Russian KT77, British EL34, German EL34, Russian KT66 Harmonic Profiles

I have always believed that the harmonic profile as viewed on the vintage swept-tuned spectrum analyzers like the HP 3580A or the modern day PC based FFT analyzers, gives us an analytical view into, "how things sound" and in the case of this video, documents the nuances between different tubes of the same class. Furthermore, every since I have gotten into spectral analysis, I believe we can analytically capture the nuances between virtually everything we hear from the voice of a child, a woman, a man and even the meow of different cats. Very subtle differences in the harmonic profile can alter the sound significantly. These tubes documented could appeal to different styles of musician depending on their musical creation and volume level. Hope you find it interesting and valuable.

[@leonardpeters3266]

Effective and informative video. This is actually important information for a guitar player. I never thought to do this. And I have an HP3580. Great job.

[@DeadKoby]

That's the interesting thing about tubes.. what sounds accurate, and what sounds good are 2 different things.

[@Keepee66]

Thanks for all your effort! It is truly appreciated.

[@Dukers2300]

You’re back!!! Thank you!

[@oturgator]

Most differences become apparent after 10W but I suspect most people don’t even hit 3W of listening level, or even less. 10W at home listening is crazy, Police involvingly loud.

[@johntempleton6368]

I really enjoyed this demonstration but It's really making my brain work. I'm trying to figure out what variables are changing the harmonic profile at various output levels and between tube types. Is it grid construction, plate construction, materials? One that stands out is when you got what I call a bi-modal distribution in the harmonic profile. You can clearly see 2 harmonic patterns. One for the even order and another for the odd. The even order harmonics follow the reduction slope but the odd order jump way up above the even order and follow their own reduction slope. It's almost like something happened that only effected the odd order harmonics. Wish I had the toys you're workin' with :)

[@ElPasoTubeAmps]

That is really interesting observations you have made. I will have to watch the videos and see what I can gleen from them. Thanks for your comments and analysis.

[@tedcollins4684]

I do enjoy and learn from your videos. Thank you for sharing! My ears were correct👂👍

[@ElPasoTubeAmps]

I just put the KT66 in my stereo Williamson using the UTC LS-57 transformers and now I know what I am (and am not...) hearing.

[@tedcollins4684]

@@ElPasoTubeAmps had a db20df with kt66s in my kitchen/dinning room

[@78awhite]

As always, I get so much out of your videos! A request if I may... I would love it if you would do a video on speaker crossovers and the autotransformers in them. I know you have a nice set of Klipschorns and a lot of people like to upgrade/update crossover networks. Anything you could add to this topic in a video would be appreciated!

[@ElPasoTubeAmps]

Thank you for your kind comments. That is a nice idea - never thought of sweeping speaker crossover networks. I will give it some thought and see how hard it is to pull one out and check that my sweep generator still works properly. 🙂

[@Rickets1911]

6L6 is also a good swap, with just a couple of small modifications (👍)

[@UDX4570PalmSprings-yh1mv]

My Dynaco ST-70's have KT-88's in it, I've never seen EL-34's in a Dynaco, heck I've never seen any tube with "Dynaco" stamped on it. Very interesting, fantastic video as well!

[@ElPasoTubeAmps]

The original ST-70 amplifiers used EL34. I have that model. I am sure these tubes are 50 years old and still working. Actually, back-in-the-day, the European tubes like the Mullards and Telefunkens, etc. were the cheaper tubes... not anymore. 🙂

[@UDX4570PalmSprings-yh1mv]

@@ElPasoTubeAmps I'll be darn, I didn't know that, thank you for your time, your work with tube equipment is stellar and very educational, I appreciate that. Take care!

[@MrTalaue]

@@ElPasoTubeAmps When I built a couple of EL34 amps in the early 60s the Telefunken tubes were the most expensive, all import tubes and other European tubes were more expensive.

[@jonathanknight8251]

I’d love to see the grid current of the British EL34s, monitored with a current probe and a scope, at around 20W.

[@cityslacker6221]

Look at how beautifully clean those kt66 run within their specs. I have said for years that saratov somehow found the kinkless tetrode magic that GEC had. it really started with the black base Saratovs and the Gold Lion’s made some slight changes to the getters and made the plates more like the late KT66s and KT88s. I also wonder if they made some cathode coating changes, because they seem to last as well as the late MOV Osram KT’s. Also, I love those KT-77. they can put out some slamming power. From a HiFi perspective, I can understand your preference for the black plate RCA 6L6’s, but I was always drawn to the KT tubes for my guitar amps. For HiFi these days, I tend to prefer EL84s and 7189’s running around 20 watts with super sensitive speakers for lower volumes.

[@ElPasoTubeAmps]

The new Russian KT77's did a good job and really maxed out the amplifier while running the 5V3 rectifier. Power output will go close to 100 watts with the solid state rectifier. Yep... now that I know what-is-what in the world of KT66 and EL34's harmonic profiles, I have put KT66 back in my Williamson amplifier and love it. As tekies, we are influenced by measurements and the KT66's are nice and clean. As you say, the KT77/EL34 can produce some slamming power but 20 watts from a properly designed and built Williamson amplifier running beam power tubes into efficient speakers is hard to beat. These harmonic profiles affected how I view stereo amplifier playback systems more than I ever expected.

[@markg1051]

Hello and welcome back David, great to see you uploading new videos! Some of my thoughts on this, especially the fact that you are getting largish amount of even order harmonics with a pair of push-pull matched power tubes. I suspect that the unexpected results are due to the input preamp in combination with a concertina phase splitter which are both single ended design and also in combination with differing bias voltages for different power tubes to make them idle at the same 60mA plate/cathode current. As an example the difference in -ve grid bias voltages between EL34 and 6L6 is about 10V with 6L6 being about 10V more negative than EL34, ie -50V. what this means is that the grid of 6L6 will require 10V more than EL34 to reach same amount of output. Mind you this is just my suspicion as I have no way of confirming it due to lack of test gear you have. Would be very interesting to take note of input signal voltages and negative bias voltages required to get the target 60mA plate current for each pair of power tubes at different power outputs. We all know that the single ended design topology will not cancel the even order harmonics. I'm pretty sure that if the signal driving the grids of your power tubes is pure and free of any overtones, that the output will be pretty free of even order component but will show the odds mainly. Look after yourself and stay well.

[@pppp-fy3xg]

love it nice video

[@johndooley2401]

Great as always

[@adam207321]

Damn, quicker turnarround time than a mcdonalds drivethru. You even broke out the KT77 KT66. Yeah i guess what I said on the previous video is partially true I guess. I am going into thinking mode, maybe let you know if I come up with something else

[@hannesgrublinger4238]

Hello, thank you for this video. Is this a Ultralinear Amp? How many Volts do the work with? 60mA looks for me quite high.

[@paulschuessler8477]

Hi there, maybe i can give you a few hints on those EL34s. They were developed by Philips, not as EL34 but as EL60 (Loctal Base). The EL34 hit the market a little later -it's just an EL60 with Octal-Base. Mullard was just a subsidiary of Philips (like Valvo, Mazda and so on), so those Millard's are in fact the same model as those from the other different brands i mentioned above. Besides other things you can easily recognize them on the two relative narrow pairs of slots in the plate. Those nameless "Made in Germany" ones are different if you're looking closer. The Slots i mentioned are a bit wider and the Bulb goes straight in the Socket. Those are Made in Germany, but most likely Eastern Germany -GDR. Those were pretty common here in the west during the 80's, original they should be labeled RFT -and they are very good and reliable tubes. All of them are real penthodes with suppressor grid (of course, Philips invented the Penthode and had the Patent), the original US 6CA7 has beam-plates instead! EI in Yugoslavia back then also made an EL34 (and labeled as such) with beam-plates instead of the suppressor-grid...

[@ElPasoTubeAmps]

That is good information and explains a lot about the preference some have for the EL34 vs the 6CA7. I always assumed they were the same - Thank you - especially about the 6CA7 having beam forming plates will surely make a difference in how they perform. I think I have a few, if I can find them, and it would be interesting to test them next to the genuine EL34 pentode. I will look thru the attic and see. Thanks for your comments.

[@paulschuessler8477]

@@ElPasoTubeAmps To be sure just have a look inside the System, if they have a Suppressor Grid or Beam Plates is easy to see. Sometimes the RCA or Sylvania just imported our normal european EL34 and labeled them with 6CA7. Of course you're right, it's personal taste if someone likes more the Penthodes or the BPT's. For myself i prefer lo/medium mu-triodes in AB2 (with grid current) like the 812 if it's just for fun/partying or -for serious listening- anything as long it's gm is at least say 25000mhos or such and it's connected as cathode follower in PP/A or slight PP/AB... Greez

[@ElPasoTubeAmps]

@@paulschuessler8477 I have a real affinity for the low mu triode also. I have 812 in a push-pull AM transmitter modulated with a pair of 4-125A. I have never built an AF amplifier with the 812 but I bet it could be good with the right OPT. The 300B or the 6B4G is the top-of-the-heap in my opinion as long as 15 watts is enough. The 2A3 with that 2.5 volt filament is usually more than I want to deal with. Whatever I say here is strictly personal preference but SE amplifiers with their large 2nd harmonic and extended profile is charming but I seem to tire of it after a while. Next is the EL34 - In the beginning I like the accentuated highs but they seem to stress my listening experience after a while also. Ultimately, I go back to the trusty 6L6 family off tubes for stereo listening - my favorite being the KT66. To each our own in our listening preferences.

[@paulschuessler8477]

@@ElPasoTubeAmps Hey OM, sounds good! 812s and 211s (especially the latter) are great for AF in AB2, the Knack then is their driver stage. Also having a some transmitters here, one with 811's in the PA and 812's in the Modulator and my (most beloved one) with RS1003 (65W BPT) in the PA and 6CA7's in the Modulator 😂.

[@ElPasoTubeAmps]

@@paulschuessler8477 Wow... do you post any of this magnificent equipment on a QRZ page? I would love to see it. You might like the pictures I have posted of boat anchor equipment - WA4QGA - 73

[@jutukka]

Very nice video. I wish you could compare EL84's as well! 🤓. I many many years ago built an amp in which I used only late 60's NOS RCA 6V6's, but I built adapters and bias control to be able to use EL84's instead, and especially cheap russian 6P14P-EV tubes. It is amazing how big difference there is between 6V6's and EL84's. 6V6's sounded much cleaner, EL84's much dirtier. The differences between all EL84 I tested seemed to be quite small. And for example original NOS Siemens and Telefunken Special/HQ E84L's IMO didn't in guitar amp sound much better than cheap russian tubes.

[@ElPasoTubeAmps]

I have to admit, I have neglected the 6V6. Such a beautiful little tube but like the EL84, it just can't deliver the power I am always looking for.

[@jutukka]

@@ElPasoTubeAmps I fully understand. But believe me or not, late 60's RCA 6V6GT's are second to none.

[@jasonkirkham550]

How are you getting these wonderful mullard el34s ?

[@ElPasoTubeAmps]

I have been at the hobby a long time and run across these jeweles just whenever it happens. Estate sales have been one place where I have found amazing things that most people would not even stop to look at. Good luck in your hunt. I hope you find a full case of NOS Mullards and Genelex... 🙂

[@jasonkirkham550]

@@ElPasoTubeAmps thank you.

[@kensmith895]

Don't these tubes have different gain ( mu ) figures. The EL34 has a mu of around 11, the KT66 mu is around 6. Wouldn't you need account for these differences.

[@ElPasoTubeAmps]

The specs say EL34 has gm=11mA/V and KT88 has gm=11.5mA/V. mu=gm*ra, so for the EL34, mu=0.011*15K=165 and for KT88, mu=.0115*12K=138. That probably has something to do with it but the general consensus is the wire-wound suppressor grid in the EL34 is what makes the major difference from the beam forming plates in the KT88. The beam forming plates of the 6L6 family of tubes is known for smoother and more linear amplification. The KT family of tubes are modifications of the beam forming plates and other parameters in the tube to increase the linearity of the tube. Remember, KT stands for "kinkless tetrode" and is designed to remove some of the "kinks" from the tetrode tube, no to be confused with the kink in cross-over distortion. That is the best I know about it. Hope it makes sense... Below is a description of the kink in tetrodes. The "kink" in a tetrode refers to a nonlinearity in the tube's plate current versus plate voltage curve, which is caused by secondary emissions from the screen grid. In a traditional tetrode, as the plate voltage drops to a certain level, electrons striking the plate can cause additional electrons to be emitted from the plate surface (secondary emissions). These secondary electrons are attracted to the positively charged screen grid, which can cause a sudden rise in current through the tube, leading to instability or a "kink" in the plate current characteristic. This kink appears as a distortion or irregularity in the smooth, linear progression of the plate current as the plate voltage changes. The issue becomes more prominent at lower plate voltages, where the attraction of the secondary electrons to the screen grid is more significant. The KT family of tubes (kinkless tetrodes) addresses this problem by modifying the internal structure to reduce or eliminate these secondary emissions. This is often done by introducing beam-forming plates (as in BPTs) or other geometrical adjustments that better direct the electron flow and minimize the interaction between secondary electrons and the screen grid. By controlling these emissions, KT tubes achieve a smoother plate current curve, which improves overall linearity and reduces distortion.

[@ronjinks8932]

How can you test using the same OT? Shouldn't the primary impendence be "wrong"?

[@jakep8484]

I believe they have the same nominal impedance

[@ElPasoTubeAmps]

If the plate voltage and current are the same, and they are all running AB1, the load should be the same. Also, there is a wide range of impedance values that can be used in output transformers ranging from at least 8K to 3.6K for common values in this power range. This transformer is a 4K primary.

[@therealjustincase]

The author apparently has no understanding of tube circuits. Sad to see people falling for this pseudo science.

[@ronjinks8932]

@@therealjustincase Apparently you are mistaken, and I don't care what you don't do with you alleged brain ...

[@ElPasoTubeAmps]

@@therealjustincase Thank you for your comment. It's clear that you have an advanced understanding of vacuum tubes and harmonic analysis. I’m fortunate to have a community of sophisticated and knowledgeable viewers on my channel who appreciate in-depth discussions. I’m sure many, including myself, would welcome the opportunity to learn from your expertise. If you have the time, perhaps you could consider creating and sharing some videos on vacuum tube characteristics to contribute to the ongoing dialogue here. We’re always eager to learn and grow together.

[@coldfinger459sub0]

All the 2ed harmonics at 1 W on a pair near 100 db efficiency speakers 🔊 for a push pull Would like to hear the same tubes on 100% class A amp

[@Steven-pv1xr]

FYI. ALL DYNACO ST 70s CAME WITH EL34s. NOT KT88s