5_decade_resistorbox

This is a 5 decade resistance substitution box. The main specs are the following

• 10Ohms - 999.990kOhms in 10Ohms steps
• 2Watts power capability
• 0.3Amper maximum current, limited by switches
• 200V maximum voltage
• +-1%+0.8Ohm from absolute value, 50ppm/°C

Even if the resistors are 4W rated, testing shows problems with disipation when a single resistor must disipate all the power.

Some improvements that could be done with little effort:

1. Change resistors pattern to give more power capability to 10' and 20' resistors.
2. Select better rotary switches to give more current capability and better resistance tolerance.
3. Improve disipation by adding a copper plane, or using an aluminum substrate. 

The enclosure is a model PB65 from Chillemi, an injection molding company from Argentina. It cost around 20USD. Don't know if there is a international replacement.

The binding post are the cheapest from aliexpress, the knobs are 3D printed and so is the front panel. The front panel labels were done using a stencil and spray paint.