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Old 23rd July 2007, 03:15 PM   #21
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Hi !
Interesting to see that you achieved a good sound at this operating point. I didn't get good results when operating in the "knee" of the loadline.

Here is the loadline of my 6J5 -follower stage

Click the image to open in full size.

Sound is superb, but ist still a bit high (because of near infinite load, the mu is near to the of the tube)

But there are very few tubes with less available (ECC82 has lots of distortion, no way with that)
So I will try with feedback.

Using a 6SN7/7N7/6CG7/6FQ7/6J5 as cathode follower is a bit supoptimal because it doesn't have a high gm. And output impedance of a CF is 1/gm.

the upper Tube of my -follower is a EL802 with 40mA/V gm. Gives 25Ohms output resistance. At the right you see the 6J5 (A rather rare german one. I have no USA made ones )

Click the image to open in full size.

Regards, Simon
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Old 23rd July 2007, 04:08 PM   #22
ilimzn is offline ilimzn  Croatia
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As small signal amplification tubes go, you almost could not have picked two more different ones.
6SN7 uses high voltages and moderate currents, and is very linear under those conditions.
6DJ8 is a low voltage high GM tube which also happens to have a signifficantly higher mu than the 6SN7, and is great for followers. Without proper RF(like) precautions it is VERY likely to oscilate producing all sorts of audible artifacts. 6DJ8 on 'flying leads' prototypes is unlikely to show it's potential. If you omit the gate damping resistor, it is practically certain to sound bad.
For a line preamp, 6SN7 is already on the top end with it's mu, the 6DJ8 really requires some sort of feedback to get gain down to useful levels in a line preamp - so even there the philosophy of the design would be very different.
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Old 23rd July 2007, 05:21 PM   #23
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Quote:
Originally posted by the_manta
Using a 6SN7/7N7/6CG7/6FQ7/6J5 as cathode follower is a bit supoptimal because it doesn't have a high gm. And output impedance of a CF is 1/gm.
It's only suboptimal when driving finals into Class AB2. Then, if I were doing that, I'd use a MOSFET anyway. The 6SN7 & Co. works just fine as a cathode follower driver to allow for DC coupling to the grids with fixed bias, and to supply enough charging current for the input capacitance, as most audio pentodes really aren't such a difficult load anyway.
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Old 23rd July 2007, 05:34 PM   #24
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Sometimes you need to ignore sweeping generalizations such as "tubes like 6922 are not good for sound". My (very humble) $0.02 is that from my meager experience, both a 6SN7 and 6922... as well as more maligned triodes such as the 12ax7 and the 12at7... can sound fantastic (to my ear) under the right conditions, but the 6SN7 seems to be more forgiving of boneheads like me, in that is sounds good under a wider range of conditions, wheras the other three are rather picky about how you run them and vary more in charactaristics from tube-to-tube, even though can sound just as good if you find a sweet spot to nestle them into.
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Old 23rd July 2007, 07:34 PM   #25
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Quote:
Originally posted by aletheian
Sometimes you need to ignore sweeping generalizations such as "tubes like 6922 are not good for sound". My (very humble) $0.02 is that from my meager experience, both a 6SN7 and 6922... as well as more maligned triodes such as the 12ax7 and the 12at7... can sound fantastic (to my ear) under the right conditions
I always disregard audiophool folk "wisdom"; there's all too much of of that out there. Like right now, my current project is using the very much maligned Tee-Vee t00bz that I can pick up for about $3.00 a pop, and it's sounding mighty fine. Certainly as good as anything that'd use more co$tly audiophool VTs. Put forth a little effort, and you can usually find a good loadline, and/or topology that'll make a bigger selection of VTs sound really good than you might guess. So far, I don't have a need for 12AX7s or 12AT7s, but I wouldn't hesitate to try 'em if I figured they'd get the job done.
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Old 23rd July 2007, 07:54 PM   #26
anatech is offline anatech  Canada
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Hi Miles,
I have some older preamplifiers that use 12AX7's and 12AT7's. They sound better than many newer 6DJ8 type units. What can I say??

I guess the older (real) engineers actually knew what they were doing. I have a world of faith in Morgan Jones also. I will most probably wear his book out before I'm done with it.

-Chris
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Old 23rd July 2007, 08:59 PM   #27
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It seems that a lot of people think that there is one simple solution to all problems, and then report disappointment when this fails to produce the goodies.
I have recently learn't that with certain tubes flying leads of any kind will ruin the sound, this knowledge cleared up a lot of confusion for me. Inattention to detail probably accounts for a lot of those reports of ECC88, and such like, sounding tizzy and harsh. This is a hard lesson that only experience and a good scope can teach.

Shoog
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Old 24th July 2007, 12:01 PM   #28
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my big reason for not using 6SN7s or 6922s is the price! The good NOS stuff has cranked up in value over the years.

Having said that, I've used 6922s for a White Cathode Follower with good results.
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Old 24th July 2007, 02:33 PM   #29
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Default 6sn7 vs E88cc

I agree, many newer components using 6dj8s are poor sounding. ^sn7s are generally 'safer', as described below as it is hard to do anything wrong. But then I would also say it is hard to make it sound the best in the world as well.

Anyway, here is some info for any marketeers and scam artists out there propagating false information.

We have seen the hype, whether DIY or manufacturer, that a design is inferior if the 6sn7 is not used? Has X out there, who teaches such done his homework, or is it to corner the market?

I know one gent who was pushing a particular power tube for years; now he is the "Executive Director - Technology" for a hybrid solid state amplifier company.

Continued, what caps and resistors were used? What were the value of the parts and what design was used?

It is true that the higher the frequency response (figure of merit) a tube can reproduce, the more experience and knowledge is required in designing a good circuit, but the results are better.

Let's take a look at the 6sn7. It is not a bad tube, but neither is it world class tube. It can hardly keep its hf response in a basic circuit. Add even the lowest capacitance Ic and the highs deteriorate (actual listening tests). It is a 'safe' and easy tube to design around, hard to do things wrong.

However, as just about everyone knows by now, the 6sn7 needs some sort of buffer design to support its hf response. So feedback is present, even though localized. But I thought feedback was bad according to another forum?

If one uses two or more stages, with a common power supply, we have a frequency dependent feedback problem from one stage to the others through the power supply. So the sound has been degraded even more.
(Don't let them state they solved it, or it isn't a problem. That is just typical marketing hype. They have a problem, especially with integrated amps.)

As one can see, 6sn7 gainstages have some real problems. Poor frequency response, frequency dependent feedback through the power supply (if two or more actual stages), and negative feedback in the buffer stage.

None of those problems exist when using low Rp, high frequency tubes, including the E88cc.

By the way, be careful of capacitor tests in circuits as well. One used a 0.1 value coupling cap, which cannot possibly be accurate.
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Old 24th July 2007, 05:06 PM   #30
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Default Re: 6sn7 vs E88cc

Hi,

Quote:
Originally posted by Positron
I agree, many newer components using 6dj8s are poor sounding.
Tell me about it

Most likely because they don't throttle them hot enough and end up wasting all that gm.

Though you can get away with running them cool if cathode driven by a pretty good gm tube in cascode.

Cheers!
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