When we left this project in February, the unit was working but the selenium rectifier quit before I could do much with it. I believe I had enough data to make an educated guess about what size resistor is needed to replace it. Seeing as how the SICo 76 is done, it’s time to put this one back on the bench.
The suspect part will eventually come out. I think I have enough room in there for a terminal strip for the new diode and resistor(s).
This is an EICO 950A Resistor-Capacitor Bridge. It offers the things you’d expect from such a device. It’s odd in that it slots in-between the 950 and 950B, which were traditional EICO silver-face units. Not this one:
This one features EICO’s colorful scheme, much like the 145 signal tracer I wrote about a couple of years ago. It has comparator and leakage functions in addition to the standard R-C measurements. Leakage is provided by a neon bulb under a pilot jewel in the upper right corner, an unusual bayonet bulb that someone replaced with a standard #47 pilot, probably because they didn’t realize that it wasn’t working because it only lights when you’re using it…not when you turn it on.
The cabinet has seen some use and abuse.
Rusty Bottoms is playing this show tonight:
Even the inside is rusty.
The chassis shows a similar amount of rust. This thing had a wet, hard life.
That aside…let’s look at the inside.
Jay Hooks makes a lot of appearances here.
The underside, however, is “Mah boi, what did they do to you?”
Everything has j-hooks. Everything. Parts. Wires. Everything. ~~Why???
Exactly what was the previous owner trying to resolve here? Was the thing on fire? It amazes me this thing worked at all, especially with those capcitors flying around with no insulation. With all the wires being j-hooked to other wires…it’s like the person just replaced everything for no reason than to replace it.
I’m going to take this challenge, but I need to get a schematic first. I’ll look for one…stay tuned. Hopefully we can make this device a bit happier.
This was an interesting chassis. Not because it’s anything unusual in what it does, but because it definitely shows it was the lower end of the spectrum. Heathkit, Knight, EICO - all of those showed some concern and care in how parts laid in the chassis. This one? Not so much. Things everywhere, parts flying from one side to the other, such a mish-mash of parts and styles and type. I’m still not sure if this one was factory built or kit built, seeing as how it has pop-rivets for everything mounted on the chassis. Seeing as how some of the parts interfere with others, it probably was kit-built.
What do I think about this device?
There wasn’t really anything different about this rebuild except that it required a lot more thought on how to place things, I couldn’t simply move strips around a little or remove parts without drilling them out. That was quite the pain, but it was worked through and eventually everything was re-installed.
I took the opportunity to use some new sleeving I’d purchased, since many of the parts had spacing far longer than anything you could purchase without special dispensation. These parts had a lead j-hooked on, and run to their connection points. I tried to stick with more modern parts like 1% films, good capacitors, and the like - except for the one used in the leakage circuit. This 1.8MΩ @ 2W was hard to find, so I just chose another carbon that was closer to the marked value. It’s not really like it matters, but it is what it is.
I couldn’t get the unit to do much of anything. The eye would close when a part was attached, so something was happening. I’m not sure if the instrument is just that low on the scale, or if the parts I have are bad to the point of being unable to be tested by this device. Regardless, it didn’t seem to do much, and that’s pretty much what I expected. This wasn’t about an accurate instrument, it was about the rebuild process.
That’s all. This is just a footnote shelf queen. Next up is the Simpson 715, finishing up the rectifier section. After that, an EICO VTVM finally gets it’s time on the bench, and perhaps an EICO 950A - assuming I can find schematics for it because that one is a mess. Stay tuned!
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.
It’s time to power up the unit. I brought it up with a death cheater, and B+ settled in around 130VDC.
That’s probably about right for this, so I replaced the death cheater with a normal cord:
And brought it up assembled and stuck a capacitor in it.
Yeah, it doesn’t do much. Either all of the parts I chose are unable to be tested by this device due to bad components or something else, it didn’t do anything. The eye does close upon part connection, so something is home inside. Just…who knows what it is.
But never right after you did the work. You have something called confirmation bias that that point, that means that you just put it there so it must be right and you’re not going to catch mistakes. Take some time away from the unit, maybe even the next day. You want to kind of forget what you just did.
Here’s the chassis, completed so far:
It’s still messy, but less messy than it was, and all of the parts are of known values.
Soldering
Soldering a chassis like this is always an adventure…I do each part in sections, so multiple components might get mounted before I solder things. Sometimes, I don’t solder things right away because I’m thinking that terminal may need something from a later section…regardless, sometimes things do not get soldered. There were a couple here:
Misplaced parts
There was one part I put in the wrong spot. The 180kΩ resistor that’s behind the capacitor in the foreground attaches to the lower terminal of the potentiometer in the background. That should have went to the top terminal. This was an easy fix, unsolder, trim the lead, and re-solder.
Missing parts
Here’s the jack on the back of the unit.
You can see there are two wires on the terminal. There’s also supposed to be a capacitor on that terminal to ground, and that part was laying right behind the unit in the tray I used to hold components. Here it is:
I was going to take it back to a terminal near the AC input, but eh. I took a terminal strip, made it into a 1 lug unit, hit it with 180W of iron and made that my new tie point. It’s a bit messy, but that solder isn’t going anywhere.
Checkout is complete. Everything is now where it should be going, and is soldered properly. Time to move on to the power-up.
Now that most of the top of the chassis is out of the way (yah right, I forgot some stuff and had to correct some wiring errors from the previous owner…) it’s time to do the bottom of the chassis.
There’s not much to say about this, so here are the rebuild images in no particular order save I tried to follow before with after in a particular section of the unit.
That’s pretty much everything except for the power cord. That comes at the very end, SICo just laid the cord over the chassis and through a tiny hole. There’s not enough room to actually pull the cord’s head through, so the back and power cord become one assembly. I’ll use a death cheater to bring it up after checks.
This thing had a rough life. It doesn’t really work right now save that it lights up and makes glow. Did it ever really work? Well…since I just wrote that, I think you can probably guess what I mean.
I can’t say I’ve seen a device that has corroded wire like this one does. Not all of them, just some.
It’s hard to see, but it’s speckled with green. I checked wires as I went, some needed replaced, some were replaced just because they were in bad shape otherwise.
The eye tube socket assembly.
Everything here was attached decently, but stuff just looked bad, and these wires were corroded.
Some new resistors and new wire, and it looks better. Still needs a bit of dressing, but that comes last.
The original builder put the eye tube at a weird slant. While the bracket itself can be moved on a slide, doing so puts the bolt for the bracket up against a terminal strip underneath because it was mounted opposite of how it should have been. That was corrected by just using a longer screw and some nuts as spacers. It’s not like this thing is going anywhere, so mechanical stresses aren’t a concern.
That’s all for the eye tube.
The grid cap for the 12C8.
This is the “signal tracer” portion of the unit, and it uses a WWII surplus tube, the VT-153/12C8. This tube was designed for radio service, and exposes one of it’s grids on the plate cap. That’s where audio is fed in for amplification. There are two parts, a resistor to ground that provides bias for the grid and a blocking capacitor for the audio so you don’t get DC in your device that’s under test.
That was easy enough to re-do.
Fairly standard work, there’s really nothing of note. It’s time to move on to the main body of the unit, and all of it’s “none of this matches anything you wrote down!” mess.
Recently, a forum buddy and I talked about capacitor measurement and devices to do such work. I decided, since I have a number of devices and access to a calibrated measurement device, to check a number of parts to see how well each device matches.
Why are we testing capacitance meters?
Simply put, there are many out there on the market under $100, and I have a number of them. I wanted to both know how these performed, and I told the forum I’d see which one performed the best. Thus, the testing.
Introduction and the devices themselves.
The reference device is an Agilent E4980A. This is a thousands-of-dollars instrument that tells you nearly everything you could need to know about capacitors. It’s calibrated, and has compensated kelvin clips for the measurement end. There are no pictures of this device in situ because, while the facility it’s in says I’m free to use it, they asked that no pictures be taken inside the facility. Sure thing, no prob. You can find pictures of this device online.
For this testing, I wasn’t worried about marked value vs. actual value, although that was recorded for posterity. All of the parts save one is NOS or RFE. These parts were chosen to be representative of the components you would find inside of an older device, especially the kind that typically graces my bench.
Capacitance meters were chosen based on the fact that you can get them, or their re-badged cousins easily at a show or online. Those devices are:
A generic L/C meter from an online shop. No name.
A FNIRSI LC1020E.
A B&K Precision Model 830 Autoranging Capacitance Meter.
A NIU M-Tester from Dayton 2016.
The leads in the picture were used for all devices except the m-tester, which needed the jig clips shown. These were made by me the night before testing using stock from my parts bins.
The parts that we’re testing.
Components were either things I had in storage, things I had bought for projects, or components removed from devices. All save the new one on the top left were suspect, leakage/etc. did not factor in to my testing.
They are, from left to right, top to bottom:
A Supertech wet, 100μF, new.
A GI 50μF dry, NOS.
A Mallory dry, 20μF, RFE
A Good*All wax paper 0.25μF, RFE.
A Bumblebee dry paper, 0.047μF, RFE.
A Solar postage stamp, 100pF, RFE.
A Sangamo Silver Mica dogbone, 1nF, new.
A Aerovox postage stamp, 6300pF, NOS.
A CornellDublier postage stamp, 10000pF, RFE.
A Bumblebee paper in oil, 0.022μF, blue wire lead, RFE. (Leaks oil.)
A Bumblebee paper in oil, 0.022uF, bare wire lead, RFE. (no leaks yet!)
A Sprague wet, 15μF, RFE.
A GI encapsulated paper, 0.033μF, RFE.
New = new part purchased within the last few years.
NOS = an old part, otherwise unused.
RFE = Removed From Equipment.
wet = wet electrolytic
dry = dry electrolytic
The rest should be self explanatory.
The postage stamps are presumed to be mica, but it’s hard to tell. Paper was packaged that way, so no assumptions are being made to their construction.
The testing methodology and notes.
Testing was simply connecting the unknown, adjusting the frequency (if possible,) and recording the value. Test frequencies used were:
120Hz - All electrolytics
1KHz - All others
The reason for this is these meters use a component of measurement called reactance. This is basically resistance of the part, with a phase angle. Geometry students will know that as a phasor, a complex number with an imaginary √-1 component. This complex number is a resistance value and an angle, -90° for a perfect capacitor.
You can’t measure DC resistance of a capacitor because it holds a static charge on it’s plates, and presents an open to your meter. AC, however, “goes through a capacitor like piss through a tin horn,” according to my first electronics instructor, Mr. Norman. This complex number is why you have a capacitor on motors. Not only does the capacitor help provide a kick to start the motor (the storage capacity of the device,) but the capacitance tries to drag the opposite force of the motor’s inductance back to zero where you only pay for the actual power used, not the power represented by the complex number. It’s basically black magic with some science added for flavor.
Regardless, data was recorded from all devices and compared to the reference unit. I originally thought that the venerable B&K 830 would provide the best measurement, as it was a fairly expensive instrument sold to industry, but that was not the case. I’m assuming this is because it doesn’t change the measurement frequency, but tries to use a best approximation for everything.
The FNIRSI device, however, came within 0.5% of the Agilent reference except on a very small value part, of which is probably due to capacitance of the leads…1 part in 100 is 1%, so any small deviation is going to show up. It’s far better than you’d need as a hobbyist and shows how far we’ve come in tech. The M-Tester and the B&K 830 kind of went around themselves competing for 2nd place, but the M-Tester offers other component tests and is really good enough for most stuff. It’s a fairly valuable device on my bench.
I realized after the fact that the FNIRSI device came with kelvin clips - I’ll re-run the test at a later date and publish new data.
The blue generic device came in third. It’s not terribly accurate, but it did the job. If you needed something and were working on old equipment, this device would satisfy your needs.
Conclusions.
The FNIRSI LC1020E, at about $80, is a superb value and will get you industrial bench performance at a hobby price. This is without using the compensated clips, so you get an instrument with leads you can reliably expect to provide good data, assuming you can set it up. The device does far more than this, and offers a staggering amount of data on the parts.
The M-Tester is a good, quick way to check all common parts, including common semiconductors. While not as accurate, they’re cheap, good enough, and should be in your travel bag if you do electronics of any sort.
The B&K 830 is meh. These still show up on the secondary market, but really don’t do anything that modern devices can’t. They are fairly rugged and can be powered from the line, so if you need a good-enough device with those parameters this is your man.
The generic one is nah. If you can get one for a couple bucks at a show, sure. It’s good to have a 4th opinion. Otherwise? Pass.
This is the second EICO 147A chassis that I purchased from the Early Television Museum - this one was considerably more dirty than the first, and looked to have had coffee spilled on it at some point. The initial analysis after acquisition is posted here if you’d like to read it.
The second chassis was very dirty on the outside. The front was covered with caked-on dirt, as was the case.
I was concerned that this was a smoker’s choice, but it looks like the dirt is just dirt. The space underneath the knobs was clean.
The front cleaned up well with 409, as did the case itself. I got a weird hit of old coffee while scrubbing the case itself…
It was mostly a matter of just some time and elbow grease. This one has certainly seen some use, some of the front panel sides are chewed up, and the bottom of the case has some rust where the paint was torn off.
This one is much worse inside than the other, and looks to have been assembled by an inexperienced builder. But, it still needs the same part as the first chassis…
This one is most certainly wax paper. It tested fine, but it’s still getting replaced. A new film capacitor was installed in it’s place.
This unit has a mod on back where a previous owner put a mini twist-lock plug on it. I replaced the cord on the socket end, and it’s polarized…but the plug in the unit itself is not. You can push the socket on any direction, so a label was applied to let the operator know that the socket needs to be attached in a certain direction:
Does it work? There was really no reason it should not work because it did before I started, but yes. Everything is now operational.
This one may eventually end up for sale, as I don’t need three of these devices. Who knows? (I think it’s going into work with me as a useable display piece.)
The Superior Instruments Co. Model 76 is currently on the bench for a rebuild, and the Cuyahoga Falls Hamfest is coming up soon. Stay tuned!
