DIY KT88 + 6SN7 push-pull Amp / Part 1

In a previous post, I talk about a new amp project. Since this post, I bought several stuffs to build it. But while looking for parts, I talk with several people. And they convince me to build a push-pull instead of a single-end.

So, I got 4 outputs transformers (2 SE and 2 PP), I gonna try the PP first, and if this work great perhaps, I will sell the single transformers or build a second amp.

The main difference between single-end and push-pull, is distortion. In fact, SE produce a lot of harmonics, so a lot of distortion. Beside this is a bad idea for a power amp, this is really what a lot of people call a “real tube sound”. Anyways let’s start with a full featured push-pull, and perhaps came back to a simple SE just for the fun.

The main issue right now, is that push-pull are a lot of more complicated. I mean you can build a simple SE with only a spare components.. this is not the case of a push-pull. For a single channel, I need 2 tubes, 1 bias power-supply, a highly regulated power supply and a phase shifter ..

For the tubes, I decided to use some KT88. In fact, a friend give me a spare matched quad of NOS (plain old) Gold Lion tubes + the needed output transformers so .. This tube are really great for the HIFI. And they look really great !!!

http://jkx.larsen-b.com/photos/TubesAmps/KT88.sized.jpg

For the input stage, I decided to do something not really common. In fact most tube amps use some ECC82 / ECC83 for the input stage. My choice is something little different cause, I want to use some bigger tube. A lot of people say the 6SN7 (or 12SN7) are great for this stuff too. And some high quality power amps tube this, so why not. After looking for a while for a good schematic, and tested severalls stuff, here the one I gonna build:

http://jkx.larsen-b.com/photos/TubesAmps/canal.sized.gif

In the comming (soon I hope), I will describe the schem and the modification I made. Right now, I’m waiting for the power transformer (comming from US take a long time). In a next post, I will post some photos of my input test bench …

Enjoy light ?

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admin February 9th, 2007


2 Responses to “DIY KT88 + 6SN7 push-pull Amp / Part 1”

  1. # Paulon 15 May 2007 at 11:06 pm

    Hello,

    Nice electronics page. I’m also looking into building my first tube amp and have been looking for a good schematics. Could you kindly provide a link to the webpage that have this schematic? This is by far the best-looking schematics I’ve seen. Thanks!!

    ps. if you could, please reply to my email @ paul.p.pan@gmail.com. Thanks again.

    regards,
    Paul

  2. # JohnKon 23 Apr 2008 at 2:45 am

    Hello et Bonjour!
    Perhaps you should look for a simpler bias system to safe cash and simplify things. Cathode bias = No bias adjustment when you swap tubes! I recommend a fender deluxe 5Y3 circuit with cathode bias, there is no fixed voltage supply to the grids, the cathodes are grounded. Substitute rectifier tube with silicon diodes, or switchable recto. Tube rectifier in double-end amp = power supply sag = sustain. Very loud for a hobby amp.
    I’ve built a few SE amps from scratch, but would recommend using an old chassis from a 50’s radio as a good starter project as well. I am planning an amp in an old mono radio phono unit, SE with all transformers in place, $25 at the auction. It will be the amp/record playing computer desk! anyways, good luck and merci pour l’anglais.

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