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Oddwatt PP EL-84 amplifier


henry4841

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Lately there has been some interest in diy tube amplifiers or kits. There are very few kits available these days for someone who wants to build their own knowing how to solder and follow directions but are not ready to take on building from a schematic quite yet. This guy has a kit that he has been selling for a number of years. 

http://oddwattaudio.com/owpoddwatt.html

I built this amplifier from the schematic that is posted on a diy site many years ago. It is the only PP tube amplifier I have. Not a lot of power, 5 or 6 watts, but supposedly being run in class A. I have never had a problem with it running out of power or clipping with my LaScala's and at times I listen what some say is really loud. Not being able to carry on a conversation. I have found that 5 watts is the sweet spot for me in a tube amplifier. Below is the schematic I built mine from.

http://diyaudioprojects.com/Tubes/EL84-Push-Pull-Tube-Amp/5751-SRPP-EL84-6BQ5-Push-Pull-Valve-Amp-Schematic.png

http://diyaudioprojects.com/Tubes/EL84-Push-Pull-Tube-Amp/EL84-6BQ5-Push-Pull-Valve-Amp-Power-Supply-Schematic.png

The kit offered by Bruce of Oddwatt is built from a board. Priced at $725 I would not call it a bargain build but you would have a nice sounding amplifier with quality parts, not the cheap parts found in the retail Chinese offerings. You could stick out your chest and say I built it myself when company comes. There is a detailed build on basically the same schematic, and a long thread on another forum for this build. 

 http://diyaudioprojects.com/Tubes/EL84-Push-Pull-Tube-Amp/

And another one on a newer build.  

http://diyaudioprojects.com/Tubes/EL84-Mini-Block-Amps/

 

No affiliation, never talked to the guy but I have been well satisfied with a number of his other designs I have built just from schematics. I look forward to seeing what others think of this design, build and cost. 

 

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It has to run Class A because the of the way they bias it with the  CCS at power tube cathodes. I would pull that out since it doesn't work nearly as good as the good old RC cathode bias.

 

EDIT: I had a look at the schematic and it has to run Class A for two reasons, one the CCS at the cathode and two the self split phase inverter will only work in Class A.

 

These days if I am going push pull I want power and so I just go Class AB, it still runs in A at lower powers but you typically get a lot more power if needed. Push pull Class A you are limited to the same power as if you went parallel single ended, so if I want Class A I stick with single ended and if the customer needs inexpensive power push pull Class AB is tough to beat.

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I agree, nothing inherently wrong with A/B if it is biased correctly. With our speakers a well designed A/B amplifier will probably never get out of class A. Being a complete kit someone may want to give this amplifier a true. Beginning builders can appreciate a complete kit. I just saw a NOS Heathkit receiver sell for a lot of money on eBay recently.  Sounds great and I have a lot of amps to compare it too. I honestly do not know how many.  

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The diyaudio.com store sells the kits as well. There is an upgraded kit with Lundahl transformers. There are a number of reviews on this site as well. I glanced over the review by 6 Moons. High praise for this amplifier. https://diyaudiostore.com/collections/kits/products/elekit-tu-8200r-dx-6l6gc-integrated-amplifier-hpa-kit-with-lundahl-transformers?variant=39316249215049

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