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Old 18th April 2010, 03:57 PM   #1
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Default 6as7 SE OTL

Hey everybody,
I have i speaker 10 Wrms/8 Ohm 94 db/W/m in a backloaded horn type enclosure so,
I want to built an amplifier with 6AS7 OutputTLess about 10 Wrms/8 Ohm or more,Single Ended,
I found lot of schematics but without info about out power or Zout
Heeeeelp

Last edited by spirakos; 18th April 2010 at 04:14 PM.
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Old 18th April 2010, 06:01 PM   #2
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Ok I think about this one but Push Pull
6AS7GA OTL
who knows if works that machine?Any idea?THD=?
Click the image to open in full size.
Αt 8 Ohms watts=?THD here?

Last edited by spirakos; 18th April 2010 at 06:10 PM.
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Old 18th April 2010, 09:59 PM   #3
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Originally Posted by spirakos View Post
I want to built an amplifier with 6AS7 OutputTLess about 10 Wrms/8 Ohm or more,Single Ended
The only way you're going to accomplish this is with Bench's inverted VT topology. Here, here, and here.

Any way you try this is going to require a whole bunch of 6AS7s. VTs just aren't designed to operate as high current, low voltage devices.
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Old 18th April 2010, 11:16 PM   #4
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Quote:
Originally Posted by spirakos View Post
Hey everybody,
I have i speaker 10 Wrms/8 Ohm 94 db/W/m in a backloaded horn type enclosure so,
I want to built an amplifier with 6AS7 OutputTLess about 10 Wrms/8 Ohm or more,Single Ended,
I found lot of schematics but without info about out power or Zout
Heeeeelp
I have seen a number of Japanese designs using choke loaded 6AS7 cathode follower SE output stages, but they are both extremely inefficient and have rather high output impedances - in most cases I would expect more than 20 ohms, and this makes global NFB mandatory IMHO.

A single pair of 6C33 in a futterman style configuration will net you about 20Wrms and an output Z of perhaps 10 - 15 ohms making global NFB a good idea. The Rosenblit 6AS7 based OTL design might be a good place to start. (You could convert to 6C33 if you are ambitious.)

The 6C33 can be an amazing performer in OTL applications and could also be used in an SE OTL if you wanted, a single tube might get you a few watts.

That said I abandoned OTL amps (I was a fan of the circlotron configuration) for DHT SE amplifiers about 12yrs ago, and would recommend this route to anyone with efficient speakers.

I'm not a fan of "inverted operation" and not a big fan of the Futterman either, but it can work quite decently.
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Last edited by kevinkr; 18th April 2010 at 11:20 PM.
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Old 22nd April 2010, 06:35 PM   #5
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I think that i will build this one
Does anyone knows any change ??
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Old 22nd April 2010, 09:09 PM   #6
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Quote:
Originally Posted by spirakos View Post
I think that i will build this one
Does anyone knows any change ??
This whole thing has been covered on this thread:

What tubes for a tube amp?

Scroll down and you will see the schematic.

I have high efficiency speakers too. The fact of the matter is that if you use the setup as seen in the thread, you will be able to use the least amount of tubes possible of any OTL design. With an upside down SE design you will need more power tubes and make less power, with more distortion. Its really not worth it.

I have a tiny pair of amps I use that have just one 6AS7G per channel. You would think that there would be all sorts of problems but they work quite well. My preamp has a similar circuit in it that uses 6SN7s and it can drive the loudspeakers (16 ohms) to a moderate volume as well, with great bass response.

You could also run one pair of 6C33s, a single 6336 or even a pair of 7241s. Each has their strengths and weaknesses.
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Old 23rd April 2010, 01:38 PM   #7
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Originally Posted by atmasphere View Post
I have high efficiency speakers too. The fact of the matter is that if you use the setup as seen in the thread, you will be able to use the least amount of tubes possible of any OTL design. With an upside down SE design you will need more power tubes and make less power, with more distortion. Its really not worth it.

I have a tiny pair of amps I use that have just one 6AS7G per channel. You would think that there would be all sorts of problems but they work quite well. My preamp has a similar circuit in it that uses 6SN7s and it can drive the loudspeakers (16 ohms) to a moderate volume as well, with great bass response.
1)Ok then NO SE..
2)Can you show us these schematics(6AS7G)&(6SN7)?To run a 8Ohm speaker what i need?

Last edited by spirakos; 23rd April 2010 at 01:50 PM.
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Old 23rd April 2010, 07:51 PM   #8
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Any sound or load deference between this , this , and this one?what are the Advantages and disadvantages for each one?
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