MeghanIsMe

I was *going* to make an electronics filter, but I realized that would cause problems for people who might not know me but are interested in what I'm doing. Since I hardly post anything behind security anyway, I'd like to think that if I say anything interesting, people might want to read it or send links to it. Readers (all of you) don't mind scrolling past that stuff, do they?

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I ordered caps for my VTVM, but four days later the order was on hold at Mouser. I emailed to find out why and they said I should call customer accounts. The next day, I called that number and they said that the order had already been released and was being shipped. *shrugs*

I saved a mag-card reader/writer from the dumpster at work. A big, heavy one from the '80s. All through-hole with large socketed chips. There's a vacuum fluorescent display, some big capacitors, and an 18 volt, likely linear, DC power supply. A motor too, which I have no use for but is kind of cool. I like the idea of hacking the VFD into a clock or something.

Speaking of clocks made from obsolete display technology...there was a pretty good deal. I just bought a couple of boards with IN-12B nixie tubes on them from an Ebay seller in Moldova. I'm not going to get them until February, but I have a lot to learn before I can use them anyway. Future construction of a nixie clock will be strong motivation to keep learning. People sell sets of nixie tubes for clocks for upwards of $100, and I paid about $30 for ten of them with shipping.

Have you seen what lit-up nixie tubes look like? They're power-hungry, delicate, and have a shorter working life than modern displays. They're (relatively) complicated to make and complicated to power and complicated to control. But they sure are beautiful.



Mine are different from the vertical ones in this video; they're kind of rectangular and are viewed from the top.

I found a data sheet in Russian for them and a Ukranian doctor I'm friends with at work is going to translate it for me. He's awesome! I suspect there's a translation out there somewhere already, but I kind of wanted to involve him since I knew he'd think they're beautiful too.

Thinking about starting to use my VTVM, I did one more search to see if I could find any instructions or schematics. Since the last time I looked, someone on the antique radio forums posted a link to a scanned magazine with an full article and schematic of the unit! I was looking so hard for something like that! Posi helped me too, and I spent hours searching Google, asking on a few forums, contacting a couple people directly... nothing. Today, a quick search and there it is!

So I spent hours and days reverse-engineering it and making my own schematic. It'll be awesome to compare the two!

This is so awesome!!

It's on page 74 of this magazine.

https://www.americanradiohistory.com/Archive-Radio-Electronics/60s/1962/Radio-Electronics-1962-01.pdf

Toward the other end of the tech timeline, these are the active components in my vacuum tube voltmeter.

Another recent little present to myself was the probe to use with this VTVM, bought from a ham who sells home-built probes for numerous older pieces of test equipment. I'm going to use it for my electronics work.

I'm still really proud of myself for fixing it without a manual or schematic.

I'm at the circulation desk at a mostly-empty library today so I brought these with to work with. I'm building circuits and then drawing them out and making notes about how and why they work. I can figure out what readings should be at given points and check with the multi-meter.

I need more problems to solve! I'm excited about getting together with Lisa this weekend because, among other things, I'm going to pick up a receiver and turntable that I recall both having some problems. I was just looking at my photos of all my notes on the VTVM I repaired and thinking about how thoroughly engaging and fulfilling the process was.

I've actually been a bit depressed about the VTVM because I have lost two of the control knobs from the front. I took them off for disassembly and have misplaced them. I still keep hoping they'll turn up, but it's made me feel like I have let the VTVM itself down in losing some of its parts that have been around longer than I have.

But life happens, and I am going to try to accept this and buy new knobs and start using it as a tool. If not for me buying it on Ebay and fixing it, the whole thing might be in a landfill somewhere and I should be proud of that.

I've been working on one of those CD player/turntable/radio all-in-one things that I got through Freecycle at least a year ago. The function switch was flaky. When I got it apart, I found that the switch has like 16 itty-bitty solder points. Either finding a compatible switch and replacing in, or mapping the traces and soldering in a number of simpler replacement switches, seems like more work than is worthwhile for a relatively cheap piece of hardware.

I salvaged some boards and the CD laser and tossed the rest and can't help a nagging irrational feeling like I failed and have wasted material and am somehow a bad person for junking it. I silently apologized to the device for not fixing it as I rode with it down the elevator to the dumpsters.

Another thing that is important to me is puzzle solving that I can get really engaged in. The 15 or 20 hours I spent reverse-engineering my Ebayed vacuum-tube voltmeter was one of the more enjoyable things I've done, hobby-wise, for a long time. I want more puzzles to solve. I'm going to pick up some audio equipment from Lisa that needs work, but more immediately I have a Sigma 400mm prime lens with an aperture lever that doesn't work right. Tonight, I'm going to take it apart a bit and see if I can work out what the problem is.

I feel so *good* about myself when I fix things, whether it was something complicated like reverse-engineering a schematic and replacing a bad vacuum tube or simply resoldering a couple of wires to make a thrifted digital scale work.

Picture post!

Images of Piper the Yorkie and vintage electronics behind ( the cut )

I have updates that aren't related to electronics. I really do! Pretty significant ones even! But I haven't had a chance to think about them and write them up.

In the meantime, with apologies for those uninterested, more electronics!

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I keep ending up with weird hardware. When I had a Suzuki Swift, it was the sedan version, which was far rarer than the hatchback. Super-mechanic Juan continually got the wrong parts when ordering things for it even though the part numbers matched.

My VTVM is an oddball too. A different tube than any I can find anywhere else, and a probe connector that's been described by some folks as "the worst connector ever designed."

Most recently in the annals of Stormdog's strange electronics, on Saturday I bought a regulated DC power supply; a Kepco ABC 200M. It looked like a quality solid-state unit; for $35 it seemed like a bargain. 0-200 VDC with integral ammeter and short-circuit current protection. Positive and negative terminals as well as neutral. It's even programmable remotely via resistance or voltage level. Really nice vernier knob to control the voltage. The indicator on the front slid smoothly along up to 200 volts and back. I bought it.

At home, I put a multimeter on the terminals and found no voltage. When I turn the voltage up or down, a little bit of voltage, maybe half a volt, appears on the meter while the setting is changing, then back to 0. The meter, meanwhile, stays steady at whatever voltage I set it to.. I thought maybe there was an issue with it needing to have a load on it, or it was detecting a short circuit erroneously. The short circuit level detection pot was loose, so I opened up the case to tighten it down.

That was easy enough to do. Before I did though, I was startled to find a vacuum tube inside the beast. Googling further, I learned that this is from a line of hybrid power supplies that are partially transistorized, but incorporate a big pentode tube as well. It also has an extra switch on the front that none of the images of similar power supplies I've found has, and if there was a label for it, it is lost to time.

Of course, I cannot locate any schematics or documentation for this device that might explain it's behavior. I'm going to try emailing the company.

On the other hand, after buying the appropriate screwdrivers while out with Posi, I popped open my other vintage multimeter. It's a nifty old thing with a heavy Bakelite case and a really nifty range indicator on a big cylinder inside it that rotates when changing settings.

This one is non-amplified, and therefore much simpler. The glass protecting the needle indicator had popped out of its window, but all else seemed well. I cleaned the glass and frame off with nail polish remover on the glass and rubbing alcohol on the frame. (I didn't want to potentially damage the Bakelite with something more powerful.) I also very, very carefully straightened the slight bed in the indicator needle and cleaned off the anti-parallax mirror as best I could. It's not perfect, but it all looks far better.

With the glass fixed, and not hanging around loose inside the meter, I plugged the probes in and measured voltage from a D cell. Other than slight stickiness of the movement, which I think I fixed with some compressed air around the coil, it works beautifully. I need to buy new probes to replace the sixty-year old ones with flaky wires that came with it, but after that it may become my go-to volt-ohmmeter.

It's one of these: https://www.youtube.com/watch?v=vjMTq1AxQYo

Made in Chicago! I love having truly local, vintage gear that works! It'll be so neat to use on my made-in-Chicago Sherwood receiver.

Going back to the VTVM, I am continuing slow progress I think. I keep iterating back and forth between poking at it's innards and reading (and re-reading, and re-rereading theory), and the process is moving along. Last night, I connected a voltmeter in place of the VTVM's meter in the thought that I'd backtrace where the too-high voltage was coming from. I didn't get too far along that path before referencing and then getting absorbed in theory again, but it made more sense than last time. I'm going to try to make a simplified, functional map of the rectified DC circuit and ignore the probe circuit for now because, with no device under test, the circuit should balance out for 0 volts at the meter. Since it's not, something is wrong in there, and I think it might be one of the potentiometers.

Of course, all the fancy terminology hides the fact that I really have no clue what I'm doing most of the time. I've managed to avoid major injury or magic smoke, so so far so good.

I have a full schematic, which may even be mostly accurate, for my VTVM. That's a satisfying accomplishment after all the hours I've put in. It varies from the typical model that I can find schematics for and I don't know electronics well enough to figure out why exactly. Maybe next weekend when I get together with Posi we can figure it out. I'll see if I can get a decent scan of it for people here to see too.

I replaced a couple of wires; one was broken and one had melted insulation from when I was soldering the transformer secondaries. Oops. In know that one of the adjustment pots is bad after doing resistance measures, but I was going to put the tubes back in, plug it in, and turn it on and see if it was generally functioning well after fixing that broken ground line.

Then I realized I haven't replaced the fuse yet, so that will have to wait! I desoldered the fuse and figured out it's 1/8 amp 250 volt, so I'm ordering a pack of those tonight.

Until those show up, I'll probably get back to building that ESR meter that Posi was helping me with. I also bought a nice electronic desktop postage scale that measures up to 60 pounds today! Two bucks, but it doesn't turn on. I bet I can fix that!