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K-502 DIY Vacuum Tube (Valve) Amplifier Kit

Scott James Bartlett    UK Flag     To email Scott, type out the email address.   Bookmark or share this page with others.


K-502 DIY Vacuum Tube Amplifier Kit

Electronics has been a hobby of mine for years. However, I have only recently sojourned into the exciting realm of audio.

I've built a few gainclone amplifiers just to get my arm in and although they sound great for the money; I lusted after the clean sound of glass.

The main trouble with most valve projects is the cost! After much arguing with the wife, I settled with the K-502 vacuum tube amplifier kit as a Christmas present. I have a fifteen month old son, so all disposable income goes his way (and rightly so).

See the full selection of S-5 Electronics Tube Amplifier Kits for additional information and a list of kit suppliers.

Finished K-502 Tube Amplifier Kit and Enclosure
Photograph 01: Finished K-502 Tube Amplifier Kit and Enclosure

Construction - K-502 Tube Amp Kit

With the K-502 tube amplifier kit is a piece of pine to mount your finished amp, but it's more fun to put it in a box. The case I used was one of Schroff's 19" multipak jobs (they are very pricey, but beautifully done). The transformer bins on top were purchased from an eBay shop.

Schroff 19 inch Enclosure
Photograph 02: Schroff 19 inch Enclosure

To start with I suggest you use the best tools you can find. It is worth trying to find a good second hand solder station from eBay or other such site. A Weller station can be picked up for around £30 and is a superb tool to work with as long as you respect the components you solder! Try to keep the heat applied as short as possible.

I did all my cutting of the enclosure first as I needed to paint it. This is often the hardest part of any amplifier project. So I mounted the transformers on a solid plate then attached this to the grill top.

When having valves pop out the top and your using "ring towers" and a pcb, it's worth noting you must pay special attention to the size of your "rings" as they may not fit the pcb when placed side by side. (I had to put my valve sockets on wire legs to make them fit the rings!) This was a tedious mistake. The wire is pure silver however.

K-502 Tube Amplifier Kit PCB
Photograph 03: K-502 Tube Amplifier Kit PCB

The only changes to the circuit board were to replace the standard 0.22 uF caps with good quality orange drops. I also replaced the volume pot with a stepped attenuator, which does make a huge difference to both sound and control. It's very easy getting caught up in Audiophile obsession and constantly trying to upgrade. In my opinion this, kit is a great sounding amp, so if it ain't broke, why fix it?

Underside of K-502 PCB
Photograph 04: Underside of K-502 PCB

These simple tube amplifier kits make for a great first project, but if you are a beginner please respect electricity. High voltage can kill the foolish hobbyist, so please be careful and only build this kit if you are very confident of your ability!

If, like me, you are going to use a pre-amp, then you can see the back panel is very easy to do with a hand drill and file. (An awesome chip pre-amp can be found at Elliot Sound Products - Project 88, this is an amazing sounding pre-amp). The transformers sit nicely on top and should be put in enclosures. A friend used old biscuit tins for his K-502 amp as his budget was very restricted, so do scavenge.

Rear View K-502 Tube Amp
Photograph 05: Rear View K-502 Tube Amp

As for the lights, I used four super-bright LED's (one for each corner) and a computer case fan with more blue LED's. I used one of Hammonds neat little PCB mount 12 volt PSU to power this and a rocker switch at the front to turn it all on. It looks cool as hell at night!!

Stepped Attenuator and 12V PSU
Photograph 06: Stepped Attenuator and 12V PSU

As the kit is set for North American power, I needed a step-down transformer to reduce the mains to 110V. I had expected some hum from this but luckily it is still very clean sounding!

Step Down Transformer and Cooling Fan
Photograph 07: Step Down Transformer and Cooling Fan

As you can see I mounted most things in the top! I took advantage of the grill top for handy screw holes! So eventually it looked like this:

K-502 Valve Amp Kit and Enclosure
Photograph 08: Inside of Enclosure

For interconnect wire I used shielded silver Teflon, except on the outputs, where I used standard silver tinned speaker wire. The overall cost for this tube amp project with the enclosure and upgrades was twice that of the kits original cost, but it was worth it (I think).

Closure - K-502 Tube Amp Kit

In summary, this was a fun project to build! It looks and sounds great. Try not to get lost in trying to improve on things as most of time, our simple ears cannot detect the change!

I have built my workbench one end of my son's nursery. All you need is some space, some good tools and our imagination; so get building!!!

Workshop / Son's Nursery
Photograph 09: Workshop / Son's Nursery

Thanks to all who contributed!

For more information and other similar valve amplifier kits, see the collection ofS-5 Electronics K-8, K-12, K-16 and K-502 Tube Amplifiers Kits.