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  Velleman K8020 high-end tube preamplifier. 
  Feb 23, 2006, 08:30am EST 

Vacuum tubes

By: Sander Sassen

Preamplifiers come in all shapes and sizes, it its simplest form a preamplifier is just a potentiometer and input selector with no gain. In all honesty such a preamplifier doesnít quality as one really, as thereís no gain. But obviously thereís a wealth of preamplifiers that do offer a bit of gain and use a variety of concepts. Some use transistors or integrated circuits and others use vacuum tubes. I was looking for a simple preamplifier that would offer me a number of inputs and would allow me to upgrade or improve upon it by simply replacing parts with better ones.

Front K8020 preamplifier

The front of the K8020 preamplifier, featuring push buttons.

I ended up buying Vellemanís K8020 high-end tube preamplifier simply because it met all of my requirements. On top of that it had been over a decade since I last tried my hand at anything that featured vacuum tubes, hence I was looking forward to getting reacquainted with this 1940ís technology. The Velleman didnít disappoint; it comes with a very well made enclosure and decent quality parts that allow for some upgrading along the way. Because I needed a starting point I simply built the preamplifier according to the assembly manual, no changes whatsoever.

Back K8020 preamplifier

The back of the K8020 preamplifier, featuring gold-plated connectors.

The assembly manual is actually very well layed out, if you follow it to the letter I have no doubt anyone will be able to build this preamplifier. It details, step-by-step, what parts to mount onto the printed circuit board and illustrates this with a drawing of what each component looks like. The kit comes supplied with a number of tools already so all you need to get started is a Philips head screwdriver, a pair of needle nose pliers and a nail cutter to cut off the wires of the components after soldering them into their designated locations. Obviously it helps to read through the assembly manual prior to starting construction so you know what goes where.

1. Vacuum tubes
2. Powering it up
3. Some numbers
4. Conclusions

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