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Old 6th April 2008, 04:03 AM   #1
spgjmf is offline spgjmf  United States
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Default first build 6em7 and it works

hi all,
wanted to share my first scratch built tube amp with the list. I have been reading off and on for a bit and last month started to build a 6em7 amp based on Gary Kaufman's design.

I designed an SS power supply and got it within 2 volts of his voltages. Box is 1/2 inch birch ply with a little enlayed detail. Top plate is steel from a computer filler rack panel. All parts are low cost and nothing special. OT are edcor and PS tranny is big hammand 270fx 550ct thing.

The thing sound nice - clear high and a good detailed bass, which I like. very rewarding project, but man building amps requires so many skills, woodworker, metal worker, designer, artist and engineer. very rewarding.

here are some pics - still need to dress wires and clean up a few things inside.

tubes are the best!

Jeff in Oakland CA
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Old 10th April 2008, 03:23 AM   #2
rman is offline rman  Canada
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Hi Jeff.

I built the same amp but with the tube ps. It really does sound
nice doesn't it? I found much different voltage levels by plugging
in different 6em7's. This did not affect the sound as far as I can
tell, but maybe I don't have "golden ears".

I now use it for rear speakers in home theater, and another
6em7 amp of my own design for the front and for music. here is
that circuit.



Wish I could show my creations but I don't have a digital camera.


Cheers. Rolf.
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Old 10th April 2008, 03:29 AM   #3
rman is offline rman  Canada
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Hmm.
what happend to my attachment? I'll try again.
Final version has 390 ohm kathode resistors on output,
500k grid resistors, and 680uf bypass caps.
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Old 10th April 2008, 05:13 PM   #4
palmas is offline palmas  Portugal
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The 6EM7 is one great surprise!
I use it for amplifying/driver and it sounds great, is very tough and has very low impedance. Also is quite cheap.
Just have to match a pair (I bought about 100 to get a few pairs).
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Old 10th April 2008, 10:26 PM   #5
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Hmm... I wonder about using the 6EM7 as a preamp. That low plate resistance is tempting!

mike
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Old 11th April 2008, 03:42 AM   #6
rman is offline rman  Canada
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Hi.

I just hooked up a headphone jack to my Kaufman 6em7 amp.
Never been much into phones before, but it sounds awesome!
Just played Dire Straights first album on vinyl. With speakers the
drums never sounded quite right on this album and I always
thought it might be the amps very low power output. through
phones the drums are much cleaner sounding.

Rolf.
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Old 11th April 2008, 07:42 AM   #7
palmas is offline palmas  Portugal
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You can use it, it's a noiseless tube that souds great.
I'll try it myself (never thought about using it for preamp before you mensioned it, as it is so powerfull...)






Quote:
Originally posted by mashaffer
Hmm... I wonder about using the 6EM7 as a preamp. That low plate resistance is tempting!

mike
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Old 12th April 2008, 02:11 AM   #8
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Real nice... What OPT did you end up with?

This amp was my first attempt at building tube amps also. I've ventured into building many other "simple" types of SE amps but alway come back to this design. Its something about this tube that is magic to my ears. Too bad it outputs so little power...

rman, I'm tempted to try your design since you mentioned that it sounded pretty much the same but with more power. I just never got the time. Someday...

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Old 12th April 2008, 05:05 AM   #9
rman is offline rman  Canada
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Quote:
rman, I'm tempted to try your design since you mentioned that it sounded pretty much the same but with more power.
Cool see thru design. I used Edcor XSE15-8-5k outputs. Since I was Happy with how the first one turned out I used them on the next one again.

The second amp was inspired by John Broskie's arcticle

http://www.tubecad.com/articles_2001...dion_Amplifier

I used Garry kaufman's power supply with a higher voltage transformer, and a second filament transformer so I could reference the tube that has the Cathode follower and the upper output triode, heater to a higher votage.

Jeff, are those the transformers you used too?
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Old 12th April 2008, 08:44 PM   #10
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RMAN
Can't read the values for input plate and cathode follower resisters (eyes getting old!). Very interesting design.
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