Sidecar Bob submitted a new Project Log:
Restoring my ancient resistor decade box
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Restoring my ancient resistor decade box
This resistor decade box (AKA resistor substitution box) came with the same lot of equipment I bought half a century ago. I have no idea who made it or when but I have always thought it was probably homemade (but if it was it was well done).
BTW: I know where the knob that matches went but I won't be able to get to it for about a week or so.
When I was using it a while ago I noticed that its resistance was approx. 10% high on just about every setting so I opened it up thinking some of the switch contacts were probably dirty (in retrospect, I should have realized it was unlikely that the X10 rotary switch's contacts would have 1-10Ω resistance and the x100 switch's contacts would be 100-1000Ω). When I saw the resistors inside it I started measuring them and nearly every one is close to 10% higher than it should be. I know that carbon composition resistors can drift out of spec over time (one of the reasons you don't often see them these days) but some of these resistors were leaking wax (I've never seen that before except on very old capacitors) and most of them don't have standard colour coded stripes. I wouldn't be surprised if these were WWII surplus mil spec parts (there were still a lot of those in surplus stores in the 1970s). Definitely overdue for replacement with modern resistors.
I looked up power ratings vs size for carbon comp resistors and concluded that they were probably 1 or 2W so I ordered 20 each 2W 1% resistors in 10Ω, 100Ω, 1kΩ, 10kΩ and 100kΩ and put it aside.
The resistors came today and I didn't have another project on the bench so a few minutes after I took the pics above it looked like this.
Once it was apart I cleaned up the case and took it to the garage shop for a fresh coat of paint, then...
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