In the last part of this series, I put some new transistors in the device. And had to replace them once again because they were inserted incorrectly.
With that being fixed, it’s now time to check the unit for actual operation, make one final mod, and see what we have. Here’s the data:
What the manual says:
What the old transistors said:
What the new transistors said:
And finally, the noise levels:
The noise is very similar to what we saw after Q3/Q4 replacement, so the previous transistors, while providing the noise, don’t seem to be causing it. Some commentors on the youtube videos suggested the resistors are probably doing it, and I tend to agree. Old carbons are noisy.
The transistors also show some improvement in voltages, especially Q1 and Q4. Q1 should be off when measured in this configuration, and it is. Q4 is now closer to the Vdd rail, as it should be. Current draw on Q4 has also reduced, but is still high - probably because it’s amplifying noise. We’ll see what resistor levels do to that.
The final piece is to change the meter level. You really have to drive this thing hard to make it deflect, and I don’t want that. Calculations made during a forthcoming video suggested something around 3.1kΩ would make the meter happy. I accomplished this by paralleling a resistor with the 10kΩ input, and that resistor turned out to be around 4.7kΩ. It was stuck into the holes in the terminal strip so a future owner can easily remove if needed.
With that, this project is finished. I’ll probably start a new one later to swap out those old carbon resistors - but for now, that’s all and the device is working well. There’s one more post for the wrapup, and please check out the YouTube playlist for this device.
This is an interesting piece of radio history. Originally seen at the Findlay Hamfest in 2024, it showed up again in 2025, at which point I made the vendor an offer and took it home. Silvertone was the house imprint of Sears & Roebuck, once the “everything by mail” store in the USA. Sears expanded into physical stores, and devices like this unit would be sat on a counter at the radio department so you could test your batteries. Sears, of course, would be happy to sell you new “Powermaster” brand (another house imprint) batteries if yours were depleted.
The case itself is in ok condition, but it appears to have had some water ingress at some point. You can’t really see it in the image, but there’s some rust near the front of the slope. Note the two fuse clips near the top, those would have held the probes.
This is nothing more than a simple load tester, and is full of resistors to divide the voltage down for the meter and provide some load testing for the battery you’ve connected to it. It’s essentially a specialized voltmeter.
Before we go any further, does it work?
Sure does, this new battery reads decent on the unit. Probably will work a little better once probes are re-attached.
Of interest here is this knob. It appears to have been made in Chicago, and may have been sourced just for this device by Sears. After some research on this, the company, Davies Molding, appears to still be in business!
I have some cable and probes for the unit. Both of those were probably purchased at Mendelson’s Surplus many years ago, for far less than you’d get them today…I do miss that place.
It took a hot minute to figure out where the leads went, but after some investigation I determined that the negative goes to a big mass of resistors, and the positive goes to a terminal that has a second piece of phenolic on the switch. That one became obvious when I examined it with a magnifying glass and noticed it seemed to be a bit shinier than the rest, indicating it had been disturbed at some point in the recent past. Makes me wonder, did this thing have probes on it until recently and someone wanted those vintage pig pokers? Don’t know…
There’s still a bit left to do, I have some grommets on order for the holes and still need to solder the probes on, but this is what it will look like - eventually…
Stay tuned, this thing is going to work again soon!
Last night, I sat down with the EICO 150 and started to do the final wrapups on the unit.
Apply a signal.
Nothing.
Excuse me, what?
I focused on the function switch, but it seemed to be working properly after some study. I was able to put a signal in after Q1, and have it work, so that really threw me. I was able to bypass the input blocking cap on Q1 and get more signal, but highly distorted. So what’s going on here?
I decided to try the transistor(s) I pulled out for Q1 and Q2, starting with Q1. Removed the new Q1 and just tacked the old one back in. Immediate signal improvement. A check on the new Q1, and it’s just a diode now.
I get a new transistor for Q1 and check it. It’s good…and there it is.
Leads. The pinout on the transistor is different than the OEM unit.
I replace Q1 and Q2 (which is also a diode now) and I have output loud enough to make your ears bleed.
Rookie mistake. That’s on me. Always check your parts, and pay attention to what your tester is telling you.
Next post is actually doing the final tests I wanted to do, and to try and change the sensitivity of the output meter a little. Stay tuned!
I’m not sure why I didn’t run that lead behind the other one, instead of in front. Who knows.
This device sat in my rack for many years, both providing power and USB services for various things. It quit back in March, the power supply giving out like switchers do. You can find that post at the bottom of this one.
I was going to simply toss the device in the recycle bin, but…high current switchers are so cheap these days, there’s no reason not to fix it. So, let’s open it back up:
I wasn’t able to get an exact replacement for the supply, so I got a MeanWell equivalent unit. It won’t exactly fit inside, so we’ll make do.
For this task, I drilled a hole in the rear of the chassis and connected the new supply lines directly to the input of the hub using some good 16GA wire. I probably could have used a single strand here, as the internal wiring was somewhat lacking in size - but I used two, because just in case. They’re soldered together, and covered with two layers of shrink tubing.
The other ends were stripped, terminated with an aglet, and screwed into the supply, which now sits on top of the hub chassis. Open frame devices like this aren’t something that I’d put in a place where others could touch, but for me - it’s fine. The hub is back online and working.
There’s a youtube video for this device: Coming soon.
I’m happy that a piece of what could be e-waste is now back in service.
The EICO 150 was back on the bench tonight for some transistors. I started by adding a new terminal for Q4’s output, meter tie point, and transformer input.
I replaced Q4 with a NOS NTE152, new grease, and a new mica insulator of the proper size. Yeah, I got some shiners on the wire there, I tried to be careful but even my orange stick went through the insulation. I’ll get some nail polish and touch those later to coat the wire.
The part I used was an EGC152, which is the same thing as an NTE number, as NTE purchased the ECG line from Philips way back when, who in turn had purchased the line from Sylvania.
Q3 also was replaced at this time, with a generic 2N3906.
I did some noise testing to see what was going on now:
Noise levels had calmed down substantially:
There was still too much noise, so I went ahead and replaced the other two transistors.
Noise levels calmed down to what I would consider just background nosie. So are modern transistors that much better, or were these simply dying? Well, I replaced Q4 with a device that’s barely 10 years older than the one in there, so it’s certainly not “modern” - I’d have to guess that the transistors were simply breaking down from years of abuse. The Internet seems to think that these are a “replace with capacitors” item for this unit, so maybe there’s some truth in there.
There’s a little more to do, I want to make some measurements for posterity, and adjust the meter drive a little - you really have to crank the gain to get meter deflection, much like an eye tube unit. I want to dial that back some so a comfortable listening level gives noticeable deflection.
Back to the transistors, here’s what I pulled out of the unit:
Q1:
Q1 was originally an EICO number, but the previous owner replaced it with an SK3124, twice. I assume that’s because they blew it out by connecting input to B+ on a tube device. I used a 2N3391A as it’s replacement.
This part would have been an EICO part as well, but it had a Motorola HEP 726 instead. This is a generic AF transistor, ala 2N3904, etc. I used a 2N3391A as it’s replacement.
Here we have our first EICO part. This is the complement to the output transistor, and as such is PNP. Almost any PNP AF transistor will work, but may have to be selected to reduce or prevent oscillations. I used a 2N3906 which seemed to work well.
Here’s the big boy. It’s some EICO number, un-cross-referenceable. It’s an NPN power transistor, almost anything with a few watts of dissipation and an hFe of 100 or so will work here. I used an NTE/ECG152 on the suggestion of the Internets. It recieved a new mica insulator and new grease as well. The old insulator was just a little round piece of mica and the previous owner delicately balanced it under the transistor.
I’m happy with the noise levels here, all I can really hear now is the hum from the power supply. There’s a few things left to do, I want to measure voltages for posterity, and adjust that meter level some. One more part, and then final thoughts. Stay tuned!
There are only a few more parts to do on the range switch, so let’s get them done. There are two capacitors, a ?? type and a mica type. This is what they looked like:
And here’s what they ended up looking like:
I also took the time to replace some of the … more interesting jumper routing on switch terminals, and clean up the terrible solder job. Last thing to take care of on this unit is the power supply area, and I need to decide how I want to lay this one out. Stay tuned!
Today’s board is the power supply of a Sabtronics 2000 DVM. Sabtronics is known for being one of the first, if not the first company to offer a hobby priced digital meter. They eventually expanded out into other instruments, into more specialized measurements like True RMS - also at an affordable price. Unfortunately, technology marches on and a company in the USA providing USA-made devices got their lunch eaten by the cheaper array of imports. The devices they offered still have a place today, and those bright “science blue” cases are just as attractive now as they were then.
Here’s the board:
What’s of particular note is, of course, the faint orange script “T” in the upper right hand corner. This board is more akin to the Textolite made at the GE Coshocton plant, but was made there all the same.
I always like finding a piece of home in a device. Especially one that I can use, like this meter. Stay tuned, the “T” will most certainly make an appearance again!
I did some troubleshooting on this device, checked tubes, voltages, transformers, there’s even a video about it that will show up soon and will be linked as soon as it posts. But I overlooked the obvious thing.
You see that switch in the middle of the device marked “Speaker On/Off” Good. You were probably screaming at the screen going “CHECK THE SWITCH!” I finally checked the switch. It was dirty and open. Some Deoxit later, and the tracer now works just fine.
That time was not wasted, however. I did confirm that the filters are good and that the coupling capacitors aren’t leaking, so I feel confident that I can use this device without worrying that it’s going to red-plate a tube - even though that 12CA5 output gets smoking hot.
What’s the takeaway here? Always check the little things because they tend to bite just as hard. That’s all for this device, it goes on the bench as an amp. Plenty more on the EICO 950A to come!
I picked this guy up at Dayton 2026, literally the only signal tracer I saw. This was one of two magic eye laden devices I saw, the other being one of Heathkit’s larger, upright-style R-C bridges. Test equipment of this nature was absent, probably due to the fact that what’s still working is either in collections or is being sold on eBay at the eBay tax rate.
I’ve wanted one of this style for some time, and this one was a couple of sawbucks. Vendor didn’t offer me any advice on it’s status, and I assumed that it did not work. I was correct, the device is silent and the output tube seems to be getting quite warm - much warmer quicker than a simple few minute test would indicate.
I did a bit of troubleshooting to determine if the supply was working, and it is - that will show up later in both a video and a post, as I want to get this device working.
Beyond that, there’s not much to say. Here’s the device photos:
The device is clean but dusty, and hopefully shouldn’t take much to make it talk again. Stay tuned!
More parts for the EICO 950A, this time concentrating on that center switch. This takes care of the resistors on that switch, but the two capacitors in there will still need replaced.
We’re about 3/5ths of the way done here. The power supply, and some other cleanup remains.
