6550 (KT88) Shu Guang vs Telefunken vs Vintage JAN Tung Sol Vacuum Tubes in Dynaco Mark III 

Thank you for your comments. Been a while since I have used this device but still have it in good condition. I don't know if I mentioned it in the video, the cables from the amplifier socket to the test jig may introduce instabilities in some amplifiers if the amplifier is swept with a sine wave. I bought ferrite cores to put around the grid an plate wires but never got around to it. Also some small bypass capacitors in the 100 pF range might help quell any parasitic events but for static measurements it is really handy for matching tubes. Stay safe...

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I agree with you. One circuit I am particular familiar with is the McIntosh MA230 amplifier section where there is individual bias adjustment for the output tubes in addition to a dynamic balance of the driving voltage to the output tubes. Both adjustments make a considerable improvement in THD.

I would be happy to share the schematic but I don't think I ever drew one except on scratch paper while building it. I did go to extra trouble to shield the grid wire but I also found out that this test jig is best used only in a static measurement setup. When I used it on a McIntosh MC40, it threw the amplifier into parasitics. I don't remember what happened when I used it on the Dynaco ST-70. I did buy little ferrite beads to put on each wire at the socket to help suppress parasitics but I never got around to putting them on. They might help if you need to use this setup while running dynamic (signal) tests on the amplifiers. As I am sure you know, the commercial bias probe, or whatever they call it, safely measures cathode current and I have found nowhere a test jig to measure screen current which is definitely very important. Once the screen is damaged, the tube performs very poorly and we likely don't know why. Knowing why doesn't help us fix the tube but it might put us on the right track to examine the amplifier and find out why the screens are becoming damaged. The main cause, I have found, is a bad plate connection pin - pin 3 on the 6L6 family of tubes. I suppose that one seems to fail the most because of the heat transferred to it by the plate support lead in the tube. The new tube sockets I have seen are very soft metal and the female pins wallow out the first time a tube is removed and that is definitely going to become a tube-eating-socket.

@@ElPasoTubeAmps Thanks so much for your comprehensive response. Your comments regarding the screen grid are well-noted. The importance of a stable screen grid supply is highly underrated. I am experimenting with separate rails for my screens. For example, I have a great xfrmr that has two secondaries - one @ 300 VAC and the other 260 VAC both capable of 300ma. Using damper diodes (6AU4, 6DE4, 6AX4, etc ) I get a very stable dc supply of 420 vdc (for plate) and 360 vdc (for screen grid). This is textbook perfect. I place a 5W 4.7K resistor in series with the screen to minimize any damage to the screen upon turn-on. My SOVTEK Mig 60 guitar amp made in Russia has separate plate, screen and preamp rails and a dc filament supply! They Russians knew the importance of separate and stable screen and preamp rails! My goal is a stable 300 vdc supply for all tubes regardless of plate voltage. Svetlana recommends only 300 vdc screen supply for their KT88s regardless of plate voltage. And the 807/ 1625 can only withstand 300 vdc screen supply max. Again, thanks so very much for your superb videos and comments.

Hi Ken - they came to me this matched. I doubt they check screen current as I do but it turned out it was matched also. I got them off Ebay (and ordered six more) from a seller named "doukmall".

+Bucyrus Erie12 I recently replaced one of my old soldering stations with a Weller WES51 that I am completely pleased with so I do recommend that one. The 100+ watt soldering guns are always handy to have around for the larger jobs and I have several that I have picked up at estate sales. First order of the day is to stay alive - the second order is to not burn up the components (especially the tubes) by letting them overheat. The screen grid in power tubes are particularly vulnerable. Thanks for you kind word for myself and Doug. I will help in any way I can and I know Doug will also.

+Dr. Arthur D. Kemp Hello, Sir - The four socket tube tester is a home brew test jig that I will send you a link to. The computer is running Pete Millett's software on a HP 8903 audio analyzer. Below is a link to a video on using the 8903 with Pete's software. I have made four videos on the 8903. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-9MWN1sZZMfI.html

+Dr. Arthur D. Kemp Here is a link to the building of the four socket tube tester. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-pIEG6ZqnYwg.html

+ElPaso TubeAmps They are called shoe, gwang. There is another Chinese factory down in Shenzen Province known as Guiguang or Gwee Gwang. The new Telefunken stuff is just relabeled JJ tubes. Sorry, but that is what it is. I have a huge stash of new in the box Tung Sol 6550s, and General Electric 6550As. I picked up a couple dozen German Telefunken EL156s at the same place. The GEs are by far the most consistent. The Chinese are making some amazing stuff lately.

Yes Seth B - The past Chinese 6550's were not good at all. I always replace them with a new set of Tung Sols when I see them installed in Leslie Amplifiers.

I see that Triode Electronics sells a board made by SDS Labs as an upgrade. The style of series electrolytic capacitors is the way to go nowadays. I use twelve, 470 uF @ 450 volts capacitors in series for 39 uF @ 5400 volts in my transmitters and they work great (so far...). Each capacitor needs an equalizing resistor (470K, 2W or something around that value) across each one to make sure the voltage is distributed equally across each capacitor but that is the way everyone does it these days. The oil filled capacitors seem to last an eternity but they are so large and expensive, it seems no one uses them anymore. As a second thought, this SDS Lab board really makes sense as it is so much easier and cheaper to replace the radial mounting capacitors than a metal multi-section can. Good idea in my opinion.

Here is a video on the beginning of the four tube device. I did not have the large meter mounted yet. I also have one on the single tube “bias probe” also. I am very pleased with the four-tube unit. It just makes it all too easy  ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-pIEG6ZqnYwg.html

ElPaso TubeAmps thanks, David, that is quite nice! Are you familiar with the vintage radio test set analyzers?

+Clinton N No, I have not documented any KT120's. I have only personally tested two amps that use four (4) KT120's. It was a new production Dynaco type amp and I am sorry to say, the performance of the amps did not impress me.

Would you possibly do a side by side of some 6550, kt88,kt90, kt120 and kt150. Maybe do a swap in and test. And then adjust the current specs to optimize say a kt 120 and 150 in your MKIII? I think that'd would be real up to date and interesting since so many review those tubes as "won't go back" "more bass, mid bass linear" ect..

+Clinton N Hi Clinton, one of these days I may splurge and purchase some KT120's and KT150's but as of yet, I have never had any to test. I have owned and tested the KT90's and I think they are very nice.

That is exactly what I figured. I can see by the bottle that they are JJ's - Thanks - TubeDepot is a good outfit to do business with. from my experience.

You are right that they are not original, vintage Telefunken tubes. They are re-branded JJ tubes and they are a bit more expensive than most tubes. As I am sure you know, from the very beginning of vacuum tubes, often times GE or RCA or Tung Sol, Amperex, Mullard and the whole manufacturing sector of vacuum tubes, sold to each other and re-branded. When vacuum tubes are manufactured, I suppose because they are such a labor-intensive, hand-made item, they turn out often times with very different operating parameters. The tube manufacturers of yesterday and today certainly go how to "grade" their tubes and they re-brand and sell the first-class tubes at a much higher price than the average tube. Quite honestly, the vintage vacuum tubes made by the companies listed above were a lot of junk back in their day. I am not particularly a fan of the average JJ tubes but I thought I would try these for the reasons stated above. From the very beginning, I tested these new Telefunken branded tubes and was very impressed with the matching of the quad that I purchased. Years later I am still impressed as they perform very well in a McIntosh 275 and other amplifiers. I am not trying to sell anyone Telefunken tubes but I am sure that all tubes are not made and sold the same. This video is just a comparison of the few tubes I have and how they perform in my particular case.

@@ElPasoTubeAmps Hello that was a quick reply. You confirmed what have been stated online then. You should not worry, there's a lot of fake Telefunken tubes around, they even fake the diamond mark in the glass, if it's fake its engraved - it's supposed to be elevated. (Just google 'Fake Telefunken' and anyone will get a lot of hits.) JJ never had any connection to Telefunken though, but Japanese tube makers did! Back in the day there also have been Japanese made tubes sold as genuine Telefunkens - so even 'genuine' ones might not actually have been made in Germany, but should be of the same standard. The real Telefunken exist and the company is found at telefunken.com/ so whatever you got is not just fake but come with a potential copyright issue. As for me, I got my hands on a very well sounding tube with one USA brand. So such exchange of tubes seem to have been done also to the US of A. After some detective work the tube turned out to be made by Matsushita, I recommend those warmly if you're inclined to test some day. :)

@@andersforsgren3806 I enjoy these conversations and try to respond promptly. I like to compare and document components and assemblies just to see if they live up to the hype propagated over the Internet about them. This definitely includes items like vacuum tubes and audio output transformers which I have found that Acrosound, UTC and even the new James transformers do quite well. One of my favorites is the Acrosound transformers. Same is true for tubes. As you know, all of the vintage names are printed on tubes nowadays as I assumed these tube manufacturers/sellers have purchased the copyright from the original owners. I have read stories where entire vacuum tube factories in England have been meticulously disassembled and transported to China and Russia so that tubes could be made as original as possible to the vintage ones. I don't worry so much about fakes as I am confident I will spot them and these new tubes have where they are made, stamped promptly on them. I think the Russians and their groups have made some excellent tubes. Not picking on the Chinese tubes but the Russians ones work very well and in my measurements and subjective opinion are every bit as good, or possibly better in some cases, than the original venerated USA and German made tubes. Overall, I am grateful that there are a bunch of "nuts" like us, in whatever country they are in, that have such a love for this vintage technology of vacuum tubes that they want to continue building them even today. I think it is wonderful that we can still buy new tubes otherwise, there would not be a vacuum tube audio amplifier business as every tube would cost $1000 each. Just my thoughts on it.

That makes perfect sense to me and you are the only one that has ever mentioned this. I have two Dynaco amps, the MK3 and a ST-70 and the ST-70 will just barely, if I keep the input voltage at 120 volts, do the 35W per channel but I have never seen 60 W out of the MK3. Just another 30 volts or so on the plates will probably do the trick but I was not aware of slight differences in the power transformers. On the test bench, using a Variac, the difference between 110 volts AC input and 120 volts input is truly significant in power output and THD. In general, the amplifiers from this era, Fisher, HH Scott, etc, etc most likely would just barely, if indeed, reach their advertised power output so I just put Dynaco in that category - slightly over rating their amplifiers for marketing purposes. The only amplifiers I have ever seen that consistently will deliver more power than the advertised amount is McIntosh and that is true for their tube amps and their transistor amps. Thanks for letting every one know about these power transformers.

@@ElPasoTubeAmps My Friend just tested his Mkiii with the old transformer that has cloth insulation on the wires, text me results. On 120.9 VAC with a 5U4GB he is getting 506V DC , with a GZ34 529V and Solid State 548V. I had built 2 MK3 but with parts I purchased at different times. With the transformer I got from Triode I was getting about 498 volt, my source is 115v. With the transformer I got from Dynakit I was measuring about 469v.

I am pretty sure that China still makes some vacuum tubes. I think Russia makes the majority of them.

I like your first pronunciation better... Thanks :-)

TheDogpa Yep, the little guy you see is one of my helpers and Made in the USA. He is constructed out of really tiny vacuum tubes and works for free :-)) Thanks for you nice comments.

They are made by JJ and Telefunken buys their top of the line and re-brands them just like tube manufacturers did in the USA and England/Holland/Germany/etc. I have some and they are very well balanced and have kept their balance. i do give them high marks.

@@ElPasoTubeAmps Telefunken stopped at 1967

StillHip4AnOldGuy your are worried about the wroooong thing.

I realize the rubber-meets-the-road in the listening test, and I know everyone will agree with that, but trying to compare repeatable performance by how a person thinks it sounds in a listening test is like the political parties of the Democrats and Republicans. No one is going to agree and it just becomes an angry shouting match. Analytical measurements may not be the last work but it is how we share repeatable data and advance in a scientific manner. There certainly does seem to be a few specimens of vintage high-grade USA and English and German tubes that have lasted 50-60+ years that outperform anything made today. But, we should be thankful that there are individuals in China and Russia that have such a passion for this esoteric and vintage technology that they have actually purchased and moved whole factories to their countries and do the best they can to reproduce vacuum tubes for the world. I remember in the early 1960's the price of a 6L6 was about the same price as it is today and in the 1960's that was extremely expensive where people worked for $1.25 per hour. In the 1930's it was easier and cheaper to build input level transformers like UTC is famous for than to build an active circuit using a vacuum tube just to get a voltage gain. Today, those same quality UTC transformers would cost a thousand $$$$ for what cost in the 1930's, $12. I have often wondered of the multi-millions of vacuum tubes made between the 1940's (end of WWII) and probably the end of the 1970's when vacuum tube production in the USA pretty well ceased, what percentage of those tubes still exist today and perform properly. We can still get JAN quality vacuum tubes, as many as we want thanks to our military equipment, in the receiving-tube class for very reasonable prices that we need to maintain equipment like Collins Radio amateur equipment and most vintage audio equipment. I certainly won't be around to see it but I have often wondered what will be selling on Ebay, 50-60 years from now in the 6L6, 6550, KT88, EL34, 12A-7 market that is pumped-up to be the best-of-the-best when, indeed, all of the highest quality tubes of today are gone. My bet is on the Russian tubes. Just my thoughts.

Unless you're buying NOS at ten times the price, you're stuck with tubes from "hoo flung poo" china or russia. Sad to say, those are the two biggest tube polluters. EAT is making tubes by hand now, KT88's and 300B's but they are a hefty $500/tube....

@@GCKelloch Every reproduction GL tube has been a massive disappointment. I have some JJ EL34's now and they sound good. Russians suck at making good current tubes.