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 Post subject: Re: 6EM7 power amp
PostPosted: 07 Dec 2011, 17:04 
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Gio wrote:
Be sure to look into the voltage ratings of the XLR connectors. They may not be rated for 250VDC.

I like layout three. The tubes seem protected by the transformers. Try maximize distance so you don't get excessive heat build-up.

Of course the XLR are not rate 250V but the pins are thick and well spaced so I don't see a problem. I have used this attachment method on a number of amps up to 435V and never had a problem.

I like layout 1 because it spaces the rec. tubes equal distance from each tranni. Room for a switch and fuse holder back right-hand corner too.

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 Post subject: Re: 6EM7 power amp
PostPosted: 07 Dec 2011, 18:49 
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Joined: 23 Jul 2010, 17:03
Posts: 54
Location: North Carolina,USA
I couldnt get a link but go tohttp://www.tubesandmore.com/ and look under "Vacuum Tube Accessories" and then "Tube Bases" and you'll see them.
Latelly I've been using these from Alliedhttp://www.alliedelec.com/search/productdetail.aspx?SKU=5870041 and this coverhttp://www.alliedelec.com/search/productdetail.aspx?SKU=5870045.Sorry theres no pictures so youll have to look them up in the catalogue.Bassically it gives you a male octal plug that is square shaped and a cover that attaches with 4 screws that will plug into any 8 pin octal tube socket.Hope this helps...David

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 Post subject: Re: 6EM7 power amp
PostPosted: 07 Dec 2011, 19:46 
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Joined: 06 Apr 2009, 10:08
Posts: 1707
Location: US Pacific Northwest
Antique Electronic Supply sells plugs, sockets, and covers for the old Leslie Organ cables. These look like this...
Attachment:
P-OH-506-TH.GIF
Attachment:
P-OH-507-TH.GIF
Attachment:
P-OH-508-TH.GIF
They also have (what look like) matching octal plugs like this...
Attachment:
P-SP8-500.GIF
I have no idea if the P-OH-508 covers will mate with the P-SP8-500 octal plugs. You would have to call and ask but they sure look similar.


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 Post subject: Re: 6EM7 power amp
PostPosted: 08 Dec 2011, 00:14 
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http://store.triodestore.com/amphenol.html


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 Post subject: Re: 6EM7 power amp
PostPosted: 16 Dec 2011, 17:05 
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Mark;

I have been reviewing some of your and Qian's comments about this amp and I have two suggestions for the mono block builds. The first is to increase the coupling cap between the 6EM7 stages from 0.02µf to 0.047µf. This will push the lower knee down a little bit. I also suggest going with the Edcor GXSE 10-8-5k instead of the XSEs. (I hope you haven't purchased your OPTs yet.) I believe that these two changes should significantly help clean up the lower end between 30Hz and 100Hz while not affecting the mids that you like so much.

Just a thought. :2c:

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 Post subject: Re: 6EM7 power amp
PostPosted: 04 Jan 2012, 00:36 
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The OPTs finaly came from Edcor for the next Paris build. I was originally going to make a tri-chassis Paris with one chassis for the PS and then two amp chassis. But the 10W Edcors are small enough to fit with the power tranni and two tubes on a small cast Al chassis. The OPTs are to go in a metal case because the are open frame and ugly. No uglys on my watch.

As you can see from the images all the components will fit on the one chassis with the small 5H choke in the base. This will make it an easier and better build. The second lot of 6EM7 tubes are Super Radiotron AWV tubes made in West Germany. I now have USA made Sylvanian and German made tubes. When the amp is complete it will be nice to hear the difference.

Attachment:
Layout_IV.jpg
Attachment:
Layout_IVb.jpg


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 Post subject: Re: 6EM7 power amp
PostPosted: 09 Jan 2012, 22:11 
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Try using cathode feedback throught the Edcors (just route the cathode bypass cap through the secondary to earth) and prepare to be amazed.


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 Post subject: Re: 6EM7 power amp
PostPosted: 09 Jan 2012, 22:32 
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mach1 wrote:
Try using cathode feedback throught the Edcors (just route the cathode bypass cap through the secondary to earth) and prepare to be amazed.

I think you are hinting at a short global feed back loop. Not sure I'll try it but thanks for the suggestion.

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 Post subject: Re: 6EM7 power amp
PostPosted: 10 Jan 2012, 00:10 
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It's actually a short LOCAL feedback loop which improves the performance of the EDCORs significantly. Only takes two minutes to implement. Simply unsolder the earth side of the output tube cathode bypass cap and connect it to the -ve side of the secodary, connect the +ve side of the secondary to earth and you are done. Ignore at your peril.


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 Post subject: Re: 6EM7 power amp
PostPosted: 10 Jan 2012, 01:06 
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Hmmm... 5.8vpeak of feedback against a 34vpeak swing isn't much (-15dBv) but I guess every little bit helps.

What is the problem with the edcors you'd be attempting to fix with this little LFB loop? Is it just an issue with the XSEs?

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