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My EL 84/2A3 Tube Amplifier
(single ended - direct coupled - no negative feedback) von Torsten Eisenberg, Liscannor, Irland 
It all began when I read that German article "Die Musik"/Das neue "Haus der Harmonie" from Michael Methe in the World Wide Web. It touched me deep inside. We had the same experience about audio systems. Years ago…. My first audio system was a simple mono turntable and an old valve radio, which my father had repaired for me. I was 11 or 12 years old that time and I remember exactly - It sounded just fantastic! And this I nearly forgot! Everything I did own after that was a clear step back the way it sounded. Of cause, the high frequencies were clearer, the bass was deeper and more precise, the distortion was lower and, and, and…. But, I didn't feel the music anymore. Whatever system I had, listening to music was always straining after a while. The music was just there and it sounded very good. But it wasn't jumping at me anymore. I missed the voice, the musicality, the liveliness and the emotions. After labelling tube technology as "old fashion stuff" and studying Transistor as a profession, I decided to give that "old fashion" technology one more chance. I got myself a tiny Philips tube amp, restored it to modern standards and build myself a pair of loudspeakers with the famous, high efficiency Saba "green cone" chassis. 
And there it was again - after all these years: Music, just pure music - straight and alive! Speechless and happy I could dip into and let go again. Now this little Philips amp was never HiFi and I thought to myself, if this is sounding so great, how would it sound with a really good tube amp? And that was always my dream: To build my own Amplifier! First I was thinking about a kit with all the components and the chassis, but quickly I came to the conclusion that I always had to make compromises. But one thing was very clear to me: No compromising whatsoever. I wanted the freedom of choice with components, schematics and design. So, DIY was the thing. But how - And what? I did a www research for weeks and finally decided on an output power tube. My favourite became the 2A3, a direct heated Triode from the 1930/1940. 
And then I spotted a direct coupled tube amp schematic in a www audio forum drawn by Michael Wesemann for a member. The simplicity of that schematic was awesome. That was what I wanted. I got into contact with Michael Wesemann via e-mail and this was leading into an inspiring still ongoing e-mail contact. A constructive process developed where we decided on each component (Pre amp tube, rectifier tube, capacitors, resistors, transformer, chokes, output transformers, and wiring) as well as the philosophy of tube amp design. Two statements of Michael, which impressed me deeply, I don't like to keep back. (Translated from German) "…..that's my philosophy of components. These are things I tried and they were sonically satisfying. Whereas sound is superficial. I build tube amplifier because they can procure positive feelings. Which has nothing to do with measurable sonic qualities, It has to do with the inner qualities of an amplifier. I find that a good tube amp can transport the emotions and the power of good music and therefore touch the soul of the listener and strengthen its vital energy….." And "An amplifier is a musical instrument and not a measuring instrument." I knew, that my amp would sound fantastic. At around Christmas 2005 I got the schematic: A EL84 tube (yes, this fantastic sounding power pentode) as a driver, direct coupled to the 2A3 (without a coupling capacitor), tube rectification and the option to operate the EL84 as a triode or pentode. There are only 4 components in the primary signal path: volume potentiometer, driver tube, output tube and output transformer. The sonic performance will greatly benefit from that. 
PDF Version Now I had to find all the components and order them: Caps for the power section: ASC/Angela Polypropylen in Oil (USA). Riken Ohm und Mills resistors (USA). Power transformer (made to my specs.), chokes and output transformer I got from Welter in Germany. Rectifier tubes from USA and England. The cathode foil cap of the 2A3, Alps potentiometer, speaker sockets, Tube sockets, fuses and fuse holders, power switch, power socket, rubber feet, screws, nuts, washers,….. from Germany. The 2A3 are TJ's Full Music, handmade in China, ordered at Jac Musik in Germany. The RFT EL84 I got at e-bay. They sound great. When I got everything, I put all the important bits on a plywood sheet and then decided on the size and the design. 
At the same time I did the chassis design. I designed the top part with all the holes for the tubes, the caps, the transformers and the ventilation slots for the tubes and resistors on my PC. It was then send to the German company "Schaeffer AG" and was precisely laser cut into a 4mm aluminium sheet. The front, back and side panels are 4mm aluminium as well. I got them here in Ireland and drilled the holes for loudspeaker sockets, input sockets, fuse holder, power socket, power switch and volume potentiometer myself. Now I had to actually build the chassis. And this was exactly the thing I was most afraid of. But sometimes I do work for a company nearby which manufactures big LED displays for airports and railways. They build their own aluminium chassis. The managers there like me a d I did hope they would help me with my chassis. And they did. When the chassis top arrived from Germany I couldn't resist placing everything onto and seeing for the first time how my amp would look like. 
Then I drew the markings for the grub screws onto the underside. 
The very next day the grub screws were pressed into the top, the chassis was welded together, sanded and powder coated. Wow, just like that! 
The big moment came closer. Place and solder all components, wire the amp, make sure everything was all right, then again make sure everything was all right and then - with sweaty and trembling hands - power up - for the first time. 
The tube glow is fascinating and very beautiful... And then there was wonderful music coming out of my speakers! All night. I had never experienced such a sound, such wholeness of music- reproduction before. Very light, fast, fluidly, alive with a lot of authority and very musical. And voices, especially woman's - you get goose-flesh. The bass is precise and there is no hum in my high efficiency speakers. With the term "authority" I mean that my amp takes up it's time to produce each tone exactly at the time it actually should be played. I know it sounds weird or inexplicit, but I can't explain it another way. You have to experience it yourself. The amplifier sounds very very musical, I think that's it. 
Any new tube amp will alter the way it sounds in the first 100 to 200 hours of operation. Mine did as well. All the components have to break in and settle. But the sound gets better and better. The EL84 in my amp was first wired as a triode. After 6 weeks I did try pentode and at first of cause it sounded very interesting and new. Switching back to triode after another 6 weeks I could again listen to what fascinated me at the first power on - to me triode sounds more right. In my amplifier the sound stage is not as wide at triode mode, but much deeper. I like triode better. Another sonic improvement I got after I replaced the GZ37 rectifier tube with the direct heated 5R4. I always had about 15 volt too much of B+, so with the bigger voltage drop of the 5R4 I got the exact B+ figure and with that of cause exact bias settings was established and the good sound on top. What else you want? A few weeks ago I finally got my volume knob. A friend in Germany made it out of aluminium for me from a drawing I send him. Now my amplifier is complete. Here is another photo from the backside with all the connections. 
This amp for sure did burst my initial budget by far (the idea with the amp building kit), but today I know that building this amp from scratch was the right decision. The time was right and I was ready for it. I will never ever give away this amplifier. It is now 5 months in operation and it inspires me each time I listen to. I sit in front of it, sometimes with an open mouth and am astonished, I have a grin in my face and again, a shiver is running down my spine… I would be glad to receive some comments from you: t.eis@gmx.net Torsten Eisenberg Liscannor Irland July, 2006 |