An EICO 950A R-C Bridge Part 9: Wrapup and final thoughts.
Monday, June 29, 2026 at 08:32:34
The EICO 950A has been completed. While this wasn’t really a complex build, it was challenging in that the previous owner made a mess of it before I got it.
This unit benefitted from remove the component/replace the component methodology that I used, where possible. It wasn’t possible in the power supply, which was a horror show, but everything else was easily replaced as it was taken out, as not to have too many components on the bench and too much “Where did this go again?”
The capacitor kit was purchased on eBay, and that’s what I’d like to talk about the most during wrapup.
Capacitors…too little, too late?
While the kit I purchased contained good quality parts, there were a few issues:
1: The mica capacitor in the measurement circuit.
Mica capacitors are generally thought to be bulletproof - but they are not. They are subject to the same issues as the Automatic Electric IF cans - that is, silver mica disease. You’ll be told this isn’t the case and that a mica is good forever, but searching online will reveal more than one person mentioning how they saw these starting to fail in the 90s, just 40 years after their common use.
We’re now 35 years past that, and these things are suspect. They haven’t failed - but they are suspect. First problem, is it mica? Paper parts were made on a similar body type. Second problem, these have miniscule surface cracks in the coating that have developed over the years. It’s not a matter if, it’s when they will fail. Will that be in my lifetime? I have no idea, but a new part is cheap, and there’s no excuse not to replace it.
In particular, I had a hard time getting a stable reading on the one in my unit - possibly because of moisture ingress over the years. The surface of the part didn’t look that great either, to be honest.
2: The main 8μF filter.
There’s nothing at all wrong with the part in the kit, but B+ in this unit is 600VDC - and that’s at a reduced line voltage. If your line is running 125 like most do today, your’re going to exceed the value of this capacitor by a wide range instead of the 7VDC I was exceeding it by. While the capacitor is probably going to hold up to this without too much issue, a weakened or older part could pop. As higher voltage parts aren’t really easily available these days, the best solution (even if it’s not a good one) is to take two 350VDC parts of roughly double the capacitance, put them in series, and use that. I’m planning on doing that at some point, but not right this minute - stay tuned for the addendum to this project.
Other than that, it was just a matter of removing the previous owner’s mess and re-doing it. It turned out well, and seems to work without issue. I had thought about replacing the tubes, but they were in better shape than I thought.
The challenge with this one was simply in the figuring it out, not in the doing. I now have a good working example of this device in my collection, even if the physical condition of the device isn’t the best.
Battle scars on test equipment are fine by me.
There’s another EICO 150, a Zenth Consoltone, and an EICO 249 waiting in the wings. Stay tuned!
Previous part of this series: https://wereboar.com … rk-and-does-it-work/
The entire EICO 950A Rebuild series
Part 1: What did they do to you? https://wereboar.com … -did-they-do-to-you/
Part 2: Parts! https://wereboar.com … bridge-part-2-parts/
Part 3: Musings. https://wereboar.com … -and-where-to-start/
Part 4a: Diving in with some capacitors. https://wereboar.com … ith-some-capacitors/
Part 4b: This thing is a mess. https://wereboar.com … hing-is-just-a-mess/
Part 4c: Cleaning up the mess. https://wereboar.com … up-the-power-supply/
Part 4d: Let’s do some more parts. https://wereboar.com … -do-some-more-parts/
Part 4e: The light isn’t a train. https://wereboar.com … think-i-see-a-light/
Part 4f: Finishing up the range switch. https://wereboar.com … up-the-range-switch/
Part 5: The power supply. https://wereboar.com … -5-the-power-supply/
Part 6: The last components. https://wereboar.com … mponents-are-placed/
Part 7:Checking the removed components: https://wereboar.com … -removed-components/
Part 8: Does it work? https://wereboar.com … rk-and-does-it-work/
Part 9: You’re reading it now!
There will be an addendum to this series to replace the filter capacitor.
References
YouTube playlist for the EICO 950A Rework: https://www.youtube. … XCviSJjIoCDM&pp=sAgC
Schematic: https://wereboar.com … %20Schematic.jpg.zip
Magic Eye Test (short): https://www.youtube. … m/shorts/hYwHlrx1nR8