Developing audio in Ireland
by Derek Walton

300B Single Ended Triode
Mono Block Amplifier

front front tubes
The Mission Schematic Parts List
Tube Pinout Construction 1 Construction 2
Layout Drawings World Builders 300b Mk2

The Mission

So why do I want to build a tube amp? I want to create an object of passion, that reflects my ethos and has the ability to paint the picture to create my Audio Illusion.... I want to create something that comes from my heart and from within me and flows into it, through my hands and mind. I want it to be an object of desire.

However...isn't there always a "however"....my knowledge of tube topology is very minimal, and with this in mind, I have tried to gather as much...(is there ever enough!)...information as I can from the web over the last year and then from all this, filter though it to arrive at my design and astethic decisions. Keep in mind that this is my first tube amp and there are more definitive and informative sites out there - This is only meant to show how I went about making my first amp in the hope of encouraging others to join the DIY fraternity.

Design Criteria

  • Directly Heated Triode
  • Single-ended 300B
  • Zero Feedback
  • Directly Heated Tube Rectified
  • Monoblock construction
  • Hard wired

Some thoughts....should you decide to accept it...

Amplifiers are engineered backward, that is , from the output terminals to the speaker. All manufacturers start their design in this manner no matter who they are, they used a certain speaker combination when they were designing it and one should always be aware of this when buying a commercial design. If you do not have a pair of reasonably efficient speakers already then that is where you should start first.

Two things that I have learnt is that zero feedback is the only true route for the single-ended addict . Using feedback of an error signal is in itself erroneous ...I mean why should I put an error signal back into the circuit since this will create further errors and additional harmonics of a higher order. These higher order harmonics are more objectionable and audible themselves, despite the fact that the distortion levels are lower with feedback applied. By its nature, the error can never be eliminated...its the ever-decreasing circles thing...you never actually get to the end of it. Now that kind of philosophy does not appeal to me! And secondly, tube rectification is necessary to let the truth of tone breathe through naturally.

As this is my initial foray into tube building, I wanted to go with the K.I.S.S. school of though...( keep it simple stupid!) and the single-ended is as straightforward as you can get. Despite the large number of available circuits that the are are out there, they are by the most part, similar in their topology. I also believe in the "Less is More" way of thinking and less in the way of the audio path the better. In the case of this amp there is only one capacitor in the signal path!

The 300B is one of the most linear amplifying devices ever made, despite the fact that Western Electric introduced this triode in 1935, it still has the absolute power to move hearts and souls.

300B Heater Supply - AC for the heater is preferable from a sonic point of view. But there are also other reasons why AC is preferred to DC.

Directly heated tubes with dull emitters, such as the 300B, which have a barium oxide-coated filament, when subjected to DC can produce an uneven coating of metallic barium - whereas AC heaters will produce an even coating. This uneven coating can lessen emissivity and shorten the life of the tube.

Copyright © 2000 Walton Audio ®(Reg. 1982) Ireland
Derek Walton
4 Tara place,
Co Meath,
Tel/Fax +35318351100