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Old 27th December 2006, 01:54 AM   #1
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Default 6EM7 Amp

Anyone ever do anything with a 6EM7, or the cheaper still 13EM7? I heard some buzz about this tube, and was curious if anyone had ever built with it, or listened to one.
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Old 27th December 2006, 04:33 AM   #2
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Yup!

Fred Nachbaur (RIP) made a SET and PP amp with these:
http://dogstar.dantimax.dk/tubestuf/miniblok.htm
http://dogstar.dantimax.dk/tubestuf/mnibl2-1.htm

And I did an OTL headphone amp with it:
http://geek.scorpiorising.ca/HeadphoneAmp.html
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Old 27th December 2006, 12:21 PM   #3
jane is offline jane  Norway
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I build a no feedback parallel push pull 6EA7 some time ago.

Click the image to open in full size.

I use it almost every day in my number two set up. THD is ~2% at 10W but the amp sounds very good. If I had build it again I would have put a little bit more money into the power supply, it runs a bit hot at 250mA. Both the transformer and 5AR4 is pushed to the limit--my contribution to global warming...

http://www.veiset.net/6EM7/

Jan E Veiset
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Old 27th December 2006, 01:09 PM   #4
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I built a test amp with a pair of 6EM7's. It put out about 1.5 watts per channel and sounded nice. I used the $18 Edcor transformers which are a good match for this size amp. You can get full power down to nearly 30 Hz with these transformers. A bigger transformer would cost a lot more for small performance gain, and if you are spending big bucks on the transformer, you are probably not using a $4 tube. I never built a power supply, I just used my bench supply. I ran about 25 different 6EM7 / 6EA7 tubes through the amp to see what they sounded like and how much power / voltage these tubes could take. I also tried some 6DN7's and some 6GL7's through it.


This was one of the experiments I did while searching for a good low cost amplifier design that could be marketed. I eventually settled on a SE design that can use the 6L6GC since I can get Chinese tubes for $6 each and they make 4 X the output power. These also allow many possible power upgrades that are not available with the 6EM7 (bigger tubes, UL or pentode operation).

I only kept the 6EM7 amp together for a few days since it was just an experiment and I already have a good 1.5 WPC amp using 45 tubes and Electra Print transformers. It would be relatively easy to build a low cost amp using the 6EM7, the Edcor OPT and a power supply made with a $14 isolation trasnformer and a $7 filament transformer.

The highly popular Bottlehead S.E.X. amp used the 6DN7 and the 6EM7 was an option.

http://www.bottlehead.com/et/adobespc/S.E.X./SEX.htm
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Old 28th December 2006, 01:16 AM   #5
dmason is offline dmason  United States
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Sweep tubes well implemented are no joke.

www.ramlabs-musicreference.com I have one of these; 13EM7, hand wound OPT, really seriously sweet sounding machine. Roger Modjeski thought enough of these tubes to come up with this. (with alittle prodding by yours truly) and he gets about 3 watts using some voltage doubling circuit I know nothing about. Driver side is ~6SL7-ish and the big side is supposedly electrically identical to 2A3, and sounds as though from a common genetic.

If you google around you will find some interesting variants from Japan. Also, www.audiohobbyist.com has some more circuits and info.

And George, I am looking forward to building your SE. Soon? Best wishes, Dan
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Old 28th December 2006, 02:53 AM   #6
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Quote:
And George, I am looking forward to building your SE. Soon? Best wishes, Dan
I finally got a week off of work, and have been trying to catch up. I have been either chained to my computer at work, or traveling 500 miles during 6 out of the last 8 weekends to move my mother into assisted living. I got about 200 e-mails to answer and 2 SE amps to finish and photograph for the manual. If I don't get called into work it should all be ready in early January.
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Old 28th December 2006, 12:11 PM   #7
dmason is offline dmason  United States
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George,

I know you have been inundated lately, and pulled in various directions. I hope you weather well the storm, and wish you both a happy new year in Lab...

I have been trying to cook up chassis ideas for the SE, and like the idea of the tubes peeking out, James Dean style, like the deHavilland preamps, but through a copper top, with Maple or Cherry sides, and external PSU.www.dehavillandhifi.com something like that. Maybe at the appropriate time we can have a design forum for chassis style to accomodate board design, tube position, etc...

As for the sweep tubes, in my opinion, unless you shoot for something like Roger Modjeski's superb 13Em7, I say the smart money is going to be on George's SimpleSE, with something like EL34 output tubes. Really good transformers, and some nice coupling caps, might push it right over the top.
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Old 28th December 2006, 12:56 PM   #8
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I built the 6EM7 amp while searching for the design that became the SimpleSE. The 6EM7 amp did sound nice but I wanted more than 1.5 or 2 watts. My speakers (and many first amp builders speakers) are 86 db. I went for an amp that could do 6 to 15 watts depending on configuration. If you have speakers that will work on 1.5 watts, then go for it, it does sound good.

Quote:
I have been trying to cook up chassis ideas for the SE, and like the idea of the tubes peeking out, James Dean style, like the deHavilland preamps, but through a copper top, with Maple or Cherry sides, and external PSU
An amp with tubes sticking halfway out through the chassis would be different, and relatively easy to do. With a toroid power transformer the PSU can be under the lid in the same box.

I am doing an amp now for the manual that has the tubes, transformers, and filter cap sticking up through highly polished aluminum diamond plate. Sort of an industrial look. I just wish that I had some chrome plated end bells for the transformers. Maybe I will add that later.
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Old 30th December 2006, 11:05 AM   #9
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Lots to think about from the responses here. I really need more than 2 watts also, which makes the paralell PP look interesting. It seems like I do pretty well with around 6 watts or so. The EM7s I have sitting around are RCAs with the ugly thin bases, which makes the "submerged" tube design appealing as well. Thanks for the ideas and info, Jay
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Old 30th December 2006, 03:38 PM   #10
dmason is offline dmason  United States
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Jay,

6 watts, with reasonably sensitive speakers, or wideband drivers >93db, will give you a substantial amount of smack. Another reason why George's invention makes alot of sense, among several others.
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