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-   -   6AS7 OTL (http://www.diyaudio.com/forums/tubes-valves/102756-6as7-otl.html)

croccodillo 30th May 2007 03:15 PM

6as/ Otl
 
Hello,

I have a bunch of 6N13S (6AS7G) tubes, I'm thinikng to realise an OTL amplifier.
What about THIS ? it seems quite critical to me...
Any other good, tested circuit for me?
I have 8 tubes, so I can use 4 of them for each channel.

Ciao,
Giovanni

Klimon 30th May 2007 05:28 PM

There was an elaborate website from an Italian builder with layout diagrams and a treasure of info on this amp, it seems to have been removed from the net though. I've seen this schematic recommended in an old thread on this forum, it seems to be a well-tested and respected older circuit of the OTL guru behind 'Transcendent sound'. Here's another builder: http://www.ptsoundlab.com/tubes/otl/.../6as7gtaga.htm

Simon

Shoog 30th May 2007 06:20 PM

I have so many doubts about balancing that it scares me rigid. 6AS7 are very variable valves.

Shoog

Miles Prower 31st May 2007 01:28 AM

Re: 6as/ Otl
 
Quote:

Originally posted by croccodillo
I have a bunch of 6N13S (6AS7G) tubes, I'm thinikng to realise an OTL amplifier.
What about THIS ? it seems quite critical to me...
Any other good, tested circuit for me?
I have 8 tubes, so I can use 4 of them for each channel.

For hollow state OTLs, you might want to check into the "circlotron" or "inverted Futterman" topologies (the schemo you linked is a straight Futterman). The inverted Futterman has the advantage of having the lowest Zo, and it doesn't require floating power supplies. The circlotron topology has the advantage of being more "poof proof".

For either design, the 6AS7 isn't a bad choice at all, even if the balance between sections isn't quite what it would otherwise be if this type had actually been intended as an audio final (it wasn't: series pass regulator).

See Here for a good overview of OTL design.

tubetvr 31st May 2007 06:01 AM

Quote:

The circlotron topology has the advantage of being more "poof proof".
Where did you get that from? I think it depends more on actual implementation which design is more reliable, e.g Transcendant designs are reported to be very reliable.

For some comparison on different output topologies see here http://members.aol.com/aria3/otlpaper/otlhist.htm

BR Hans

soundbrigade 31st May 2007 07:15 AM

You can get Bruce Rozenblit's book "Audio Reality" för 20 bucks from his company (Audio Reality .
It gives you yet another design.

This design is published in his book Tube Audio Design. Get it and you get the design ideas as well.

Alastair E 3rd June 2007 02:29 PM

Whatever design of OTL you go for, remember to carefully 'Burn-In' the O/P bottles well before you run them in the OTL.

Hans (TubeTVR) has an excellent section on his Website dealing with the 6C33C-B, and advice on burning-in before use and although a different tube the same precautions I think will serve well.... :D

Basically, the recommendation is to run the tubes with heaters only for a couple of days. Other guys recommend also after this to run at a low Plate-Volts, the maximum rated current through the tube but not exceeding the plate dissipation, for a couple of hours, then all will be well when powered up in the OTL....

The only issues I ever had with O/P tubes in my OTL happened when I used a couple of brand-new 'virgin' tubes straight in the OTL, which after half-hour or so arced over and blew fuses--The tubes were alsom damaged when this happened.....:bawling:

The 6AS7/Russian 6C13s has rather fragile cathode-connections that serve as 'fuses' should they arc-over, which then destroys the tube when they fail.--Or so Im told, I may be wrong here though..

As to the choice of topology, that is a rather 'personal' thing often dictated by what parts/transformers/experience you have. My personal choice was the Circlotron, which although hideously complicated the way I did it, as I adapted an already complicated design to use the 6C33C where it originally used the EL509 tube, but it works nicely in my opinion.:rolleyes:

Hans I believe likes the SRPP type design and has had great results and few problems with his:D

max29 14th August 2007 11:31 AM

Schematics of M 60 MK II somewhere to find.

Any one knows because they used to be in a kit form available.


Thanks
Max

Zero Cool 14th August 2007 11:52 PM

I am currently rebuilding an Atma-Sphere prototype amp that uses 8 6AS7G tubes per channel, 4 In parallel per phase. This is a very very early Atma- Proto type. but it runs great sound very good.

I have not seen many Atma schematics anywhere. I dont know how Ralph would feel about posting his schematics online. I will ask him when he gets back in town.


Zc

HollowState 15th August 2007 02:44 AM

"I have not seen many Atma schematics anywhere. I dont know how Ralph would feel about posting his schematics online. I will ask him when he gets back in town."

I was going to attach the schematic I made of the MA-1 in another thread. Since I have no scanner, I photographed it. But in order to see it clearly the file is necessarily big and this site would not accept it's size. Since I have no website of my own, I'd have to use a host like photobucket or something. I may try it later in a different format to see if it works.

As far as sharing it, I have no qualms or problems with doing so. It is not illegal to post it since it is my drawing, not their's. I am not manufacturing the amplifier nor am I profiting from showing my diagram. Also, one needs no special permission to build a clone for their own personal use.

Not wanting to post it out of respect for a friend is perfectly understandable. But I have no relationship with Atma Sphere and owe them no allegiance. Besides, it's an 18 year old design.

In the meantime, I've set my options to accept emails from members. If someone wants a peek, send me a request and I'll send it via email.

Victor


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