The Superior Instruments Co. Model 76 Bridge part 7: Checking the parts from the SICo 76.
Thursday, March 26, 2026 at 10:08:51
Unfortunately, when hitting some of these parts with high heat, it tends to drive them (temporarily) back towards their actual values - especially in the case of carbon resistors where the heat may drive out some of the water the part has collected over the years.
In this case, the manufacturer provided a lot of surplus RN-type components, as the device is mostly WWII surplus. These held up well over the years, and probably were fine to leave in place - had they not been worked over when installed. Carbons…yeah, those probably weren’t anywhere near what they are now due to the 80W iron drying them out. Capacitors, for the most part, were well out of any tolerance, assuming there was a tolerance marked - or even a value marked at all.
Everything except the 68.1KΩ resistor is in this picture. That part was much like the 750KΩ, some small RN-type that I’m not familiar enough with to identify. It’s probably on the floor or behind some other item on my bench, hidden away due to size. Everything else is right here.
How did they test?
Capacitors, for the most part, are well out of anything I’d call tolerance unless you’re -20/+100. Resistors were mostly pretty good, being mil-spec parts. Carbons were probably better than expected because they were hit with a lot of heat - perhaps I’ll set the 820KΩ parts aside and see how they perform in a year.
In the chart, the following notations are used.
RN - Resistor qualified to MIL-R-10509
WW - Wirewound
DB - Dogbone, probably also RN
CC - Carbon Comp
A part of note
There were two weird metal can capacitors in the unit. There was no label on them, any paper label having come off probably sometime before I was on this earth. Placement suggested they were 0.02μF but they didn’t read anything like that:
I hooked it up to my Olson C-R bridge, but didn’t get any eye opening at all. I decided to run leakage and see what it did.
150V, and almost 8mA of leakage? This thing is shot.
Even at 50V, it leaks.
So…whatever these are supposed to be, they aren’t doing it anymore. I’ll toss them in the bin as known leakage test parts.
Next part of this series: https://wereboar.com … -and-final-thoughts/
Previous part of this series: https://wereboar.com … ring-up-the-sico-76/
Wrapup and final thoughts: https://wereboar.com … -and-final-thoughts/