An EICO 950A R-C Bridge Part 8: The rework; and, does it work?
Monday, June 29, 2026 at 07:47:09
Yes. It does.
Let’s take a look at the completed unit:
Some closeups of the the rework:
I did some basic power supply checks to see how things were performing:
That’s the voltage across a 600VDC capacitor. Line voltage here has been reduced to 115VAC to be more in line with what this thing was expecting when new. That’s not good, and this is even with a well-used tube. It rode as high as 607VDC, and if your line is 125, you’re going to see perhaps 612VDC or more.
There’s a chance that, if left on for a long period of time - especially with higher incoming line - that this capacitor could pop. I’m going to have to fix that. For reference, this is the main filter in the unit.
This is the other filter capacitor in the unit, and it’s a far more reasonable 145VDC. Well within the capacitor’s ratings.
Let’s see it work!
For a test, I took a 20+20μF part removed from another device. Checking with a modern meter reveals one section of this unit to be ~24.6μF. I hooked the part to the unit, and dialed in until I reached a good eye opening.
The eye opened wide, indicating that the part was useful and not leaking everywhere.
After a bit of finagling with the dial, I was able to set it to the proper place. This is about the only calibration you can do to one of these - take a known quality part, measure it, and adjust the dial until it reads what it should. Don’t have a capacitance meter? Use a high-quality film resistor instead.
The unit is functioning as expected, so beyond fixing the filter issue, we’re done! One more post, and then on to some new things.
Next part of this series: https://wereboar.com … -and-final-thoughts/
Previous part of this series: https://wereboar.com … -removed-components/
Wrapup and final thought: https://wereboar.com … -and-final-thoughts/
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