Do you plan to develop this amp to a commercial product?

in a properly designed amplifier a transformer should clip before the active stages

The 25.5kHz as full power is not just very good but exceptional

hagtech wrote:

I did bandwidth measurements at 1W.  ….  I should plot both 1W and 6W bandwidth responses.

I always feel strangely disturbed when I see people specify SET response from 2Hz to 150kHz. Here is a practice out there to consider SET response not at full power and I cannot imagine if could be more bogus measurement then that.  A response of a SET amplifier must not be measured at fraction of it’s powers. Well, one can measure whatever s/he what but those numbers should be never made public. Measuring a SET at 10% of full power is like proclaiming that a car goes 1000 miles per hour, forgetting to mention that the speedometer was calibrated in a way that each mile has 23 feet.

A lower frequency response is a properly of power and inductance. In a complete SET amp, with already made gap the inductance is fixed and plate current driven through a transformer become a factor. So, there is ONLY ONE way to measure true frequency response of SET amp: found max power into a given load at MF and to see where the SAME POWER will have -3dB at bottom and atop. Usually at the bottom 20Hz -25Hz considered incredibly good numbers; very few amps do it and most of the “cheap” SETs do 30Hz and up. Some of them roll of say at 40Hz and some of them clip at 40Hz… I heard the stores how well reputed and expensive amps were measured at 50-80Hz of full power. BTW, when I was saying the LF channel of Super Milq goes down to 7.5Hz I meant that it was full power, or 3dB less than the max amplitude that amp I capable to develop. In HF for full-range SET the 20Hz -25kHz are very good numbers at fool power…

Well, theoretically, if a person knows that his 8W for instance amp NEVER develop more than 3W to the given load then the 3W might be recognized as a reference frequency response. In reality, a 8W amp, ever driven a very efficient load of 105dB, in order to never go over 3W, the amps should be high-passed somewhere at 500Hz. I would personally would like even to have at least 6-8dB of headroom between the max signal/power an amps get from music and the moment when amp’s power max out.

Jim, the “full power undistorted bandwidth” is the only bandwidth that counts, at least as I understand bandwidth. The 25Hz to 19kHz is it what would expect from a regular SET if do not spend a LOT of money for output transformer. Your amp is not SE amp and I do not know how bandwidth works in PP amps. Theoretically the no gap transformer should be helpful, in bass region but in practice I feel that a use a DC blocking parafeed capacitor overrides the no-gap OPT bass advantages. I am very much not the person who can credibly talk about amplifier topologies but a need a capacitor and transformer in sequence just does not make sense to my view of common sense.

What is actually found interesting to me, Jim, is that you are trying to make an amplifier, using a new to you solutions an active element without very organic incorporating of actual listening assessments in your design process. It is what I am unable to do, in fact I feel that listening evaluation are the only objective measurement that we have…

I feel that listening evaluation are the only objective measurement that we have

hagtech wrote:

You are lucky to be able to bask in such luxury!  It is one thing to build an amp for yourself, constantly tweaking and upgrading.  Quite another to design a machine for public consumption, at which point things like reliability, repeatability, and manufacturability become important.  Hence, you need to understand every inch of a circuit, the voltages and currents, everything.  If listening was the only criteria, then these would not matter.

Yes, sure I understand it, the public consumption machine and a machine for own tailored needs are very different thing. I am very lucky that I do not do audio as business. Still, I was taking about different things – about the decision support and the ways to assess the decision’s rational. This is however totally different subject and we are way too far from the subject of this thread.

Since you use the 5E6P in your amp it would be very interesting with time to hear your observation how this tube ages. The relatively fast life-span is the only one thing that I do not like in this tube. I usually get around a year out of 5E6P driving it at 17mA and 200V. I do not know how much I will get out of 5E6P at 35mA as I use them in the single-stage amps. The 5E6P does not dies in a year and can works for years and years but I feel it is good to replace it after a year. I would wonder to what observation about the 5E6P life-span you will come across. Particularly, since you use that tracer tools I wonder if you will be able to found any objective parameters that would signifies that the 5E6P is ready to go. I measure current and cathode emission – not always objective, unless I keep a log file for each tube and monitor how it ages. It would be cool of I was able to tag the 5E6P with unique numbers…

One more thing, Jim. Looking at your amp I see the driver tube as very short tube, shorter then it should be. I afraid that you do not use 5E6P but 5E6P-E or 5E6P-I. The 5E6P-E is identical tune to the 5E6P but it is slightly shorter. The 5E6P-E is an impulse version of 5E6P-E and it should not be used. The 5E6P-E measures identically to 5E6P but has no good sound.

very short tube, shorter then it should be

I do not remember what I sent to you, since I sent you for measurement perpose then it might be the impulse version of the tube. In the image below are vertical tubes from left to right:

0A2
6E5P-E (smaller)
6E6P-DR (larger)
6E5P (the largest)
0A2

I did have the Déjà vu feelings about it as I felt that we had this conversation in past. Here we go – it was a year ago.

http://www.goodsoundclub.com/GetPost.aspx?PostID=4291

Will the final appearance be similar to the prototype in the picture?

Frank Blöhbaum, from Sweden I believe, have designed for Thorens a preamp that I think the first outside of Russia commercial use my 6E5P tube.

http://www.6moons.com/audioreviews/thorens4/tep3800.html

I do not know if Frank reads this site but if he does then good for him. As I see he used 6E5P as in output stage of pram, debating it with E810F for whatever reasons. I do not know if it was Srajan’s blooper or Mr. Blöhbaum blooper. I doubt that it was Srajan as he brainlessly juts print what he was told by manufactures. The E810F/7788 shell not be even to use in the same sentence as they are tubes for VERY different purposes. The D3a/7721 are far apart but roughly the same tubes as 6E5P and the D3a/7721 and 6E6P are more or less replaceable and have the same pins. I think Srajan was juts confused with too make new words for himself as I doubt that Frank would put the E810F and 6E5P in the same boat.

Anyhow, it is the first commercial use of 6E5P. It is very nice that back in 1996 Victor Khomenko of BAT was told about 6H30P and he made his best to have the price for 6H30P to shoot over the roof. Leaving out of attention of big manufactures the 6E5P still enjoy the dirt cheap price.

I think I do a great service in maintaining the popularity of 6E5P low.  To my knowledge I am the only English-writing person who talks about uniqueness and advantages of 6E5P. Since my extreme anti-DIY attitude and general anti-social mind-set towards to audio Mormonism they do not take my comments serious, in fact I was reported that a manufacture who refused to use 6E5P just because it came from Romy the Cat. It is what I always say – “Good for them and die with you little secret!” (Courtesy to “The Ritz”).

Interesting that Frank Blöhbaum will not be the first commercial amp with 6E5P that west will be hearing. Back to 2000 or 2001 a Russian company NEM (Novosibirsk Electronic Manufacturing)

http://www.shemki.com/schemes.htm

….brought on CES their new amp. It was 300B drive with a single driver that I never knew at that time and it was somthing that ignited my interest.

http://www.shemki.com/schemas/nem300b12.gif

The amp was driving small Acapealla Horns the sound was not there as the people who run the room (Canadian distributor) had no experience with sound. However, it was very auditable that the amp sounded very-very good. BTW, whatever it worth, the NEM won some kind of price at the show, like best sound, or best product. Regardless how unimportant it is but let agree that to be nominated and to win this thing in Vegas without kissing the industry asses and spending zero efforts for self-promotion was an accomplishment. Anyhow, I took a note about 6E5P right there and was wondering to use it to drive my 6C33C in two stages.  The designer on the amp and the NEM director was Sergey Rubtsov. I know that guy and I am not a big fun of him.  He is a Russian chauvinist and I very much hate this type.  At that time the 6E5P were sold for 11c -13c per tube…

Later on taking with Dima I learn that he and Russian designer Alexander Monakov independently discovered “6E5P for Sound” in 1999. Dima was fixing TV equipment and in deflection amp he saw that small tube with 8.5W plate dissipation, 30 time gain when triode and absolutely different internal construction than anything else he ever had seen. He built right the way a little buffers with it, measured it, listened it, got surprised how good it was … the rest is history…

Anyhow, I wish to welcome Frank Blöhbaum and looks like the Thorens to the 6E5P’s proudly-dysfunctional family.

In my post above I have mention that Srajan is in a way a brainless parrot that repeats the heard and has no ability of desire to understand what was the noise about. His comments that 6E5P and E810F are “close electrical” is a good indication how it works: a manufacture passes wind from behind and an idiot-reviewer runs around him and screams “Hurricane!”

Anyhow, mentioning that Thorens used my 6E5P in out stage I think that it would be deceives to truth if I would not correct another factual error that Srajan used in his article as selling point. Here are two paragraphs from Srajan write up:

The output valves' input capacitance is lower than the power amp's Mosfets by a factor of 1000 of course. Far more importantly, their output current is 30mA. And their output impedance 0.67 ohms. That latter is a shockingly low figure for a direct-coupled tube circuit. It means phenomenal drive over even endless interconnects. Or 600-ohm load happiness as active pro monitors present. Yousa! And for the really curious, yes, the 6E5P's close electrical -- but not pin-compatible -- cousin is the E810F which has a higher transconductance but less anode power dissipation. This preamp circuit would be capable of swinging an ungodly max +/- 60V but is naturally limited by the input signal. A standard 2V input signal translates into roughly a voltage swing of 10 (gain is 16dB). That means overkill headroom for true dynamics. And an unconditional incapacity for clipping the output stage. Ever. It's really a power amp wolf in preamp sheep skin. Blöhbaum runs his original TEP 3800 prototype [lower rights] to drive AKG K-1000 headphones with. Those are beastly inefficient and usually coupled speaker-level to amplifiers putting out 10 watts.

"I know you've lived abroad for half your life and are probably only now discovering much of the hifi scene in your native Germany. It might interest you then to know that both German print magazines and arch rivals at that already published reviews on the TEP 3800. Quite out of character, they agreed with each other and rated it among the best if not the best preamp they ever tested. It's good to observe both the Stereo and Stereoplay tests. The Stereoplay test bench delivered a graph of harmonic spectra depending on output amplitude. This graph shows why this preamp is praised for its transparency. There is no change of the relation between each specific harmonic and each other from the low end of just perceptible whispers to ear-cracking levels. The absolute value of distortion is extremely low. The measured figures of Stereo magazine show 0.0002% @ 1V output. Most high-end people believe that such low distortion will end up in anemic, cold, clinical sound. It's remarkable that especially Stereo magazine -- which is known for favoring some voodoo tricks and beliefs -- praised the musicality of the TEP 3800. Also look at the other values like channel separation of 73dB. Stereo measures that at 10kHz! One footnote: The measured output impedance of 56 ohm is for cinch. The XLR has a stunning 0.67 Ohm output impedance. "

Srajan  said that TEP 3800 uses 6E5P in output stage and I do not exactly understand how the 6E5P might be use in direct-coupling with preamp’s load, what would block DC? Does Frank Blöhbaum in this preamp uses a SS follower after 6E5P?  The most important: where is the 0.67 Ohm output impedance came from? It is obviously that 0.67 Ohm is nether 6E5P anode nether 6E5P cathode. With output current of 30mA that Srajan mentioned the 6E5P has a little bit sub 1kOhm on anode, it is very low but it is not even near 0.67R, unless it run a huge feedback. So, praising the 6E5P as out stage for TEP 3800 preamp I need to say that if the preamp do have 0.67 Ohm output impedance then it has absolutely nothing to do with 6E5P. It would be interesting to chat with Frank Blöhbaum about what he did in there. I would particularly be interested to know what he was trying to accomplish by running 6C19P in a copper chimney. However, it looks like via Srajan interpretation it as much plausible as to have a conversation with a porcupine about the Global Warming.

Romy the Cat wrote:

Why do you think I bout a 1000 of them and closed to the rest of my life my interest in driver tubes? Still, the 6E5P should not be measured as a driver but heard as a driver – the beauty in this tube is in its sound. I do not know why it gave to you more power. It is a regular 32-36 times gain, it means with 4V bias you can get a lot of voltage from this tube with no problems. I uselessly drive it with 200V and you might drive it as hot at 6.5W, with 8.5W max but I would not go there. The only concern that I have, since I knew that you will be juts measure them, if I did not send you the 6E5P-E. The 6E5P-E is impulse venison of the tube and although it measures virtually identically but it does not sound as good, it is ¼ smaller as well. BYW, the benefits that you got were so far not the 6E5P advantages but you juts stopped to use absolutely not appropriate tube (7788) to drive your 2a3. John, I am very much not in position to argue with your about tubes but to use 7788 at line voltage as … a driver is absolutely beyond my believe in mankind sincerity… :-) The Cat

Romy the Cat wrote:

Celsius, I think you do not take in your equation the input voltage. If you bias 6E5P with 4.1V then it can pass 4V with no feedback.  Since the tube has under normal circumstances 33 times gain then you have 132V RMS from your driver stage, wish is if I am not mistaken 373ppV.  That is all that 6E5P can do and among the tubes that I have seen that is one of the highest voltage swinging triode that still can handle 8W on plate. If you would like to use other tubes then it would certainly do but I can only comment upon the tubes that I know and tried.

Celsius wrote:

The problem is that my target is drive a 211  as full amp,  and my CD player  give a litle bit more than 1v to grid. What do you think    1V x 33times x 2.8 give 93ppV enought to drive the 211.

Celsius wrote:

I have  a small board negative voltage regulator based in lm337, Does  anybody test to use as Bias fot 6e5p ?

Romy the Cat wrote:

Celsius wrote: The problem is that my target is drive a 211  as full amp,  and my CD player  give a litle bit more than 1v to grid. What do you think    1V x 33times x 2.8 give 93ppV enought to drive the 211.  Well, you need another gain stage. It is not a big deal but it is way outside my expertise with Milq amplifier and then way how 5E5P works. The 5E5P has 4V on grid, so it makes sense to use it with sources that push out much more then 1V. But three stage do not change the phase, I have ready 4P1L with the socket waiting :-)   Celsius wrote: I have  a small board negative voltage regulator based in lm337, Does  anybody test to use as Bias fot 6e5p ?   I do not like the 5E5P sound with fixed bias, cathode bias, or with Milq bias when voltage is coming from anything else then how it done in MIlq. I understand that you can supply 15oV from anything but I in my experiments find that I like the Gas tube with 10uF cap and high resistor before grid. Any other configuration I did not like. It does not mean that you shall not excrement and it is very possible that you will find some configuration that will be even better then what I find. However, I will not be able to consult you about neither method nor result. I do advise to try my method and then trey whatever you want. If you found that your bias pleases you more ten let me know.