EL34 vs 6L6 for HiFi - diyAudio
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Old 4th March 2011, 07:29 AM   #1
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Default EL34 vs 6L6 for HiFi

I know, there must be hundreds of such discussions everywhere, but they all seem to be regarding guitar amps where the interest is in distortion characteristics. I need to know the subjective and the objective differences between the two, especially in SET application.

Any subjective listening opinion on the qualitative differences?

What should I know about the technical differences to build a SET amp around them?

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Old 4th March 2011, 09:23 AM   #2
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I have Winged C EL34 on my SE UL amp with Silk opt comparing to 6p3S-E(6n3C-E in Russian). The EL34s have a more prononuced mid-high, so they are good for pop-rock. While the 6p3s-E(=6L6CG) sound balanced form low to high with good detail and any kind of music is OK.

Some times, more power is needed. A KT88 SEUL is better if you listend to classical music. I have another KT88 SEUL amp with popular James JS6123HS opt. KT88 Gold Lion Reissue is great, but it has nothing close to original GoldLion, so I rename it as Russian Lion. Svetlana KT88 sounds sweeter with bit weaker bass. Shuguang KT88-98 is not bad, sound like Chinese 300Bs.

Anyway, my favorite tube is 6p3s-E. It performs excellecnt in PP UL amp.
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Old 4th March 2011, 12:34 PM   #3
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EL34 was designed with as little curvature as possible, for linearity in
single ended and class A push pull. They cross with a slight wiggle in
class AB, the "Marshall" sound. HiFi amps operating in AB might need
a lot more global feedback to get rid of that wiggle.

6L6 was deliberately curved to cutoff on a square law, optimized for
better linearity in A and AB push pull crossing, "California clean". Most
beam power tubes share this same curve, for same reason. Ex: KT77
replacement for EL34. In SE, 6L6 type requires more feedback than
EL34 type to remove that curvature where it isn't actually helpful.

According to Schade, square law was a feature designed into his G1.
Its not at all clear that every beam power tube or upgraded clone of
his 6L6 will automagically inherit the original curve? I got feeling from
Schade's writings that he could just as easily have made it cutoff like
a normal Pentode if he'd wanted it that way. And if so, may be that
regular pentodes could be designed with square law curvatures too...

I have noticed EL84 pentodes crossing suspiciously smooth in AB.
Looking at XRays of G1, you see the grid coiled tighter at the ends.
Same what I see in 6L6. Though EL84 is not a beam power type.
Except one oddball RCA I have, actually is beam type. Go figure...

In short: For SE, best use EL34. Least curve is what you want.

Last edited by kenpeter; 4th March 2011 at 12:59 PM.
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Old 4th March 2011, 01:05 PM   #4
danzup is offline danzup  Romania
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Do not agree with you after years of listening to SE amplifier diy or factory made.
In short : use 6P3S for best sound in SE and music of different type .

El 34 tend to be very unevenly for some music ....
It is only in my years maybe , but this is what I am hearing when compare .

And 6L6 original (NOS) I will never use but for guitar amplifier !
There are not better tube than 6P3S and 6N2P for my ears !
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Old 20th April 2015, 03:48 AM   #5
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Hi Sprinter, I am a hi-fi listener as the username suggests. I'll be happy to touch on the good questions you raise concerning 6L6 vs EL34 in a SET topology. First I will give some background info.
I decided to get the GC version of the 6L6 to try in my SEUL topology because at a rated 30 watts dissipation it is near identical to an EL34 in this respect. I also thought I might add that I keep plate supply voltage at 400 volts and use fixed bias.
Subjectively speaking, the 6l6GC became the clear winner due to phenomenal detail when compared to EL34 but this was not something that was readily apparent at the beginning. For about a month I been auditioning first one then the other, unable to tell much difference when I stumbled onto to something. That something was that the 6L6GCs gave a beautiful performance with bias set for 40 ma. By comparison the EL34s would sound the same to me set anywhere between 35ma and 60ma.
The technical differences between 6L6GCs and EL34s as far as building around them goes is just about mute. By the time you provide suitable bias adjust range for one you have done it for the other as well.
But there is a technical difference between 6L6 and EL34 that just might tip the balance in favor of the 6l6 in terms of listening quality. Owing to its' beam tetrode design the 6l6 has a far flatter plate current vs plate voltage curve than does an EL34. For more information on this try searching on The National Valve Museum.
In conclusion, you will not go wrong with either tube but for now, for these ears, the 6l6GC is the clear winner. Enjoy!
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Old 20th April 2015, 07:56 AM   #6
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It is false impression to think that the output tube only makes the final performance or sound.
The voltage amplifier/driver stage desing can affect as much.

An example: a triode connected EL34 produces some 5 % of THD.
With suitably designed driver stage the overall THD can vary from some 1 % to 8 %.
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Old 20th April 2015, 10:52 AM   #7
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Kenpeter, the 6L6 is a pentode, KT88 is beam tetrode!
The difference in sound between EL34 and 6L6 is usually down to incorrect bias/load. The anodes have different load impedances and the control grids require a different bias.
Support for Flying Mole Class D, Allen & Heath, Valve amps, older designs & 2CVs. www.jonsnell.co.uk
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Old 20th April 2015, 02:19 PM   #8
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Originally Posted by JonSnell Electronic View Post
The difference in sound between EL34 and 6L6 is usually down to incorrect bias/load.
How can you ever have the same distortion signature with totally different impedance devices, biased totally differently, driving a totally non linear reproduction system, frequency dependent load impedances, non linear speaker core magnetic fields & current dependent speaker coil back EMF?

The whole "validation procedure" is an oxymoron, and makes me laugh.

Vacuum tubes are designed to distort.

They can't do otherwise, which is why most guitar players & SE amp owners love the melodious fuzz, and are deaf.

Last edited by mullered; 20th April 2015 at 02:23 PM.
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Old 20th April 2015, 08:13 PM   #9
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Originally Posted by mullered View Post
Vacuum tubes are designed to distort.

They can't do otherwise
Look at for example 2A3 or 4P1L triode mode curves. Do you think it is hard to get very low distortion from these devices?
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Old 20th April 2015, 08:52 PM   #10
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BJT's and FET's are much more non linear that vacuum tubes.
So has this been a design goal ? I doubt.
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