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Old 16th February 2010, 08:30 PM   #31
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Quote:
Originally Posted by TheGimp View Post
Wouldn't the 6N6P be a good choice for the output tubes? Works well at low voltage, Good current handeling capacity. Nice plate resistance. Moderate plate dissipation. Nice Linearity.
Gimp -- If the 6N6P does not catch on here - please start a new thread. thx.
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Old 16th February 2010, 08:52 PM   #32
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The 6N6P is a good tube but its a lot of extra work, because you will need about twice as many as you will of 6AS7s.

As I mentioned earlier, you do not need any special speaker protection circuitry, even a fuse, as long as the primary for the output tube B+ is properly fused. For 6 6AS7Gs running at 135V that will be about 2 to 2.5Amps slow. We've been building these things for over 33 years now and if they were eating speakers we'd be in a hurt locker. We *have* seen a few problems; almost all of them have to do with people putting a different power tube type in the sockets of the amps! So eliminating those incidents, overall we have seen one driver damaged in 33 years and 1000s of amps. In that case the cone shattered but the voice coil was fine. So a crowbar or the like seems like overkill to me.
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Old 16th February 2010, 08:58 PM   #33
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Default How bout a 6N6P OTL Headphone amp??

Has anybody done this??
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Old 16th February 2010, 09:04 PM   #34
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Quote:
Originally Posted by moonbird View Post
Has anybody done this??
Yes. But for headphones you can also use the 6SN7, 6BL8 and the like. We make a preamp (the MP-1) that uses a very similar circuit, and not only can it drive headphones but it does quite well driving my 97db loudspeakers. That whole idea that a small amp can't control big woofers? Rubbish. My speakers have two 15" woofers in them. If my preamp can do it, an amp can too
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Old 17th February 2010, 06:45 AM   #35
markusA is offline markusA  Sweden
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atmasphere>Very cool of you to share your schematics. This I think is pretty much exactly what I was asking for.
If one were to half the number of output tubes compared to the commercial version, i.e. only use 4. How would that affect the numbers?
I really like the idea of starting with two and then adding tubes to reach the desired wattage.
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Old 17th February 2010, 01:19 PM   #36
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I'm still curious about the source impedance of these Circlotron circuits. That will very much determine what sorts of speakers could be used without wild frequency response swings.

I've got a column speaker design underway which will have about a 200 ohm nominal impedance- this may be perfect for a 6528-based OTL.
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Old 17th February 2010, 03:20 PM   #37
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Thank you,
Atmasphere for sharing with us.
And also thank you SY, MarkusG maybe we can keep this thread alive and learn rather than the usual thing of OTL threads dwinding to nothing....

Now where is Wavebourn??? His Russian tube knowledge and willingness to wade in where others of us fear is exactly what we need!!!!!
Earth to Wavebourn..... are you there????
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Old 17th February 2010, 06:13 PM   #38
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Markus, running 4 6AS7s per channel seems to be in the 20-25 watt range.

There are several ways to determine output impedance, apparently based on what you believe in. I'm not a fan of what I call the Voltage Paradigm as it tends to lead to the use of negative feedback in a lame attempt to get the amp to look good on paper.

Gentlemen, what looks good on paper has little to do with how we perceive sound. The bench specs measure things that are not important and for the most part ignores the things that are.

So I measure output impedance by seeing what its actual impedance really is. Most techniques used by the Voltage Paradigm are actually putting a number on the servo gain of the feedback loop. Feedback enhances the odd orders used by the human ear/brain system to measure the volume of a sound, if we tamper with that the system will have a false loudness and a brightness. If you want it to sound like real music feedback has to be avoided. Consequently the method of measuring the output impedance looses is value as soon as the feedback is reduced or eliminated.

We have used this formula from the Radiotron:

2Rp/u + 2
where Rp is the plate resistance of all the power tubes in the circuit, as they are in parallel.

In the case of 4 power tubes this comes to 33.75/4 or 8.44 ohms. In practice our measurements come well within 10% of this formula.

If you use the Voltage Paradigm rules the 33.75 ohm value is what you will get. FWIW as I write this I am listening to an amp that only has 3 power tubes per channel, and its driving our test speakers (High Emotion Audio Bellas) quite well. Obviously a high damping factor is not all its been cracked up to be. I think that myth was started to sell the Voltage Paradigm to the public, and they bought it hook line and sinker. We all paid a price for that too but now I'm way too far down the rabbit hole...
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Old 17th February 2010, 06:22 PM   #39
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Quote:
Originally Posted by atmasphere View Post
Markus, running 4 6AS7s per channel seems to be in the 20-25 watt range.

There are several ways to determine output impedance, apparently based on what you believe in. I'm not a fan of what I call the Voltage Paradigm as it tends to lead to the use of negative feedback in a lame attempt to get the amp to look good on paper.

Gentlemen, what looks good on paper has little to do with how we perceive sound. The bench specs measure things that are not important and for the most part ignores the things that are.

So I measure output impedance by seeing what its actual impedance really is. Most techniques used by the Voltage Paradigm are actually putting a number on the servo gain of the feedback loop. Feedback enhances the odd orders used by the human ear/brain system to measure the volume of a sound, if we tamper with that the system will have a false loudness and a brightness. If you want it to sound like real music feedback has to be avoided. Consequently the method of measuring the output impedance looses is value as soon as the feedback is reduced or eliminated.

We have used this formula from the Radiotron:

2Rp/u + 2
where Rp is the plate resistance of all the power tubes in the circuit, as they are in parallel.

In the case of 4 power tubes this comes to 33.75/4 or 8.44 ohms. In practice our measurements come well within 10% of this formula.

If you use the Voltage Paradigm rules the 33.75 ohm value is what you will get. FWIW as I write this I am listening to an amp that only has 3 power tubes per channel, and its driving our test speakers (High Emotion Audio Bellas) quite well. Obviously a high damping factor is not all its been cracked up to be. I think that myth was started to sell the Voltage Paradigm to the public, and they bought it hook line and sinker. We all paid a price for that too but now I'm way too far down the rabbit hole...
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Last edited by tympani1d; 17th February 2010 at 06:29 PM.
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Old 17th February 2010, 06:30 PM   #40
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Personally It doesn't matter to me what the numbers are as long as it sounds good.
However I've always been told that low source and high load impedance is important?
My speakers have 5ohm at the lowest and 16ohm at the highest (I think).
Normally a 8ohm output impedance would put me off but if you say I'll be ok, I'll believe you.

Doesn't this however result in very low efficency?
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