6N2P-EV VS 12AX7 - What about gain ? -- [SOLVED]

[kagliostro]

Reading in the web often 6N2P-EV tubes are defined as to have a gain slightly higher than the 12AX7 tube, 110 instead of 100

but in Wikipedia http://en.wikipedia.org/wiki/6N2P the gain of a 6N2P tube is defined as lower than the 12AX7 tube and the

6N2P-EV is compared to the 5751WA tube

So .... the 6N2P-EV is a higher or lower gain tube respect to the 12AX7 tube ?

In the datasheet there is plenty of data and curves, but I'm still not able to understand at 100% datasheets

12ax7 datasheet:
http://www.mif.pg.gda.pl/homepages/frank/sheets/093/1/12AX7.pdf


6N2P datasheet
http://www.tubes.ru/techinfo/HiFiAudio/6n2pev.html

http://www.mif.pg.gda.pl/homepages/frank/sheets/112/6/6N2PEV.pdf

http://www.mif.pg.gda.pl/homepages/frank/sheets/113/6/6N2P.pdf

From a vendor I've find indications saying that the gain is 85-115 and this confuses me more ( )

http://www.sovtube.com/en/tubes/277-6n2p-ev.html

Thanks

K

[jazbo8]

It's not that meaningful to look at the amplification spec alone, without knowing the load it has to drive and the input sensitivity needed, hope it does not confuse you even more... 

[kagliostro]

Thanks for the answer Jazbo8


I think that the 100 gain factor universally referred to the 12AX7 tubes is the max gain factor this tube can reach


so my question is if the 6N2P-EV tube may be considered to have the same gain factor, a higher gain factor or a lower gain factor compared to the 100 gain factor of a 12AX7 tube

EDIT: I've find the answer, the gain is 100 +/- 15%, The datasheet was not well passed on scan and I missed the info 

K

[shooter]

I was looking into the 6N2 on audiophile pages n they seem to like it better than a 12ax7, their reasoning, the ax7 was "too gainy".  They didn't talk numbers, just what "seemed" better for a given amp.

[HotBluePlates]

I was looking into the 6N2 on audiophile pages ... They didn't talk numbers, just what "seemed" better for a given amp.

Audiophile sites ( with few exceptions) are worse than a waste of time if you need to know anything technical; you won't duplicate someone else's results without everything in your setup being identical to theirs (even then you may disagree with their subjective evaluation).

Reading in the web often 6N2P-EV tubes are defined as to have a gain slightly higher than the 12AX7 tube, 110 instead of 100 but in Wikipedia http://en.wikipedia.org/wiki/6N2P the gain of a 6N2P tube is defined as lower than the 12AX7  ...

... my question is if the 6N2P-EV tube may be considered to have the same gain factor, a higher gain factor or a lower gain factor compared to the 100 gain factor of a 12AX7 tube ...

Amplification factor is not the only thing that dictates gain in-circuit; this should be apparent because a 12AX7 (with an amplification factor of 100) will exhibit a gain of <1 in a cathode follower. So how the tube is used matters.

Additionally, Amplification factor is only 1 of the 3 triode characteristics (the others being transconductance and internal plate resistance). Amplification factor is the characteristic most used for an initial evaluation of voltage amplifier triodes because it is the least-changing characteristic of the 3. See the 1st graph below, and notice that Mu is the most constant as the tube's plate current changes. As plate current rises, transconductance (G_m increases and internal plate resistance r_p decreases. As a result, you will only truly know what behavior a triode will exhibit if you evaluate the triode's characteristics at the operating point of the actual circuit.

Back to gain in-circuit... For a plate-loaded triode, amplification at the plate output is given by:
A = μ * [(R_L / (R_L+r_p)], where

A = Voltage Amplification ("gain at output")
μ = Triode Amplification factor at the operating point
R_L = Plate Load Resistor
r_p = Internal Plate Resistance at the operating point

If you know how to calculate the voltage output of  voltage divider, you will notice "μ" in the equation above looks just like raw voltage input to a voltage divider, while the rest of the equation is showing that the internal and external resistances divide this value up. In plain language, with a given plate load resistor, if the internal plate resistance is made smaller, the result is a greater percentage of the tube's possible gain. If everything else stays the same, making the plate resistor bigger gives more gain.

One way this is done in practice is to increase the plate load resistor of a tube to get more gain. The problem is that with a fixed supply voltage, making the plate load bigger reduces the total voltage across the tube, which decreases tube current and makes internal plate resistance rise (look again at the triode characteristics graph to see this in a 12AX7). So gain may go up, but not as much as you might expect because the rise in internal plate resistance offsets the gain increase.

Another trick is sometimes called a "Mu Follower" where an active plate load is used instead of a plate load resistor. This is usually a transistor or FET constant-current source, whose current does not change with varying voltage. This looks to the tube like a nearly-infinite resistance (Ohm's Law, R = Voltage/Current; if Voltage gets big but Current stays constant, then R appears big), and when you apply that to the equation above then gain at the plate is nearly equal to the tube's μ.

So how about actual voltage amplification for the 12AX7 and 6N2P? Assume the published μ of 100 for each tube is the same (any individual tube might vary above or below this). Assume each tube exactly follows its published curves (any individual tube might vary above or below this). We would pick an operating point (plate voltage, bias voltage) and plot a tangent to the grid voltage curve at the operating point. I did this for the 12AX7 and 6N2P below. The result was that the 6N2P's r_p was lower at 48.4kΩ vs. the 12AX7's 50kΩ.

[HotBluePlates]

For 100kΩ plate load:
A = 100 * [100kΩ / 100kΩ+48.4kΩ) = 67.4 for the 6N2P
A = 100 * [100kΩ / 100kΩ+50kΩ]) = 66.7 for the 12AX7

That's only 1% difference. And you could (and should) argue that I should have used the same plate current for each tube, regardless of the slight bias voltage difference, because the 6N2P had a slightly higher plate current which reduces internal plate resistance. You could further argue that I should have plotted plate load and cathode resistor lines, and found where each tube is going to land in a real-world use. You could argue that any single tube may have higher or lower internal plate resistance, and exhibit more or less gain in-circuit.

I say that on paper, the 6N2P effectively the same as a 12AX7. If you need to know for certain, you should pop each into an amp socket, apply a test signal and measure the output of each at the plate.

You mean Wikipedia could have wrong info? That's impossible...

[kagliostro]

Many Thanks fot the explanation HotBluePlates

I think Doug could implement a function on the forum to seek and save all your post

there would be enough material to be printed a great book for fans of tubes

Thanks again

Franco

[PRR]

The Russians invented several unique tubes.

But I think this one is supposed to be same-as 12AX7. Or as near as any two tubes from different factories ever are.

[tubeswell]

I believe the russians were being more honest on gain expectations.

either that, or back in the tube making heyday, western tube manufacturers may've tended to toss out a bigger number of tubes that didn't rigidly meet their specs as part of their drive for quality control, so they could say 'this tube that we make has an amplification factor of 100' (and that one is 60), and so forth. (if you take seriously what they said on those old Mullard factory staff induction movies)

[kagliostro]

What would your chance of getting a 6n2p-ev to meet the specifications of 85 to 115 gain, probably 90 to 95%

Yes, I agree (90-95% and maybe more) but that is cheating   

K

[HotBluePlates]

I don't know why I bothered to reply to you, when you mostly just troll.

Back to the standard answer.

[Willabe]

Your NOT funny! Why can't you just play nice with the rest of the forum? Your posts almost always go off in another direction BUT not in a helpful way. 

I believe if it weren't for the good nature of the members, mods and our host you'd be long gone by now. 



                  Brad     



   

[sluckey]

One of the moderators believes that within this thread I posted something that was rude and potentially offensive

It ain't just one!

I see you've been busy today. I notice your post count has actually decreased by about 100 since this morning. I know how tedious it can be to delete posts one at a time. Do you need some help?

[EL34]

 drgonzonm

Please be aware that you can be voted off the forum by a majority vote by moderators and me


It seems that the vote would pass right now if I asked for a show of hands