- 2026
- Jan
- 16
The Sabtronics 2010A DVM Part 2: Parts and documentation.
The Sabtronics 2010A DVM presented earlier is fully operational, sans a bad display element. Those displays, The Fairchild FND357, are generally only available as old stock - but they are available. I found a seller with some reasonable prices online and made a purchase:
I bought a handful just in case. These will be stored with the unit while I finish up some other things.
In the meantime, I dug the original shipping box and literature out of storage. While it looks like some of the literature is just looseleaf copied from a different model, I do have the original manual for the 2010A. I’ve scanned some of the documentation, and will scan the actual manual when I have the chance. Here’s the docs - they look like information for an earlier device: https://wereboar.com … 0Information.pdf.zip. These are also included in the January 2026 archive zip, if you’ve downloaded that.
There was some other literature in the box, including invoices. Here’s all of those shots:
These must have been popular - this guy’s order was delayed somehwhat. But, for $90 ($430 on 12/2025) these were cheaper than many alternatives, and fully within hobby pricing.
I will get to the display replacement as soon as possible, stay tuned!
Next part of this series: Coming soon.
Previous part of this series: https://wereboar.com … ut-and-observations/
- 2026
- Jan
- 15
A Simpson 715 AC VTVM Part 2: Attempting to fix the no zero issue.
In the last part, we determined that this device was nothing more than a rebadged Heathkit AV-3, so documentation beyond the simple schematic was definitely available - including the tube voltages chart. That goes a long way towards an attempt to make this device work.
The Simpson 715 is a dedicated AC voltmeter in a small package. It’s not necessarily of the greatest use these days, but the package is kind of cool, so I decided to give it a go. It works, but won’t zero fully.
There are a number of capacitors in this meter, and some in the meter driver circuit itself. But for the most part, there are a number that must be replaced for continued operation, so I’m going to go ahead and get those replaced before continuing - and perhaps that will fix the zero issue.
For this part of the issue, the following capacitors (identified by a yellow box) will be replaced:
For the most part, these will be like for like parts, same value and voltage, except for the filter capacitor. This one is 150VDC, but it’s going to have to be higher voltage if I want to use this thing. Why? This little guy.
This selenium rectifier will need to be replaced as well. The problem here is that for a brief moment, the voltage on the filters is the rectified line voltage minus the voltage drop of the device. This is because until the tubes are asking for current, there’s no drop on the power supply divider resistor, and the full voltage appears on the capacitors. This isn’t a problem for a selenium device, which has a voltage drop in the 10s of volts. But, for a modern 1n4007, you’re going to have the full rectified voltage on the parts. It’s imperative to take the voltage of the filters up to a value that can withstand that.
Older parts may have also seen this higher voltage, but those old filter capacitors could withstand surges due to having thicker dielectric material and other construction quirks that we don’t use anymore. For this device, I’ve chosen 250VDC parts instead of 150VDC. I’m not going to replace the selenium rectifier until the device works, but that will be a future part of this series. For now, let’s just replace capacitors.
In order to do so, the unit has to come apart. The chassis is connected to the meter face at 6 points:
2 on the input terminals, these get unsoldered and removed for a cleaning bath.
2 on the meter itself, these unbolt and the board slides back.
1 on the switch, this is a nut that comes off.
1 on the pilot lamp, another nut that comes off.
Knobs, pilot jewels, and terminals all go in the ultrasonic bath for a much needed cleaning, and the face is left in an easy to clean state as well.
The meter itself is interesting. This being a Simpson device, they made their own meter movement and specified it be calibrated in a certain way:
We’re left with a chassis.
This is mostly just an exercise in delicacy, removing parts from old terminals. I get to use my new solder pick set here!
The big 0.033 on the switch goes first. This type of part tends to crack and leak. For some reason, I didn’t take a picture of it before coming off…
I may take that back off and put some ’sketti on it.
Next is that bumblebomb you can see behind the switch. These also crack and leak, although this one doesn’t seem to be one of the oil-filled capacitors. (By leak, I mean they absorb moisture and change value.) It’s not across the line, so no safety cap needed here.
I try to reuse the old tubing where possible, but some new was required.
Next is an electrolytic. A new part, much smaller than the old, goes in.
It never ceases to amaze me about the difference in sizes. Sure, the old ones had some advantages, but still…
The next one has to wait a while, but here is the part that will go in. Similar size comparison:
This part has a 680Ω resistor across it, and I’m going to replace both parts at the same time as the resistor is soldered directly across the capacitor’s leads. There’s also a 30Ω resistor after this pair that will get replaced, as all of these are directly on the meter legs.
I’m currently waiting on some parts to arrive and will install those when available. Stay tuned for part 3!
Previous part of this series: https://wereboar.com … simpson-715-ac-vtvm/
- 2026
- Jan
- 15
The Sabtronics 2010A DVM Part 1: Checkout and observations.
I purchased this meter at Dayton 2024 on Sunday. It was still in the box, had all documentation with it, and was in excellent condition save that the seller said it had one segment in the display out. I couldn’t pass it up for $20, considering it’s both that awesome 1970s blue and has some historical interest.
Sabtronics was a company that appeared in the 1970s. Based in Texas, they were pretty much the first company that offered a hobbyist priced digital voltmeter you could either buy as a kit or assembled. It offered 3 1/2 digits of precision, was fully calibratable by the end user, and even offered an optional True RMS module. Sabtronics offered other devices - frequency counters, signal generators, etc. - essentially your entire test lineup, all made in the USA for reasonable prices. The stuff even ran on batteries, if you so desired.
Unfortunately, the coming of the Japanese meters and equipment did them in, as they were unable to compete with prices offered for imported junk. Isn’t that a familiar story?
(I’ll post pictures of the box and the documents ASAP, I need to dig them out of their hiding spot!)
Here’s the front of the meter, and you can definitely see there’s a segment out.
This segment did work for a while, so I assume there’s something inside the LED package that’s broken.
The top is that lovely blue.
Inside is clean. There’s a spot for some extra parts. The displays are on their own board on a long ribbon, which should make replacement easy.
In the back is a battery holder. It’s broken, of course - that cheap plastic wasn’t very good no matter where it was built. It gets old and brittle. Was this why the device was retired?
These do have the option to run on 10VDC (!) which is a very odd voltage. I have a power adapter from another Sabtronics unit, which is what I’m running it on.
The back is normally covered by a cover that has a slide latch. I noticed that it didn’t set in the hole well, I assume due to age and plastic changing over the years. Attempting to put it back in made it crack, which is probably why every other Sabtronics device I’ve seen is missing the cover. I probably will reattach this piece with some extra plastic and glue, remove the battery holder, and permanently attach the cover. I don’t need to run this on batteries.
Ignore the extra parts, those are from the Simpson 715 that’s on the bench beside this guy.
So, does this thing work? Sure does, although I’m not sure if it’s correct.
One (or both) of those meters is wrong. I’m not sure who, but I’ll take the Sabtronics in to work and check it with our voltage calibrator. As for the display, I have some of the proper Fairchild displays on order from a NOS seller. Those should be here soon, stay tuned!
Next part of this series: https://wereboar.com … s-and-documentation/
- 2026
- Jan
- 15
Checking out some recent acquisitions - #3 - Radio Shack Lives!
Well, it’s a zombie, but whatever.
Here’s a couple of devices I’ve picked up at shows and other places, both branded “Micronta.” The first is a small DVM that’s in a calculator-style case with old bubble LED displays. It’s a model as soon as I remember to look at that I’ll put that model number here.
Apparently, this is a clone/rebadge/rework of the Sinclair PDM-35, which came in a white case.
The back has a very dirty on/off switch and a jack for a power adapter. I think that’s one of those old 3/32” phone plugs that companies loved to use before coaxial barrels became popular.
It requires a 9V battery. Let’s slap one in and measure some volts.
The decimal point doesn’t move - you’re required to move it in your head.
The device’s big brother doesn’t really agree with the measurement. It’s close, however. How about some ohms? Like 330 of them?
Big brother really doesn’t agree here.
Eh, I guess for a dollar hamfest buy, we’re lucky it works at all!
The next device is another Micronta unit, also in some sort of calculator case. This is a Model 351 Counter, catalog number 22-351. Made for Radio Shack, of course.
It comes with a manual, case, and antenna.
They simply used a standoff inside the case as a mounting point for the antenna, which itself is just a piece of chrome plated screw rod. Cost savings everywhere!
The battery compartment on this one is clean, but the battery connector itself needs some love. It broke shortly after this test, so I need to find some new ones. It’s been years since I needed some 9V snaps.
It uses the same 3/32” phone plug for power, has a screw standoff for the antenna, and a 1/4” phone jack for signal input. I have a phone plug on some clips I use for troubleshooting, so let’s slap a battery in and connect it to a signal generator. I give it about 5KHz, which should be well in the range of this device.
And…nothing other than two dots. I get some numbers rolling around when inserting or removing the plug, so the device is probably counting when triggered - but isn’t triggering.
Inside is a simple circuit - some glue, a big 6 decade upcounter IC, and some chips.
Yes, that is a National Semiconductor logo there…they made the display board, which the manufacturer of this device just purchased whole.
I plan on doing some checks on this thing, starting with the oscillator - but not today. This goes in the pile for later.
Stay tuned!
Next part of this series: Coming sometime.
Previous part of this series: https://wereboar.com … -ps120-oscilloscope/
- 2026
- Jan
- 15
A Waterman OCA-11A “industrial / pocket” oscilloscope - Part 3: Final.
About a year ago, I had a small Waterman “pocket” scope on the bench. It needed some tubes, and had a bad power switch. In an effort to clean up the pile ‘o stuff waiting for bench time - here it is.
First thing I wanted to do was verify that the switch was indeed open, and it was:
By the condition of the unit, it was used quite a bit. Maybe one of the conditions that cause this device to be retired was that open switch. It was easy enough to fix, just a jumper across the terminals. Before attempting to plug it in, I verified that it had a fuse in it, and it was good.
There aren’t any shorts, I can see the transformer load on the cord. Plug it in! I can see tubes lit.
But, there’s nothing on the screen. I mess with the controls for a while and let it set. Nothing. Upon powering down and opening, I notice I can’t detect any heat on the neck of the CRT. Well…it may be open or have some other fault. That’s a show stopper here, and I remove my new tubes for later use.
This guy goes into the donation pile. Perhaps someone can make use of the parts.
Previous part of this series: https://wereboar.com … oscope-part-2-tubes/
- 2026
- Jan
- 7
Checking out some recent acquisitions - #2 - Sencore PS120 Oscilloscope
While not really a “recent” acquisition, this oscilloscope was something waiting it’s turn on the bench. This came from the Fort Wayne Hamfest in 2024, and was - for the most part - taken because it was offered for a few bucks. I took it because I didn’t want to see it get tossed in the trash, and wanted to give it at least a chance.
I never really had any intention of using the device, but the rusty crusty case was interesting. Would it still work? Who knows. I also never really had intention of fixing the device, so there’s that. The device itself is a Sencore PS120 12MHz oscilloscope, and dates to about 1966.
Upon investigation, the obvious problems are, well, obvious. The case is very rusty as if this thing sat in a damp but not wet location for some years.
The face is similarly dirty, like this thing was in a barn or something.
There’s a lot of dirt inside the unit as well.
Of note here is the CRT, made by DuMont. The tubes themselves are a mix of brands, with the Sencore name still on about half of them. There’s nothing special here other than the CRT.
However, when looking into the chassis itself, there is one interesting note:
There’s a lot of Sprague Orange Drops in here, and I doubt those are original. I’m guessing someone was in here trying to solve problems. So let’s plug it in!
I originally thought about using my death cheater to power this thing, but the power input terminals have exposed holes. I soldered a power cord in and did some basic checks. The power switch works, and the resistance across the line is about 9Ω. That’s good, it’s the transformer primary. That’s not shorted, so let’s raw dog the thing. I plugged it into the isolation transformer with a 2A current limit. Hit the switch, and…
I get a dot on the screen. Great! However, nothing else. Focus and intensity work, but anything to move the trace doesn’t work. No manual movement, no sweep, no nothing. I’d guess this is why there are so many new capacitors in the thing, the previous owner was trying to fix this problem and gave up. The Internet says to replace capacitors and it will fix everything, but that doesn’t always work.
It does have a good CRT, and someone can probably use that. I remove my cord and will put this into the “Donate This Stuff” pile for later disposal.
That’s all for this one, it was either going to be a work or don’t situation, and it don’t work.
Stay tuned for more junk!
Next part of this series: https://wereboar.com … 3-radio-shack-lives/
Previous part of this series: https://wereboar.com … cent-acquisitions-1/
- 2026
- Jan
- 6
Checking out some recent acquisitions - #1
This is going to be the first post in a seldom-series of equipment checkout posts. I’m going to take the unit apart, see if there’s anything that would prevent it from being turned on, do some basic “look here” things, and then turn it on.
This first post is two late year purchases, one from the Cleveland hamfest, the other from Fort Wayne.
This first one comes from Cleveland, and is a standard two-tube capacitor analyzer with an added headphone amp so you only needed one instrument on your desk. It probably designed for a set of high-impedance headphones of the WWII surplus variety, and much of the unit is built from surplus parts.
This was made by the Superior Instruments Company of New York. It’s in decent enough shape for the age. It’s complete, and has little damage to the front panel - but is in dire need of a cleaning.
The back of the unit is rougher, but would most likely clean up nicely with a good scrub. We don’t even get a cord grommet here. The power cord itself is a nice gray-blue that matches the case, but is quite rock-hard at this point.
We don’t even get an underwriter’s knot here, the cord is just draped across the chassis with no thought as to how it affects the circuit.
The chassis is about as cheap as you can get. A partial internal contains almost all of the components and tubes. Tube complement is:
1626 RF Triode being used as a diode (!)
VT-153 (12C8) being used as a headphone amplifier
1629 Magic Eye
All of these are mil-variants, which suggests they had lots of cheap surplus tubes. The triode is of particular interest. The manufacturer tied the control grid to the plate, making a diode out of the device. This tube also has a lower heater current than actual rectifiers, so they could use a smaller transformer. A way to use up what most likely would have been very cheap tubes that were of little use otherwise (the 1626 is a very low gain RF amp,) and as a way to use a cheaper transformer. Cost-reduced all the way.
The bottom of the device contains most of the leaded components of the unit.
There’s probably some surplus here as well, especially those silvery capacitors with no other markings. Of special interest is that big motor starter capacitor to the left - it’s not even marked on the schematic. I also like the red Astron part in here, all by itself.
Speaking of the schematic:
The device I have and this schematic only agree so far as “yes, there is that type of part in that circuit.” Not much else does - it looks like Superior probably used whatever they could get their hands on that was close enough.
Note the 2.0μF motor starter capacitor isn’t on the schematic - it should be connected to the power factor control. Who knows if this was omitted, changed, or added after the fact. Considering this was as cheap as could be, I would guess that the person who drew it was trying to be cost-effective, but it was found out later that the circuit didn’t quite work as planned. Other capacitor analyzers I have with a power factor measurement have a big capacitor in that circuit, so…whatever. There it is.
I don’t see anything that would prevent this from working, so let’s plug it in and see if there’s smoke!
The eye tube lights up. It’s acceptable, and can be seen in a lit room.
There’s no other power indicator on this device. I guess you really don’t need one.
DC on the power supply is kind of bleah, especially for having almost no current draw. This may be a symptom of using the wrong tube in the wrong place, or a bad filter. I didn’t stick a new filter in here, that may happen later. This is just to see if it works.
So, let’s put a capacitor on it. I chose a 8μF “Mighty Midget” removed from a previous rebuild. It’s gone quite high, so we should see something well in excess of 8μF.
The device seems to indicate this is about 14μF and change - we’re reading the top portion of the middle scale.
Let’s get a second opinion.
The second doctor disagrees with the first. However:
Doctor #3 agrees with doctor #1.
So, this device is probably as accurate as this type of device can be. It goes back together for later potential rebuild.
Next up is another IG-72. I purchased this at Fort Wayne, mostly as a spare for the one I already have. It’s in ok shape.
The back is likewise in not terrible shape, and has some interesting markings.
Of note is the fact that this one has a grounded cord, whereas others I’ve seen do not. There’s also the stamp in the corner.
It says “MEISINGER BEECHCRAFT, INC.” and was apparently part of their repair area test equipment. That’s really cool, this one has a history.
It was certainly used, but not abused:
It has the obligatory soldering iron melted spots. It was also millerized - whatever that means.
The inside is clean, but dusty. The transformer is a bit loose.
Tube complement is:
6X4 Rectifier
6AU6
6CL6
The CL6 and AU6 form the oscillator and output amplifier pair. It’s a standard Wien bridge oscillator with a light bulb in the middle as a PTC resistor. Two of the tubes are most likey the original Mullard tubes, and one is an RCA.
The bottom looks to have been factory built.
The bulb was goop’d in, probably to keep it from vibrating out during use in a running aircraft.
Nothing sticks out as preventing operation. Let’s pull the rectifier, as these liked to arc across the cheap socket.
Nope, that’s good. Time to plug it in. Power is applied. We have tube lights.
The needle comes up, and look there - this one still has it’s little red film for the power lamp.
The DC on this one is so clean, I can’t get anything off the power supply. The output is equally clean.
The signal does distort a little at the bottom of the wave when it’s turned up to full output, but that’s a known Wein bridge issue. I can dial it back a little and probably be fine.
That’s all for this one - other than some cosmetics, this device is fully operational and seems to be in great shape.
I’ll have more in this series as I pick up more devices. Stay tuned!
Next part of this series: https://wereboar.com … -ps120-oscilloscope/
- 2026
- Jan
- 2
An EICO 902 Harmonic Distortion Analyzer Part 2: A well used unit.
In the first part of this series, we discovered that the power switch in this unit was bad. It also needs a fuse, so let’s replace that first. I have some of these old Seneca Fuses laying around - Seneca, of course, being a company that was based right here in Columbus before being acquired by a company called Russell Industries, and lost when that entity closed. These particular ones were made after the Russell purchase, but whatever. They’re fuses.
In order to do some basic testing, I’m going to just jumper the switch for now.
This time, we get glow.
Power supply ripple is well within acceptable range for 330VDC.
The regulator tube is doing it’s job.
The first thing I notice, however, is the meter is bouncing around. Just tapping switches makes it move, so they’re either very dirty, or worn. In particular, the main selector switch, that of being able to select the range, seems very touchy. I can see there’s a groove worn into the brass, and the remainder is very dark with oxidation. That’s not good…it’s got a lot of precision resistors soldered on to it, and would be almost impossible to source. Being the main switch, I can see where it would have had a lot of use.
But, since the power switch is known bad, I’m going to pull it, tear it down, and see what we can do with it. It’s an assembly made of various components marked Clarostat, so it will most likely be able to be torn down - and it is.
The problem here lies in the final piece on the right. That’s the business end of the power switch, but the actual issue lies under the phenolic wafer. There’s a piece of brass there, and it’s most likely worn from use. I can’t get it out because the switch itself is riveted together. Were this 1970, I would simply purchase that piece - but it’s not. I’ve sprayed and cleaned it the best I can, but it’s not giving me anything but some high-resistance wobble when I move it. Back together it goes. I’m just going to tie the ends of the power cable together and cover them for now. The power switch on the outlet strip will work as it’s power switch for now.
After some experimentation and cleaning, the range selector is very tired and worn. It’s quite noisy, and just touching it will make the meter slam to the right. I don’t think any amount of cleaning is going to help this, the brass is just worn away.
I’ve also noticed that some of the tube sockets are very worn, and a simple touch will make the meter go nuts. That’s not good either.
This unit certainly didn’t sit on a shelf and look pretty, and due to the number of components that are worn out, it may not be a useful project. I’m going to put it back together for now while I decide what is going to happen to it. Unfortunately, not every device can be saved.
Stay tuned!
Next part of this series: See below.
Previous part of this series: https://wereboar.com … rt-1-whats-going-on/
Because of it’s limited use to me, I’m going to pass this on to a friend who does audio work. He has the ability to use the device, and would have more desire to see it work than I do. It’s just too worn for what I can put into it.
- 2026
- Jan
- 2
Another S-38C on my bench, part 5: All done and wrap-up.
Welcome to 2026. The weather here was cold and snowy, so I decided to finish up this radio.
This unit was simply a “replace the parts that will go bad so we can use the device.” As such, there’s not a whole lot to say here. I did a quick check per the schematic to make sure everyone was in the right spot, and soldered it in.
I did replace the power cord along with the suspect parts, simply because the previous owner put a short extension cord plug on it. I used one of my stock power cords with a bit thinner insulation. It works better going through the grommet and looks more period correct.
The money shot:
Unfortunately, I can’t post video here as the host doesn’t allow streaming due to bandwidth limits, but the unit sounds good and I don’t hear any silver mica disease problems.
I now have a working S-38C again. I may put this one on display in the front room, as it’s actually usable. I’m not sure yet. The other one I did earlier may go back on the bench to see if I can get rid of it’s noise problems. Who knows, but stay tuned!
A comment on the loop on top - this was a cheap tuned loop given to me by a friend. It works wonders, and takes up far less space than a longwire. I know these are available on that site named after a river, if you have desire to purchase one.
Here’s the complete series list for this unit:
Part 1, Examination and Diagnosis: https://wereboar.com … ation-and-diagnosis/
Part 2, Parts: https://wereboar.com … -bench-part-2-parts/
Part 3, We have parts: https://wereboar.com … art-3-we-have-parts/
Part 4, Installing the parts: https://wereboar.com … nstalling-the-parts/
Part 5: You’re reading it now!
That’s all for this device. Next up is an EICO 902 I/M Analyzer with some issues.
Previous part of this series: https://wereboar.com … nstalling-the-parts/
- 2025
- Dec
- 31
An EICO 902 Harmonic Distortion Analyzer Part 1: What’s going on?
While the Hallicrafters S-38C is waiting for a check before plugging it in, I’m starting on this analyzer. This is a standard null-type analyzer of a nature similar to many others. You input a frequency, null out the fundamental, and what’s left is the distortion. It’s spat out on a meter and scope terminals.
These devices seem to go for a lot of money, so I was quite surprised to be able to pick it up at Dayton 2025 for $30. I believe the gentleman I purchased it from was the original owner, and the device appears to have been factory built.
It’s in need of a cleaning:
Inside it’s dusty but relatively clean. A little rust on the transformer.
And the bottom is nice and clean and shows almost no trace of work.
The only imperfection I can see is this little wire snip, and I’d say that was left from the original build.
The top has one modification, someone cut open a tube shield. It was suggested that perhaps this tube ran hot and was not operating properly (thus the blackened metal,) and this was an attempt to make it work. Rather crude, and I may see if I can get a new shield and see what happens. If this is indeed an issue, I’ll cut the top to be a bit more clean than this let’s just chop-job it.
So, it’s in great shape. There’s some wax paper capacitors that will need changed, but it’s good enough to try out. First thing, is it needs a new cord. The original is barely hanging on at the input to the chassis, so it gets a new polarized cord. It also needs a pilot bulb lens, but I have some other lamps that may fit here. Fuse is present and not blown, but the glass is cracked, so that’s changed out. Plug in, and…
Nothing.
Turns out the power switch is completely open.
I only had one jumper with me, and it was in use as a temporary fuse. So, I decided to call it until I could get a proper fuse in the unit, at which point I’ll jumper the switch temporarily.
It looks like I can get this component apart to see what’s wrong, so I may do that in the near future. Stay tuned!
Next part of this series: https://wereboar.com … -2-a-well-used-unit/