CNO Project 2010

First of all a solid American walnut amplifier housing is made. All the following gear in this project will be made of this wood. This pre-amplifier is based on the "Cleo 6" of our national tube amp designer "Dick van de Merwe". I've tried to build a closed cabinet ,mounting the tubes inside the amplifier. The tubes are visible by a smoke colored plexiglas plate, which I routed for exact fitting in the aluminum top plate.

A time, (and money) consuming project...

This project will consist of the following parts;

-A vacuum tube pre-amplifier

-Two seperate vacuum tube mono amplifiers (mirror build)

-A solid walnut made audio table

-A stand mount loudspeaker set (not ready yet)

Below;

The finished pre-amplifier.

Chapter 2 will bring you to some measurements on this amp.

Chapter 2 >>

Below;

A impression on how the vacuum tubes are mounted behind this 6mm thick smoke colored plexiglass window.

From left to right; D3a - 6N30P - D3a - 6X4 - 6X4

Right;

Ofcoarse the micro controlled volume attenuator is also used here, to accomplish a top of the art volume/input control. Solid silver leads are used to connect the attenuator with the WBT input terminals. In front of the attenuator the 2 Siemens oil filled power supply capacitors are seen. Each section seperated from alu panels, to devide the amp into blocks.

Left;

The 2 main transformers, in front the 4 amorfe chokes mounted on a self made aluminum stud panel. The main transformers are mounted on rubber feet to prevent (50Hz) vibrations on the chassis. Behind the main transformers the main power comes into the chassis, and the ventilation sleeves are positioned in the rear alu input panel.

Picture right, the "power switch board" before mounting.

For those who are interested, I have some (empty) PCB's left. Just mail...

Picture left;

The blue transformer indicates the "power switch board" from were the amplifier is switched on/off. It has a regulated 12Vdc regulater on board, and a Sharp solid state relais, to switch main power.

The heart of the pre-amp electronics is located direct on the tube sockets. The picture below is taken from the upside down amplifier, with the frontpanel removed. Thus Audio Note coupling caps are attached to the top panel of the amplifier. All mounting holes on the alu panels are so called "blind holes", and therefore not visible on the other side of the panel. Capacitors used are Auricap, Black Gate, and Audio Note coupling caps (Copper Foil Oil Filled Mylar, with solid silver leads). Resistors used are Allen Bradley 1 Watt Carbon, Kiwame 5 Watt (green ones), and Holco at the tube grid's. All connections are kept as short as possible. The result is a very compact hardwired amplifier stage.

I've made 5 aluminum panels for this pre-amp, knowing front-, rear-, top-, bottom-, and the black anodised cup which contains the 5 tubes. This last panel is after CNC production bend by myself on my hinged bender to transfer it into a enclosure for the tubes. All 5 alu panels are CNC routed by Schaeffer-ag Germany, after I designed them on my PC. Input signal connectors are WBT 0201 series.

It took me quite some effort to find room for all components in a standard housing of approximately 43cm width. Click on the thumpnail left for a high resolution picture of the inside.

The housings are painted by hand, and have 4 layers of semi gloss PU vernis. Edges are routed in a way to remain same dimension of wood thickness all over the cabinet. There will be no mounting screws visible in the front and back alu panels. It cost me quite some time to construct these 3 housings!