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Wednesday, March 6, 2013

Low Cost Single Ended 6CB5A Amplifier - Part 2


In part 1 about the low cost 6CB5A mono blocks I already showed the schematic and explained it in detail. In this part I will show the different components and materials which have been chosen for this project.

The photo above shows all the material necessary for one mono block. It contains all the needed parts, including chassis material, connectors, switches, sockets screws and wire.

Let's have a closer look at the various parts. As explained in the previous part, I already had some unused wooden frames which would fit a mono block. These are 30 cm wide, 20.5 cm deep and just 9 cm high. This leaves just 25.5 by 15.5 cm, 8 cm high in the inside. This restricted space led to certain circuit and parts choices since everything had to fit in. Every amp project needs to start with some decisions and the rest has to be adapted to that. In this case it was the available chassis.

A suitable metal plate was designed which can hold all parts. The power transformer is meant to be mounted on top and hidden under a cover. The next photo shows the chassis parts, frame, transformer cover, top and bottom plate:

RCA for the input and banana jacks for the speaker connectors for chassis mounting:

Tubes, plate cap for the 6CB5A and tube sockets, including rubber washers to protect the ceramic from direct metal contact:

The power supply parts: Power transformer including rubber damping elements for mounting, fuse holder and fuse, mains connector with integrated filter, switches for on/off and ground lift:

Material for internal mounting: aluminium profiles, terminal strips, screws, washers, nuts and bolts and the rubber feet for the bottom plate:

The electronic parts: resistors, diodes, capacitors:

The remaining iron: output transformer and B+ choke:

And lastly wire and insulation sleeve, litz wire for mains, heater and B+ wiring, solid core for signals and thicker solid core for speaker out and ground buss:

In part 3 I will show how all this gets assembled.

Best regards



  1. Hi Thomas, great project! Will this be an amplifier for a completely newbie in building up tube amps?

  2. Hi Frank,

    this is the simplest of my amp designs, it is fairly easy to be built. Of course some soldering skills are needed and the necessary precautions when dealing with the high voltages in a tube amp. The parts can be sourced from me, either all of them, or just the iron

    Best regards


  3. This is looking really fantastic so far, great photos and explanations.

    Could you go over your wire gauge size choices and briefly explain why you chose solid core vs stranded. The Litz wire is interesting also and I have never used it.

    I have had a tube amp bread boarded for a long time and have been using it, but, really, figuring out how to neatly package it all up has been more intimidating then building it to start with.

    I struggled for a long while doing searches for the proper types of wire, more explanation would be very helpful. Just figuring out how to cut nice holes in aluminum for tube sockets and transformers takes a while. Your panels are amazing, is the lettering done by silk screening? Nice start!

    Thanks again,

  4. Hi!

    I will explain a bit about the wire in the next part. But it's nothing special really. Wire is not a topic worth to loose sleep about. The litz wire is similar to plain AC zip cord and the solid core wire for signal routing is door bell wire. Some of my thoughts about wire can be found in this post:


    Best regards


    1. Oh yes, I wasn't worried about wire size and type because of sound qualities.

      Mainly I was trying to find the right wire to make easy and good connections to tube sockets and still keep in higher voltages like the B+ etc..

      I was unsure about stranded vs solid though I eventually settled on solid for most of my tube to tube and tube to component interconnects. I like stranded for strain relief properties and flexibility.

      Thanks again and looking forward to reading more about the rest of the construction in the future...

  5. I'll soon be building a stereo version of this amplifier using U.S. sourced (Edcor) transformers. Looking forward to it since I haven't heard a SE triode amplifier for a number of years - I've actually returned to pentodes and ultralinear for less efficient speakers.

    If you ever get the chance, try a SE pentode with a regulated screen and loop (or local) feedback. It's a different sound than the more popular SE triode. Of course I also like pentode drivers!

  6. Thomas,
    This amp design looks great and I'm interested in using 3 of these monoblocks for LCR in a home theater setup. Can you email me prpsc106 at hotmail dot com to discuss.