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On both of my builds, I started off using some of the best 10-turn pots I could buy in an attempt to avoid some of the problems others have had with using regular pots. Sometimes they blow, often tuning is difficult, stability is a problem & then finding fixed value resistors to match the results at a certain point is time consuming. And of course, you can't leave the pot in-circuit for the COP runs.
An easy solution to all of this is to use a custom-built Decade Resistance Box. I bought a set of "0-9" thumbwheel switches for about $13 each plus tax from SwitchesPlus in Melbourne. It's very quick & easy to solder in a set of 2W, tight tolerance (less than 0.1 ohm variation), surface mount resistors & wire it up very neatly & reliably. Then you can tune right down to one ohm resolution per step & leave it sit there when you're done. No need to power off, take measurements, etc, etc. Everything is already done for you, as the wheel is numbered & it's very compact. You can look up how to build your own decade resistance box online. Some mess about with rotary switches, but the wiring or schematic is still the same.
An easy solution to all of this is to use a custom-built Decade Resistance Box. I bought a set of "0-9" thumbwheel switches for about $13 each plus tax from SwitchesPlus in Melbourne. It's very quick & easy to solder in a set of 2W, tight tolerance (less than 0.1 ohm variation), surface mount resistors & wire it up very neatly & reliably. Then you can tune right down to one ohm resolution per step & leave it sit there when you're done. No need to power off, take measurements, etc, etc. Everything is already done for you, as the wheel is numbered & it's very compact. You can look up how to build your own decade resistance box online. Some mess about with rotary switches, but the wiring or schematic is still the same.
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