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PostPosted: September 16th, 2014, 2:03 pm 
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I have a pair that a friend is wanting to sell me, these are the EV A50 amps, which I can find no real info on as far as sound quality. Seems as though there may be issues with stability, but as far as sound quality, I have nothing to judge these on and as they are not inexpensive, wanted to get some info before considering pulling the trigger... thanks


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PostPosted: September 16th, 2014, 2:32 pm 
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Circlotron amps are terrible. You should sell them to me really cheap. That will save you headaches and Keep your conscience clear.


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PostPosted: September 16th, 2014, 3:18 pm 
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Stuart Polansky wrote:
Circlotron amps are terrible. You should sell them to me really cheap. That will save you headaches and Keep your conscience clear.


I wish I was getting them cheap! So, are these worthwhile to buy and (probably) fix up?


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PostPosted: September 16th, 2014, 3:18 pm 
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I think the Atma-Sphere OTLs use a variation on the circlotron design. No idea how the EVs sound though. If they're not cheap, you could almost certainly build something better for less ;)

Roscoe

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PostPosted: September 16th, 2014, 4:03 pm 
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Roscoe Primrose wrote:
I think the Atma-Sphere OTLs use a variation on the circlotron design. No idea how the EVs sound though. If they're not cheap, you could almost certainly build something better for less ;)

Roscoe

from what I have been able to cobble together, these amps are supposed to have very good freq response and distortion via their design. There is a tread on a diy using the EV A50 as a template, but that diy project is expensive to build, these amps offered to me for $2000 is a bit tight for me right now. I did read that Sound Practices had an article on a diy circlotron, not sure what the verdict was....


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PostPosted: September 16th, 2014, 5:05 pm 
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Okay, clarification here. Roscoe and I were both assuming that this was an OTL design. Not the case; there is an output transformer. The advantage in this circuit may lie in that the output tubes are functioning in cathode follower mode. Cathode followers have very low distortion compared to grounded grid or grounded cathode designs (think degenerative feedback across the cathode resistor). That's the good news. The bad news is that the gain of a transformer coupled output stage in cathode follower mode is going to be way less than unity.

So the demand for gain falls on the input stages. That gain needs to be very large and controlling the distortion there is another problem. Broskie has written on it extensively, I'd read up. Dave Berning has an opinion on the CF output stage as well. Maybe he'll chip in here.....

Personally, at $2k, I'd pass on them. Not even close. If it was an OTL design, I'd have to hear them, because I'm thinking wholesale rebuild with modern parts.

I think collector value and non-DIY users would be interested in this. As for a DIY guy, I COMPLETELY agree with Roscoe....Do It YOURSELF for lots less and a better finished product!!

Stuart


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PostPosted: September 16th, 2014, 5:34 pm 
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Stuart Polansky wrote:
Okay, clarification here. Roscoe and I were both assuming that this was an OTL design. Not the case; there is an output transformer. The advantage in this circuit may lie in that the output tubes are functioning in cathode follower mode. Cathode followers have very low distortion compared to grounded grid or grounded cathode designs (think degenerative feedback across the cathode resistor). That's the good news. The bad news is that the gain of a transformer coupled output stage in cathode follower mode is going to be way less than unity.

So the demand for gain falls on the input stages. That gain needs to be very large and controlling the distortion there is another problem. Broskie has written on it extensively, I'd read up. Dave Berning has an opinion on the CF output stage as well. Maybe he'll chip in here.....

Personally, at $2k, I'd pass on them. Not even close. If it was an OTL design, I'd have to hear them, because I'm thinking wholesale rebuild with modern parts.

I think collector value and non-DIY users would be interested in this. As for a DIY guy, I COMPLETELY agree with Roscoe....Do It YOURSELF for lots less and a better finished product!!

Stuart


Stuart, you have this sussed out correctly, Berning's name did crop up on a discussion in diyaudio as there was a person building a clone of the EV A50 and was asking questions about it. The gist seems to be that you cannot build one for cheap because of the iron, so $2k is probably not a bad deal, but is out of reach for me at this time. I would think that an OTL would be a cheaper build, no output tranny! Oh well, maybe another time, besides, got too many projects I need to get done before taking on another!


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PostPosted: September 17th, 2014, 9:03 am 
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Never built a clone of the A50. The only things I built similar were OTL high-voltage output stages for a variety of uses, including electrostats using 807s.

David


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PostPosted: September 17th, 2014, 9:16 am 
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David,

We did speak about your opinion of Circlotron designs and cathode follower output stages some time back. I remember you mentioned having dabbled in CF design, but ultimately going other directions......

Stuart


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