Taras Oleynk aka “ML8” sent me a couple months ago his measurements of different driver line-level tubes including the Melquiades’s diver tubes – the 5E5P. I am posting his data here with his permission, including Taras’ statement that is JUST PRELIMINARY RESULT, and the final testing of DIFFERENT PREAMP TUBES will be available at his site in a near future. (will be posted when available)

Taras used the 6E5P slightly different then it being used in Milq. He has 135V on plate and loads it to 25K. In Melquiades the 6E5P loaded against 15K and has 200V on plate, running 3.4V bias.  Still, I found that the Tara’s measurements are indicative. You will be much surpassed to compare this data with many other drivers’ tubes that Taras have measured and documented in the identical fusion… Also, Taras claims that he have developed a methodology how to interpreter the result in hierarchical manner. It will be very interesting to learn about it future…

The Data File:        http://www.goodsoundclub.com/PDF/6E5P.pdf

The ML8’s Measurements File:       http://www.goodsoundclub.com/Docs/6E5P.xls

The files in Russian and I took liberty to translate it in English where it was necessary.

I think it should be somewhere posted for my and perhaps for others future references. Here is the setting for testing Melquiades' single-stage tubes on Hickok 580/580A tube testers. To test the tube as a driver for a full Milq (two stages) set Bias 3.4V

6E5P and any of its derivatives:

AFHO-BEDO
Plate - J (190V)
Screen -J
Filament 6,3V
Plate Current – Adjust Bias to 30mA
Bias - 2.5-3.4 V
Range - C
Min GM > 16000

6E6P and any of its derivatives:

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… :-)

So what's wrong with the 6SN7, apart from the high prices fetched by good ones?  If building a 2A3 amp for personal use, it seems a likely choice.  I do not know the 6E5P, but I do love the tone of the 6SN7, and I especially like it driving a 2A3, not that I have any use for a 2A3 these days.  For another thing, the 6SN7 is not only capable of amazing grace and delicacy but can be quite "hard" when it called for, and moreover it can pass its qualities right through the 2A3.

Jim, you probably know that George Wright uses a 6SN7 to drive a 2A3 well into A2, which IMO works pretty well in that particular case, especially within the simple Class A envelope, where it seems to "create a sense of headroom" that few 2A3s have with complex material.  Obviously, the downside is truly horrendous distortion at limit...

Best,
Paul S

Paul S wrote:

So what's wrong with the 6SN7, apart from the high prices fetched by good ones?  If building a 2A3 amp for personal use, it seems a likely choice.  I do not know the 6E5P, but I do love the tone of the 6SN7, and I especially like it driving a 2A3, not that I have any use for a 2A3 these days.

Paul S wrote:

Adrian, I agree that SETs generally have issues such as you describe, and moreso the small ones, especially at the frequency extremes, and at saturation, which tends to occur all too soon, IMO.  But I have not sourced these problems back to the 6SN7, or even the 6SN7/2A3 pairing, which I find capable of great contrasts, at least within the all-too-obvious limitations of the small SET.  Are your amps Wright SETs?  I enjoyed my time with those amps, found more to like than dislike, apart from the power limits/struggles with my present speakers.

Romy the Cat wrote:

Sometimes my time will come and some of you will try the 6E5P as a driver, properly used. Then, if this person has a sensitivity and rudimental audio intelligence to recognize some unique 6E5P’s sonic signatures then he will find interested to reread what I have written about the sound of this tube in past. Who, knows, perhaps then the terms like “dynamic viscosity” would sound not so alien for the 6E5P-evolved…

drdna wrote:

Well, and I have a dozen of them sitting here next to my desk while I am building my Milq amp s-l-o-w-l-y so I guess I will discover my audio intelligence level sometime after the New Year.

That is so cool that you Adrian and Jim look like will try to drive with Mil’s input stage the 2A3; I never hear it and I would be very exited if I have change to do so, or at least to hear from other how it was. I would even like people try AD1 instead of 2A3, though the 2A3 is very good tube as well if one have right loudspeaker.

I do not think that I will do it as to me 8W if not here and not there, well, if I move in a much larger room where my single-stage amp will not have enough power (2.5W) then I might consider something like this…

My only concern with all of you guys experimenting with 6E5P-2A3 is that 6E5P is 30-35 time gain tube and 2A3 is relatively low biased tube. Driving with 6E5P-2A3 tandem a 110dB sensitive MF driver is fine but driving with sub 100dB sensitive upperbass driver might be problematic. With moderate 2V on the 6E5P grid the 2A3 dive into class A2 – and it will be very quite frequently or in some cases continues. If you wish then ask Dima to share his “kinky” invention of “coupling capacitor class A2 conditioner”– it might be a useful thing.

Anyhow, please share your thoughts about the 6E5P driver. Do not forget that the milking bias for 6E5P around a grid resistor using Gas tube voltage’s dumping was invited to make the 6E5P to sound right against the 6C33C power triode.  It is possible then other output tube might demand a different biasing application for 6E5P, I have no judgment about it as I did not try other output tube. Here is where you guys come alone…

Here is a document in Swedish language that describes its authors’ view on 6E5P. Since the author extensively use a park of Russian tubes I presume that he is Russian descent.

http://www.romythecat.com/pdf/6E5P_Swedish.pdf

If you do not speak Swedish (I do not) then you might use this tool for semi-comprehendible translation (if you need it)

http://www.systransoft.com/

The document has a number of typical 6E5P applications. Also I am not necessary agree with many of them but it well illustrates the virtuosity of this driver

hagtech wrote:

I run the driver tube at 170V @20mA.  I don't think you need to run this tube at high current.  It is very linear with wide signal swings at this bias.

Good operation points for use it as a driver. You might what to jump voltage to 200-210V and drop current a bit as it will give you higher bias and further up the input stage from a danger of A2.

*** I can get roughly 70Vrms out of it.  Output stage clips first, driver continues with perfect waveforms well into clipping of output. 

Is it the output driver that clips of the output transformer? Looking at the very soft clipping it looks like it was your DTH. Dima taught me that in a properly designed amplifier a transformer should clip before the active stages.

hagtech wrote:

Oh, using transistor constant current source on driver plate.  Output is push/pull parallel SE.  I can set the ratio between single-ended and differential modes via a resistor value.  Suprisingly, best performance was with almost all SE parallel.  I figured more of the differential mode would be needed, as least per WE 93A schematics (their idea). I run the driver through cap to SE/PP interstage tranny.  The tranny is required for my new topology, which has CCS on both output tube cathodes, hence allowing good operation even without matched tubes.  No bias adjustments are necessary, both 2A3 always run at 50mA.  If both working, then voltage across 2A3 is about 235V.  I don't get much power, but this is more of a sonic sweet spot.  Better to give up a watt or two.  Output stage continues to run even if one of the 2A3 is pulled.

Jim, I certainly have no qualifications to be critical in what you do from a technical perspective but from point of a common sense, that I definitely possess, I am very skeptical about what you are trying to do. I am critical not about YOU do but about the entire objectives of the type amps that you are trying to build. Let presume that sound of amp is coming from the gain/driver stage (you might degree but it is my debatable position). If so, then the output stage is necessary primary to develop current. People do not use high efficiency load but what to use low power output stages and in order to rectify it they parallel the output stages, defeating the entire idea of SET purity. With a prober driver and properly used output stage it is very possible that output stage does not matter. What matters is a correspondence of the output stage to the load demands. If so, then why instead of going for push/pull, phase splitter and other unnecessary inventions juts do not take more capable current driver, or in other word to get more powerful tube? The 2A3 might be a nice tube but what are you planning to drive with 3W? Some kind MF channel with sensitivity over 106dB?

hagtech wrote:

All heaters are AC (I think DC is bad for a DHT).  Output noise is 0.16mV A-weighted.  Measurements are with the cheap Sovteks.

… and I wish that everyone do the same. The DC on heaters must not be used for power amps. I was pissed when I saw Lamm ML3 used DC on heaters… Talking about the smelling roses in gas masks…

hagtech wrote:

The main drawback of this design is a low damping factor.  Output impedance from the 9 ohm tap is 3.5 ohms.  That's pretty dang high.  It is because the rp of 2A3 at this bias is about 1k ohms.  It is not the most powerful output tube.  More elegant than robust.

The damping factor? What  do you what: you use a low power tube with huge plate impedance. This thing, from my point of view, should not drive anything under 1000Hz, unless you listen it in a closet with over 105dB sensitivity.

hagtech wrote:

At the moment, my listening setup is in total disarray.  I sold everything I had and am starting over…

Too bad, if you have a stable playback then I'll propose you to use a simplified Milq biasing model and then to pay attention to what happened to sound.

hagtech wrote:

Oh, bandwidth is 6Hz to 25.5kHz.  Not very high, and this is purely a limitation of my interstage tranny.

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.