts you within spitting distance of Emission Labs 300B XLS tubes that can put out what you're getting (or rather SHOULD be getting) out of the KT120's. I've used Emission Labs tubes for years and they are amazing tubes.
They SHOULD be for that kinda money, like Wahhh ! Better than paying $300 for factory floor rejects, but they only make indirectly heated - a 300B means quite the rewire...? Isnt there ANYTHING in regular pluggable Octal that does SOMETHING like what it says on the tin/datasheet???
@@petegaslondon Yup, NOS 6V6 tubes. Cheap as chips, made in the millions. Not power monsters but hey, build more efficient speakers then. Or use 5V6 tubes (using the 5V rectifier winding) and you get NOS octal power tubes that cost five bucks. Or use Loctal versions of the 6V6, even cheaper.
Yes, Emission Labs tubes are expensive but they come with a five year warranty that they make good on. I have a couple of pairs that are ten and eight years old and are still going (and test) strong (45 triodes) and when you do the math on the dollars per hour they are truly worth it. Better and longer lasting than NOS 45's.
Thanks for the great post, and all you share with us! Good news is that the circuit sounds great! Really interesting insight on the tube quality issues. Imagine owning ARC gear and having to replace 12 at a time…. Question - I thought it was a typical “hack” to run tubes at less than full dissipation to extend life (and simply rate the power accordingly) - are there any conservative manufacturers that do this in the ordinary course?
…and remember, when it comes to Russian and Chinese manufacturing quality, friends don’t point nuclear weapons at each other. Would be great to see Western Electric expand beyond the 300B (they could lower prices if they sold more tubes).
In a push pull amp, the bias point is going to be much lower than in a single ended amp. It's usually is never over 70% and can be as low as 50% and not impact power. On a single ended amp power is directly tied to the bias point and on both, the bias point will impact the sound of the amp. IMHO cold biased single ended amps sound bad.
@@SkunkieDesignsElectronics thanks so much for that explanation - I really appreciate it
Western Electric makes quality 300B tubes and according to their website is supposedly working on some other tube models also. Of course, a matched pair of WE 300B's are $1,500.
Many years ago I purchased a Russian Lubitel 6x6 Twin Lens reflex camera but found it almost impossible to get it to focus accurately. Luckily it was cheap. I then got a Chinese Seagull 4A-1 Twin Lens Reflex that was so much better than the Lubitel.
I agree, the tube industry has gone to shit and the war in Ukraine killed it... but the quality problems with Soviet tubes were always there. I remember buying some crappy ones (NOS, and with military markings!) in the 2000s.
With good QA the manufacturers would have a hard proof something is wrong, so they'd just break the thermometer rather than cure the illness behind the fever...
Loved the camera rant too.
Ohh for goodness sake Stephe what to say ?? - Im not surprised regarding the tubes but as you rightly say this crap standard of components and tubes somehow needs bringing into line ! unfortunately as your probably aware i do have all the parts and chassis work done to build these - not sure if my 120's are good or like yours ? mine i got 2nd hand and are a few yrs old but hardly any hrs --- please do what you can to find a sensible answer even if the bias has to be dropped with decent speakers like my klipsch chorus 10w se is still very very good - i said in another comment how good these sound in my blueglow amp - original info from tung-sol is they are a safe straight swap for most kt88 amps and they sound superior in the blueglow ------ please at least let people know and release a BOM as i suspect many are into this build already - how you managed to not swear once during this video is remarkable !!! -- im sure knowing you that a decent resolve is on the horizon - maybe a differant output tube and slight re wire ??? -- chin up eh and dont feel you let anyone down - you have not at all -- im happy to finish my build but do need to know regarding the best biasing situation
Chris
Did you once say that these monoblocks could run EL34's? Seems like a nice and basic design that could be adjusted to run other tubes; was that what you were talking about with the socket swap-outs that you mentioned?
Yeah I can play around with that aspect of this project. This was just depressing to hit this road block.
When )a kid, even places like drug stores (that WAS what they were called) all had tube testing machines at the entrance. grandmothers thought nothing of pulling tubes out of radios or TVs and testing them then asking the clerk for a replacement from stock. Given that tubes now survive in our amps, you might consider the viability of designing and building your own tester, then making money having techs mail questionable tubes to you to evaluate, report and return. You likely would have little to no competition, but it would cut into your youtube time.
the tubes could oscillate with no input or output if its an RF oscillation I have had it with 6l6 P-P and 6v6 single ended. its rare but it happens. you have a good high freq scope. I would sniff around with it to see for sure whats going on. its likely what you think that the tubes are crap.
Yeah I'm too stupid to have ever thought to check that....
I had the same with EH tubes,all of them get broke,never tubes for me!
Sad news - I have 6 of these Tung-sol new but some years old, i will build a single output channel and test the same. Is your last scematic valid with voltages ?
Actually 2 years ago i have tested a SE output stage with them but only at max 420V plate voltage, and i could not get much more power than EL34 or KT88 out of them, around 12-14W with acceptable distortion.
500V plate 495 G2 -52V G1 adjust to get 100ma and then try 110ma at the cathode.
Hi, I have now tested 4 KT120 tubes from 2019 and 2020 at high idle current 120mA and at full load 17W output 154 mA current for 20-25 min and i don't see any red plating at all. I use a test setup with the same components in the output stage as you, but 2500 ohm Hammond OPT 1627SEA. Below data from 2 of them. Highest load is over max Watt dissipation for the tube. My input stage is with 6SL7GT and 6SN7GT.
Tube 1 B+ 500V Plate 496V G2 485V G1 -50,5V I cathode 120 mA output 0W Dist 0% - no redplating 20 minutes
Tube 1 B+ 500V Plate 492V G2 475V G1 -50,5V I cathode 156 mA output 17W Dist 3,1% - no redplating 20 minutes
Tube 2 B+ 500V Plate 496V G2 485V G1 -50,5V I cathode 120 mA output 0W Dist 0% - no redplating 20 minutes
Tube 2 B+ 500V Plate 493V G2 473V G1 -50,5V I cathode 154 mA output 17W Dist 4% - no redplating 20 minutes
What about trying a KT150?
I ordered a pair and tried them, same issue one red plated at 100ma, which is way below the rating and the other red plated at 80ma WAY below the rating. I'm returning those.
Bugger they are beautiful amps and wanted to have them for my Urei speakers 🤥 Good luck finding good Tubes
I'm not giving up.
Are you willing to try Shuguang?
Where is a good place to get a pair?
The only place I could find them were either used on the auction site, or from the Chinese Amazon equivalents
Honor is on life support in most of the Western world. If only Japan still built tubes!
You know, I've always wanted to build GM70 monoblocks....hehehe
I wonder if I can drop those 4E27 tube in... Maybe use an external SWPS for the heaters.
Did you get to try KT88’s
Yeah, they work fine biased up pretty hot.
i have the max plate dissipation in my data sheet for KT120 as 66 watts hence why you have a tube tester
And some of these are red plating at 40W..
Yeah, then there's the problem with fake or defective ICs coming out of China. I recently bought some LM4562NA ICs for $7.00 each. They were listed as AUTHENTIC T.I. I chose them over Chinese versions selling for a fraction of that price, out of fear of getting phony junk.
And "fake" Li ion batteries catching fire...
@@SkunkieDesignsElectronics Yeah for sure Stephe! Many more people are gonna lose their lives from those things catching fire. Once they start to burn they get to 2,000°C & provide their own darn oxygen! Hosing with water makes it explode. The fire is unstoppable & basically you just have to wait for the fire to go out by itself.
And people are expected to park 3 or 400 kilos of this stuff in their garages? - & NECESSARILY charge their EV overnight?
That 'Freemantle Highway' cargo ship that burned till it stopped, has or had over 3000 brand new cars on it all now destroyed because of a fire in one of the ev's. They initially lied & said there were only 25 ev's on board, when in fact there were 500.
I still think you did a great job,.
Thank you!
Cool...
I once had a problem with a bias pot on a guitar amplifier it was new
Wish it was that simple :)
Surely a genuine manufacturer would have quality control to maintain their reputation! Today you can’t be sure where components are made, and with a critical device like a tube, it needs to be near perfect ! You must be very disappointed, I know I would be, it’s not like you can go and buy a large quantity of tubes just to fined a couple of good ones!
Can KT88s work? And, yes, there's a lot of BS...I don't even go to the so called audio shows any more.
Yes and I can also set the KT120 tubes at 80ma. It's just gonna be back down close to what something like the BlueGlow KT88 amp produces power wise.
hmm - after eading so many times about how kt120 are a safe swap for kt88 (manufacturer's) words i dropped the kt120 into my blueglow 88 amp - they sounded so much better in there than the 88's - no hot transformers etc they have far more energy in that amp than the 88's im running that ampp with the single ecc85 (ecc865) and with the klipsch chorus i can take the roof of the house = great match !! @@SkunkieDesignsElectronics
With even moderately efficient speakers (90+ spl) why do you need so much power? Let me know if you ever auction them off.
@@SkunkieDesignsElectronics
What a lousey deal, wased time, effort and money. I think might be worthwhile to salvage the iron and other parts and sell them to recoupe some of your money. I built a VTA Dynaco st-70 and am running Genelex KT88's (russian) and I have been lucky so far. Hope I didn't jinx myself.
You can't go wrong with russian tubes
Uh these crappy QC KT120 and KT150 tubes are russian tubes.
@@SkunkieDesignsElectronics and not Chinese imitations? I got burnt on ebay a few years ago ordering them to end up being bootlegged Chinese crap , it took me taking them to show a friend's father and he went to his shop and showed me the little things that was proved not russian but Chinese, they even had russian crylic writing on them , hell look at all the bogus op amps and capacitors out there on the market . What are we supposed to do in these tremulous times with no respect to us consumers.
Also I ended up with fake DALE resistors once ,
The KT150 tubes I just got were from the tube store, I highly doubt they are selling bootleg china tubes.
Yup upscale audio tubes
This is very bad news. We can only hope things improve. Will your suppliers replace them or refund? Tube amp manufacturers ans bigger dealers do buy batches and test and select. Reach out to Upscale Audio. See comments below.
Upscale audio only sells these to people who have purchased an amp from them. That should explain the situation.
A shame. Stick with KT88s for now.
845 or 6550 come to the rescue? Why not?
I personally would not attempt to base my livelihood on a product that is only made in Russia. Seems like you're just painting a target on your forehead and writing "Fuck me" in the bullseye. In Cyrillic letters. However you should definitely have a conversation with Western Electric in Georgia. You might be able to make a good case for them to produce their own superior version of the KT-120, eventually.
That is a good idea. There are a lot of high end amps using KT120 tubes.
@@SkunkieDesignsElectronics I can use some as a trustworthy substitute for very rare and very expensive GE 6550As which are one of two "certified" tube types to use in my mighty Fender 400PS guitar/bass amp. Conservatively rated at 435 watts RMS out of three pairs of 6550s. The most powerful all tube guitar or bass amp ever built on a production basis.
I don't agree is bad quality Russian products. Is the importers looking for the lowest price crap they can bring in and make more money on rejected products
This was going on from when these tubes were introduced. These "rejected products" should never make it out of the factory doors period if they were legit concerned about QC. They should be destroying rejects.
You are dead right Tung Soul KT 120 are shit
The early production ones with the offset getters work fine.
sounds like square waveform problems inside the tube?
Huh? There is no signal at all in them when they are doing this.
@@SkunkieDesignsElectronics I know nothing. lol :)