- 2023
- Jun
- 10
Dayton purchase: An HP3440 NIXIE DVM
One of the things I keep an eye out for is NIXIE equipment. I have a few pieces in service, and as these devices age they are getting harder to find. People such as myself buy them for parts and spares, and godless heathens destroy them for the tubes so as to build clocks. It’s not uncommon to find an empty chassis where all the boards were discarded when the tubes were removed.
Fortunately, this wasn’t one of those. Cosmetically, it was in ok shape. Covers were all present, feet and bail were there, it looked it’s age. Wood screws holding the bottom cover on suggested someone had been in it and lost parts, so that was taken into account. The vendor said that it worked, but examination and experience said it probably didn’t. I was right.
The aforementioned screws told a story that someone had probably opened it, let it set, and someone else hastily tied it up for sale. It had several non-factory features installed, including both the clogged-with-mud input terminals, and the rust-onna-nut package for the plug-in module. This thing probably sat in a barn or garage for a while.
As Shango066 says, the first thing you do is look at the device thoroughly to note anything unusual. The inside had several things to see. The device had about the level of dirt I’d expect, although it’s not really that old for one of these units. Date codes on capacitors suggested this had been made (or repaired) at some point in the early 80s. That it didn’t have ICs for the driver cards suggests it’s not one of the last ones, but it’s getting close.
The first thing of note was the missing fuse at the top of the device. This wasn’t as much of a concern as you’d think, as it fed the recorder output instead of being a fuse for one of the power supplies.
The plugin module had some interesting things going on as well. One of the cards was not seated properly in it’s slot - this could be from vibration or other mechanical stress, so that was simply a matter of pulling it out and re-seating it properly. The card was slightly warped, so it had been like that for some time.
The most interesting thing here was the two orange dry electrolytics in the middle of the module. This most certainly isn’t factory, and as they were just hanging loose and kind of tied together. It’s pretty obvious this isn’t a factory part - if you hadn’t guessed that already.
I don’t know that you could get that style of capacitor in the 80s, so those may have been hanging around in someone’s parts bin, or may have even been rescued from an old television set before making their way into this device. If I plan on putting this module into service in one of my other devices, it will need to be repaired correctly.
Note the ultra-precision resistors present in this module. 10.114k (!)
The bottom wasn’t as bad, but still showed some work.
There was some dirt along the wires indicating it had been in use for quite some time, and one of the clamps was broken. I’m not sure if this was due to age or someone moving wires frequently, but it’s not that big of an issue. The big takeaway here is the rat’s nest in the upper left hand corner of the unit. The string ties had all been removed and this bundle had been poked at numerous times. Nothing was broken or showed signs of insulation damage, so I ignored it and moved on.
So…what’s actually wrong with this unit? As you can see from the first picture, almost all of the tubes light up. The second numeric tube has some bad segments, but that’s to be expected. This unit simply didn’t DVM. Normally, the neon lamp to the left will flash, one flash per read. This one did not, it was like it was in hold mode. You could mess with the 8000 button, and the sample rate control to get it to manually change, but it was not performing those reads automatically like it should.
Often times, that will be because the cards are in need of an edge cleaning, so I decided to do that. You simply pull the card, clean the fingers with a pencil eraser, make sure it free of debris, and re-insert. I have to do this to most of my units once a year or so.
This is the power supply card. Notice that there’s been a lot of repair to the unit, as evidenced by the flux-coated joints. This is not how HP would have left anything from the factory. There’s also a bit of corrosion on some of the larger joints, as evidenced by the darkened solder. This has been exposed to some dampness at some point in it’s life.
The fingers weren’t that bad, normally they exhibit marks where they’ve been placed and removed multiple times. This may have just been out a few times. Power supply is operational, so nothing to do here other than clean and replace.
This is one of the NIXIE driver cards. The fingers on this didn’t indicate any removal, and none of these cards showed any repairs.
How does this work? These are an up-counter with a wheatstone bridge. One of the bridge sides is a ramp voltage, another side is the unknown input. The ramp voltage increases and the cards count up, when the bridge becomes balanced the unit stops counting and displays the unknown input on the tubes. Of particular note is how HP decoded the output - the black “socket” for the tube contains a photoconductive plate with neon bulbs driven by the flip-flops on the card. Depending on what sequence of bulbs is lit, certain parts of the photoconductive plate are active and drive the segments of the display tube. It’s fascinating how they did that and is worth a paper of it’s own. Maybe for a future post?
Here’s the card that’s most likely the problem. The ramp generator. It had marks on the fingers indicating this had been in and out of it’s socket many times. It, for some reason, also had a lot of bug debris on it. Only this card hard that, so I wonder if this was pulled from another unit originally - usually when insects get into a device like this, their crap is all over the thing.
If you look closely, Q8 right in the middle of the card has been lifted as if someone was troubleshooting the device before I got it. So this is indeed the problem (probably!) and if I wanted to fix the device, I’d start here.
But, that’s the thing. I bought this knowing that it probably didn’t work due to the condition of the unit. It was purchased solely for parts, and parts it is. I’m not sure how much time I want to spend on this, but who knows. I may have a spare ramp card in my box ‘o junk, as I’ve purchased these units before in tear-down condition. I might wait until the snow flies and dig that box of cards out of storage and see what’s in there.
Until then, this unit is going to serve it’s function of being a parts donor for my other units.
Stay tuned, next week there’s one more show’s worth of pictures to post until late summer. The Butler Breezeshooter’s hamfest was a nice show, and I brought home stuff I didn’t need. As usual!
- 2023
- Jun
- 3
Dayton 2023: Stuff I drug home.
I made good on my promise to not drag home too much junk this year, but a few boat anchors did manage to make their way in my car. Both of them had an immediate use, but the one that was going to go in to the rack didn’t work. Not a big deal, but still…it gives me a chance to re-engineer some stuff. The rest of the items were parts for later use, whenever the need arises.
Just some random bits I picked up. An old LED display (made in the USA!) from Rat Shack, and a 1971 Allied/Radio Shack catalog. The catalog is fascinating, the prices that some of the things cost was incredible, and it’s interesting seeing some of the Shack’s staples like the Weather Cube. It’s fun to look through it and see things I wish I could still buy.
A vendor was selling older Jim-Pak parts, as well as a handful of things from other vendors. Some were $1 per, others were 2 or 4 per $1. I picked a selection of parts, as well as some of those oddball fuses old meters used for their current sections.
This is a unit that was meant to monitor the audio feeds in a studio. At it’s heart, it’s two “channels” with a center channel. Unfortunately, it didn’t work. Examination reveals a lot of white corrosion on the input board, and it looks like some water was spilled and lay on the board for a long period of time. That’s not really a big deal, I’m thinking a couple of LM386 ICs can fix this guy right up. I’m not interested in studio accuracy, I want something for my rack that I can connect to the plugboard for audio testing.
According to the vendor, this works. Well…it didn’t. Mostly. I picked it up for parts since many of these are being torn down for the displays so they can become clocks. :( The device itself had a hard life, evidenced by the replacement screws in the bottom and the considerable cosmetic damage to the unit itself. It had all of it’s feet and bail, so that’s quite nice.
An examination on the inside revealed many repairs, some boards that had left their slots, and a missing fuse. Bringing the device up on power revealed that it indeed did not work, the master clock was not present so the device wouldn’t sample. One of the tubes was also partially bad, but it had the incredibly rare polarity indicating tube, probably worth the price of the device itself.
While cleaning the card edges I found that the clock card had a transistor leg lifted, so someone was troubleshooting the device when it was put aside. As this was supposed to be a parts unit, I’m not sure how far I want to go fixing it - if at all - but it will be the subject of a future post detailing the examination.
This is one of Radio Shack’s oddball devices from the CB radio era. It’s a crystal-controlled device that listens to Channel 9, which was commonly used as the emergency channel It was designed for antenna passthrough, and has it’s own speaker. If I can find a schematic for this, I may see if I can re-tune it to Channel 19, since there’s still a little activity there.
A friend of mine said he wanted a 2-pin cable for a battery box project he made. Said he needed an extension, so I found this. It’s not going to get warm anytime soon.
This was a CB-era piece in the bins with the Jim-Pack parts. I don’t know why I got this other than it’s funny. Rip-off characters, anyone?
The slim haul wasn’t because I didn’t see things I wanted. I did. A lot of it. There were a couple of pieces that I saw that I wanted to bring home, but didn’t have a need for - a WWV receiver and some other devices among them. I figured if they were there Sunday, I’d bargain, but they weren’t. That’s me being told that I don’t need them, leave them where you found them.
(But you know very well if i see that receiver again I may pick it up because I’m being told it’s still here so you know you want it!)
Overall, I think I got some good stuff. The meter may make an interesting project, should I decide to repair it, but I think it’s just parts with a good plug-in for my other devices.
Next show is Butler, PA, and then nothing for a few month. Stay tuned for some show posts from that one, and some detail posts on a few of the devices I’ve picked up over the last year.
- 2023
- May
- 2
The TUSCO Amateur Radio Club 2023 Show - Junk I Took Home.
I tried to limit myself to Small Things this year, and not drag home any projects. I almost succeeded!
The meters are of particular note, one was an old, old, old unit with a telephone test jack on it. I occasionally have need to test single-line analog jacks, so I offered the guy $10 for it and he took it. The other meter, an Ohio-made Triplett, was a beast of a unit costing $200 when new in 1992. It’s loaded with functions, and has internal relays to isolate and switch inputs. Quite unusual and cool.
The other items were simply parts, unusual test equipment, or books. Not pictured are some RCA tube manuals I picked up for $5 each. You’ve seen those before.
The ZM-11/U - this is an interesting piece of equipment. It’s a fairly precise bridge for checking capacitors and inductors, and uses an eye tube as an aid to the relative quality of the device under test. It’s in pretty good shape physically, a few dents and dings and one broken bail on a clip.
Electrically, the vendor said that it worked (and it all lights up,) but that the internal 1Khz source was dead. Feed it an external precision source and it’s fine. I’m planning on digging into this device at some point, it needs a cord and some minor cleanup. I’ve already removed the line cord as it was in bad shape. When I get to it, that will be it’s own post.
Next up is Dayton on the 19th of May, but until then, enjoy the pictures!
- 2023
- May
- 2
The TUSCO Amateur Radio Club 2023 Show
This was the first time I’ve attended this show. I wasn’t sure what to expect, but it turned out to be pretty good for being such a small show. I spent about an hour and a half wandering the two halls, looking at thing and re-checking them to make sure they didn’t want to come home with me. I left several things behind but brought home several more.
This show was at the Tuscarawas County Fairgrounds, and occupied one of the commercial buildings. There was mention of a “trunkfest,” so I suspect that there may have been some outside stuff had it not been a rainy day. Overall, however, it was a good way to spend a Saturday morning. I’ll probably go next year, time permitting, since it’s so close.
- 2023
- Apr
- 28
My haul from the Cuyahoga Falls Hamfest.
As usual, there was a lot of good stuff to be seen at the show. I had to force myself to not bring it all home because a lot of it isn’t useful (to me) past a “Wow, that’s neat!”
Boxes of relays from the “Pay what you want table.” This is all donations for the club, and was the estate of a now silent key.
Hayes 56k modems that were part of a BBS. Yeah, I don’t know why except that they’re a matched pair.
An interesting Ethernet to Serial gateway. Vendor said it was from a friend who was doing some odd project. It was free, with the caveat that it’s a project case if it doesn’t work.
Jacks from Rat Shack of the past. Nothing more to say about this.
Adventureland is the game that’s credited as defining the Interactive Fiction genre. While the original release was for the TRS-80, the VIC-20 version wasn’t far behind. I don’t have a VIC, so this cartridge is more as a piece of computer history than as a useful item.
Of note here is this Regency counter. This device is kind of unusual for something Regency produced. It’s a fairly competent piece of test equipment with a crystal oven and a known ppm deviation. Apparently, it was designed for FCC compliance checks (at the time of manufacture.) It works, but needs an alignment. If I can find some service data, that will be it’s own post.
I kind of wish I’d got that phase corrector device, I found out later that it went for $5 - that’s a steal and a shame, but I have no use for it.
Next post(s) will be the TUSCO Hamfest. That one was small, but excellent. Stay tuned!
- 2023
- Apr
- 16
Cuyahoga Falls Amateur Radio Club Hamfest, 2023 show pictures
This year’s show was about the same number of vendors as last year, so it was pretty good. There seemed to be more general electronics and whatnot this year, and less test equipment and other non-consumer items. Not really a big deal, there was still plenty to look at, including some vendors that I recognized from last year. I didn’t take as many pictures because of that, and missed some opportunities to get more because a friend I hadn’t seen in 18 years showed up and we were chatting the whole time.
In all, it was a decent show and worth the trip. While I only brought home about as much as I did from the TMRA show, it was only because I had to stop myself from dragging home more - there were a number of things I’d have like to had, but just do not have the room.
Enjoy the pictures, and I’ll be posting my haul a little later.. I found an unusual piece of equipment from a manufacturer that you wouldn’t expect to make something like it is, and I’ll be breaking that out into a separate post - if I can find it’s service data, it will be a technical post as well.
- 2023
- Mar
- 12
A General Electric T-125A “All American Five” Radio, Part III
This is part 3, and the final part of working with this radio. It didn’t turn out as good as I’d hoped, some of the other capacitors are leaky - and some of those are in a couplet. The customer just wanted it to make voices come from the air, so I’ve left it at that for now.
The original diagnosis I came up with was bad filters, and that was the case. The original electrolytic capacitors were bad, and were simply acting as opens instead of capacitors. The device in questions was a dual section, wax sealed tubular device, consisting of a 50uF and a 30uF part. I chose to replace them with Cornell-Dublier 47uF capacitors, which should be good for another 50 years. The across-the-line capacitor also got replaced with a Vishay 0.047uF @ 600VDC device. Just as good as the original without the bumblebomb problems.
The parts, fresh from Mouser:
What we’re working with. The black tubular part in front, and the metal cased tube in back are the suspects. If you look in the middle of the board, you’ll see a reddish-brown rectangle That’s the couplet, and was a cost-saving multi-part unit. When they go bad you rebuild what’s in them…
Other problems reared their head as it was being taken apart. The biggest is the age of the plastics. The knob used a metal band on the plastic to tension it on the shaft of the tuning capacitor. Pulling this knob from the shaft left the tension band on the shaft (it had little ears that were probably used during manufacture as an install aid,) and the plastic is so brittle and dried out that it just crumbles to dust. There was enough left to put it back on, so I broke the ears on the band off and replaced the tension band and said “Don’t touch this again” to myself.
The other bad thing, and something I didn’t notice before, is the speaker had a tear. The paper was so rotten it felt like wet tissue and just kept tearing itself. Well, it still works, and this can be replaced easily enough if desired.
So, on to the repair. It was a simple matter to desolder the parts, the heavy copper on the board let it’s old solder go with a 35W iron and some wick. The parts pulled out easily and the board cleaned up well.
You’ll notice the board is discolored. That’s where the 50C5 power amp tube sits, and it gets toasty. The solder joints are exhibiting potential cracks, so they all got touched up.
The parts I installed were much smaller than their vintage counterparts, so they got bent leads to sit down on the board, and were just placed in the board. I wasn’t going for a beauty contest here, they need to be in there solid and electrically correct. You’ll notice the one electrolytic is offset a bit, I realized after I put one in that the banana slicer had one section larger than the other. Oops…that other part goes in the parts bin.
For the filters, I just jumped the two together with a loop, looped a piece of bare wire around the common and soldered it all together. The original capacitor was full of old wax and wasn’t being rebuilt.
It was all back together…but there was still no joy. The filters took care of the buzz, and the output was nice and strong - then it started to fade and get fuzzy as something started leaking. One of the coupling capacitors or other small filters on the plates is probably leaky and drawing things out of tolerance, or a tube is bad. On a whim, I tested a few of the tubes, and they seem ok, so it’s probably one of the capacitors. With some being in that couplet, that’s more of a job that a “I’ll take a look” can cover.
A short clip of the radio playing. When it’s first turned on, it’s nice and strong but fades quickly. Sorry about the download, Youtube has decided that I need to verify my identity once again, and I’m done with that game.
https://privateemail … 9e11/1/8/NjE/NjEvMTA
It goes back the owner this week, if they want more repairs that’s a different proposition. Some of the younger members of that family are starting to get into electronics, perhaps this is a good project 15 years down the road.
Beyond that, it’s really not cost-effective to repair something like this for someone else unless they understand it’s basically a replace everything deal.
- 2023
- Feb
- 28
A General Electric T-125A “All American Five” Radio, Part II
A short update: I decided to just order some good quality parts from Mouser instead of trying to pick through the junk at a show.
While they’d probably be cheaper at a show, the three parts I need to get this radio playing cost less than $7, and that’s just because I decided to go a bit higher in quality than absolutely necessary. I should have them in hand Friday, and it won’t take long at all to get them installed.
Stand by for part 3.
- 2023
- Feb
- 7
A General Electric T-125A “All American Five” Radio
This is a radio a co-worker rescued from a barn sale, and wanted to know if it could be made to work again. The T-125A was manufactured between 1958 and 1962 (or 1963, depending on who you believe.) It still has the civil defense markings on the dial, so this radio was probably one of GE’s last radios to have this marking.
The radio apparently spent the majority of it’s life in a woodshop, and it shows. While the case plastic is in excellent condition with no chips or cracks, it’s stained with various wood coloring products. Back and original cord are present and intact, although the cord is getting stiff. It, however, exhibits no cracking so it will get left as-is for now. The inside of the radio shows you where it was for most of it’s life, being coated with wood dust.
Since these are simple inside, there wasn’t any need to grab an isolation transformer or variac, just plug the thing in. The worst that would happen would be the across-the-line capacitor would pop, so…
It exhibits exactly what you’d expect. A loud 60Hz hum, so the filters are bad. That was completely expected. It’s a dual section filter consisting of a 50uF and a 30uF capacitor, so I’m simply going to get two 47uF @ 150V caps and replace it. The across-the-line cap is .047uF at 600, it will be replaced with something similar. The only other suspect item would be the coupling capacitor between the detector and the power amplifier, so it will probably get replaced as well. The grid capacitors could be eyed with suspicion, but I’m going to leave those alone unless they show problems. One is in a couplet, which would require rebuilding the device if it’s bad.
The owner simply wants it to play long enough to go “Hey, that’s cool.”
A quick cleaning with a paintbrush and some canned air got rid of most of the dirt:
So it’s ready to repair. I’ll pick up some parts at the next few hamfests I attend.
One interesting thing about this radio is the 50C5 power amp tube. It has different color writing, so I assume it’s a (genuine GE) replacement tube. It still has something interesting about it - the getter is black. I can’t say I’ve ever seen one like this without the tube being red-plated. I have to assume this radio was on for most of it’s life. Pretty cool.
Off to a show for parts. Check back later for results on this radio.
The GE T-125A schematic.
Courtesy of radiomuseum.org
https://privateemail … 729ec/1/8/NjQ/NjQvOQ
- 2023
- Jan
- 7
The TechTran 980 standalone 5 1/4” disk drive.
So what is this thing?
One of the devices I’ve had kicking around the shop for years are these TechTran 900 series standalone disk drives. These were the main storage medium for a large test platform at a former employer. They would provide commands to a computerized telco switching frame in the form of responses to a “Read next record” command. When the project finally ended, I asked the project engineer for the drive. Turns out there were 4 units, with manuals and service information.
So, it’s a disk drive?
These have two modes. First is a “File” mode, which works like you’d expect from a mass storage device. You create a file, write to it, then read it back. It also has a “Record” mode - instead of writing files with a directory, these store records, much like a punch card would store a piece of information that may or may not be part of something larger. You would write and read records - bits of text - in sequential order.
The unit does this via a RS-232C interface, using text commands. The device can operate in standalone or passthru mode, and has all the normal serial settings you’d expect - except everything is done via switches that control what is literally a box full of 74LS chips.
How does it work?
Because the device was expected to be continually available while in operation, the manufacturer set these so the disk spins at all times, and the device loads the head on to the media whenever an operation is requested. This has the effect of only requiring the time to drop the head and wait for the record of interest to arrive at the head before the operation is completed. Normally, a drive would spin up, perhaps drop the head on the disk after it was spinning, seek the correct record in the directory, and then move to read it. These spent the majority of their life reading sequences, while the time savings was small it added up to all the years the unit was in operation. File operations, of course, required seeking the record in a directory, but there was still a small time savings in not having to spin the drive up each time.
This made for a very noisy device, as the fan was spinning, the drive was spinning, and the head was being loaded on and off the media surface over and over (with an accompanying clunk of the head load solenoid) each time. Not something you’d want in a quiet space, but the noise of the test frames generally overrode any noise this thing made.
Really?
Kind of. I’m digging into the service manual more because it has a theory of operation. It looks like the record mode does create “files,” but not quite in the same way as file mode. More on that as I understand it.
I have to say I’m somewhat surprised that these things still come up. I figured the belts would have long turned to goo at this point, and the fact they’ve been sitting since about 2000 probably hasn’t done them any good either. They had a long life, being put into operation in the early 1980s and running up to early 2000 or so. But spin up they did, attesting to the fact they were well engineered (aka cost a lot of 1980 dollars) and designed to last for a long time.
The one in the pictures, a Model 980, is going to be the subject of an attempt to make it talk to something modern, which shouldn’t be that difficult as it speaks serial. Set your baud rate to 1200 and stand by for further posts in this series.
Deleted the manuals for now, will package them up again soon!