- 2024
- Oct
- 10
An audio analyzer project idea from years ago.
A long time ago, I had an idea to make a 10 band audio spectrum analyzer out of meters. I’d use a pre-existing circuit from another device for the band filters, and then rectify it using precision rectifiers. Some other glue circuitry was needed, but I don’t remember everything that was planned for the device.
I couldn’t find enough of the same kind of small meter I wanted to use, so the project got shelved. Eventually, I got rid of the big audio system and no longer had a need for it - but it’s kind of a neat idea and I would still like to complete it. Seeing as how eye tubes are available from overseas sources at a decent price, it may be interesting to revisit this with those instead of meters.
There were four board completed for the project before I didn’t have need for it anymore:
This is the board for the lower 6 bands of a 10 band unit. They’re simple wide-band bandpass filters with a center loosely around the frequency of input. The more eagle-eyed among you may recognize this circuit from that Radio Shack graphic EQ with the multicolor LED display that they sold in the early 90s. It’s right out of the service manual for that device.
This is the board for the upper 4 bands. Same as the lower 6.
This is the lower 6 band precision rectifier. They’re all full-wave bridge rectifiers with an op amp to provide gain for the circuit so that it combats the drop of the diodes. Ge diodes were chosen because of their cheapness (at the time!) and their relatively low voltage drop and fast recovery. This was to provide DC for the meters themselves, which would be directly driven by the output of the op-amps.
1N34 aren’t really cheap these days, but you can still get big packs of them from auction sites relatively cheaply if desired.
I really don’t remember what this board was supposed to do except combine the two inputs at an equal rate. It was going to be doing some other stuff as well, as evidenced by the remaining circuitry - but I can’t remember what that was supposed to be. I’d probably just set this aside and spin up a new precision rectifier and input board if I were to re-start this project.
That’s as far as I got before shelving the unit. I think I’ll revisit this over the winter.
- 2024
- Oct
- 8
An Eico 145 Signal Tracer - Part 6c - I was only going to run a few wires.
I sat down tonight with the intention of tacking in the B+ lines for the transformer and running the filaments. I ended up building half the unit.
I probably didn’t need to use a big terminal strip on the left, but that’s what I had so that’s what I used. I kind of wish I’d picked up more of these years ago from Mendelson’s…
Most of the audio amp is built, I have about 6 parts left to place, the filaments (!), one AC line, and then plumb the audio through the output switch. There’s a couple of layouts that I’m not happy with, but they’re all snug and not going anywhere.
Depending on time, I’ll probably finish this in the next two parts. Stay tuned!
Next part of this series: https://wereboar.com … art-6d-almost-there/
Previous part of this series: https://wereboar.com … ng-the-power-supply/
- 2024
- Oct
- 6
That weird lightbulb in Heathkit - and other - test equipment.
If you’ve ever opened an audio generator from the tube era, chances are you’ve seen one of these in the circuit.
That’s a GE type 11098 - 3S6/5 - a 3W, 115V lamp. It’s used as a balance element for the oscillator in those devices. It acts like a PTC resistor.
The generator I picked up recently at the Piketon Hamfest has a slightly unbalanced output, with the bottom of the signal being flattened. While I assume there are probably some capacitors in there that are bad, it was suggested that I try this lamp. (Maybe…I did find a post where one of these simply needed new tubes and a tune-up.)
They seem to be widely available, as they’re some sort of emergency lighting bulb. I’m planning on ordering some and will give it a try - stay tuned for results!
- 2024
- Oct
- 4
The Aerovox Model 97 Inductor-Capacitor Checker
One of the things I picked up at the Cleveland Hamfest was the Aerovox Model 97 from this picture:
It was cheap, it was from a Silent Key estate that a friend was cleaning up, and it had a functioning eye tube - the primary reason I picked this one up. Those aren’t exactly the easiest thing to come by these days, so having a few laying around is probably a good idea.
This is kind of an oddball unit as far as checkers go - most simply use a pair of leads you put across an unknown part. This one is a bit different in that it has an inductively coupled loop that acts as the probe for the device. You place a coil with probe ends across your part and that couples back to the checker - no direct connections are made, so you save the device if the part is charged.
Unfortunately, the probe coil was not present with the device - it may have been buried somewhere in the box it was stored in, but who knows…I don’t have it, and seeing as how this is a very low capacity device, it doesn’t bother me. Any one of the Eico or Heath devices is a bit more useful in this regard.
It did include a manual, which I will enter into the wereboar archives. You can download a copy here (this link is hosted on my webhost provider’s service):
https://privateemail … 651f/1/8/NDY/NDYvMjE
I’ll be doing an internal photo shoot of this device before it goes into parts storage, so stay tuned!
- 2024
- Sep
- 29
An Eico 145 Signal Tracer - Part 6b - Continuing the power supply.
I had to make some executive decisions in where to place things here, since I have more going on under the chassis. Instead of using a leaded device for the power supply dropping resistor, I chose to use a non-inductive aluminum cased resistor. Is a 25W resistor overkill here? Yes it is. Do I care? Not at all. I also moved the filter capacitors on top of the chassis since the old device with it’s mount clip is now gone. Two holes were drilled to mount the resistor - theoretically this should sink into the chassis as well, but the resistor is more than capable of dissipating the 2W the original was designed for without any heatsink at all. One side has the connection from the rectifier and a filter capacitor, the other is connected to the output transformer, and will run to various points in the circuit itself.
The only thing left to connect to the filters is that second connection, then it can be soldered.
Will this cause some hum? Maybe, but the audio output transformer lead was already as long as it is now, so who knows.
You can see the filters, laying against the chassis, going to a ground point near the output transformer.
I also connected the grounds at the input, and soldered one side of the 50pF capacitor down.
(I don’t know why I ran that wire from ground like that. I’m a stupid wereboar and got rid of it later.)
Last, is the ground point on the audio output transformer side. The transformer itself is a little smaller than the holes drilled, so was this a replacement? No idea, but I went ahead and drilled a new hole for it so it’s not flopping around on the chassis. The original transformer mount hole had a small ground tab in it, I went ahead and recycled one of the terminal strips from the bottom as a ground. This point has both filters, the speaker, and the output transformer connected to it. Since this is a fairly important ground, I hit the chassis with some scotchbrite and soldered the tab in place, insuring a nice, solid connection.
There’s a bit of solder splatter there to clean up.
You’ll notice that the output lead for the transformer is coiled up. I’ve been trying to avoid trimming any length from parts left on the chassis, just in case.
Just to note, I am in no way concerned with making this look original. It’s going to be a working device, and that’s it. I’ve tried to select good parts, so barring tube failure this thing should work for many years - and I may just get a set of tubes regardless to populate the device when it’s ready for service.
Stay tuned for part 6c, a few more connections and we’ll test the power supply!
Next part of this series: https://wereboar.com … -to-run-a-few-wires/
Previous part of this series: https://wereboar.com … tarting-the-rebuild/
- 2024
- Sep
- 27
An interesting modular digital trainer.
No, this doesn’t help you keep your digimon in check. At least, I don’t think it does…
I picked this interesting digital trainer device up at the recent Cleveland hamfest. Why? I’ve been getting back into experimenting now that I have a bit more time, and I don’t really have something like it. Sure, I have breadboards and things, but this has some amenities like indicators, switches, and a couple of clocks onboard, as well as power supplies. It’s made by a company called Dynalogic, and they specialize in modular breadboard systems for schools - this one even has “University of Toledo” (Ohio) on the bottom.
(Dynalogic has a website, but the last date is 2010. Not sure if they’re still in business or if they just don’t update often.)
It looks like a piece of late 1970s kit with the black case.
The power supplies, while operational, are a little low. 5V was 4.82, and both 15s were 14.4. Probably some bad caps in there, which wouldn’t be surprising for the age. I’ll open it up this winter and give it a check.
Dynalogic’s breadboards are made to be modular, and this one is no different. The black material under the board isn’t static foam, it’s velcro. You buy the base, then put whatever board you want on it - including stuff you make yourself. It’s really an interesting way of doing it, because there’s no special things needed - just put a couple spots of hook on the back and drop it on the box.
This unit appears to require the +5 and +15 volts, which is input at the little jacks on the top left- you’re supposed to run a standard breadboard wire down to them. This gives you a metal contact to tap from and run the rest of the devices on the board. As stated before, it features 8 indicators, 8 switches, 3 clocks, and some prototyping space (the chips on the breadboard were there when purchased and have no relation to the board.) Pretty simple in all, this is enough to do basic circuitry and give you some I/O. Nothing on here except some 555s.
The back of the board indicates that it’s hand soldered. Whether this was from Dynalogic or by a student, I don’t know. But in wasn’t wave soldered, that’s all I can tell you. You can see the velcro hooks.
Overall? This is a nice piece for the few bucks I gave for it, and it was drawing a lot of interest when I took it with me. I think, after cleaning up the supplies, that it will find a nice home on the bench.
- 2024
- Sep
- 21
An Eico 145 Signal Tracer - Part 6a - Starting the rebuild
This post starts the rebuilding of the Eico 145 signal tracer I’ve been working with since picking it up at the Breezeshooter’s Hamfest in 2023. This will consist of probably 4-6 parts (maybe more,) depending on how much time I have to work on it.
The first part is starting the power supply - I’m not going to do this exactly as the manual says, since there will be some extra stuff on the chassis. I’m going to do the power supply completely, then generally follow the assembly manual for the rest of the device.
First things first, I noticed the 4 position terminal strip closest to the rectifier tube couldn’t be mounted like the assembly drawing shows - it’s too long! That’s why the original builder chose to turn it to the side. No matter, I needed more positions so I put a longer strip in and turned it perpendicular to what the manual said. This gave me some room to add the two heater cutback diodes at the top of the strip. I didn’t bend those leads in, but chose just to drop them in the strip and solder. No, that’s not the way you’re supposed to do it, but I made sure the solder joint was solid.
I’m trying to keep the AC all in one spot, except for the filaments which obviously have to run across the chassis.
One thing you should note here is that one side of the filaments, and the center tap of the primary all go directly to chassis. This may seem kind of odd, but it helps reduce the hum present in the unit. Instead of connecting grounds everywhere, I tried to keep all of the AC running to the same ground tab. We’ll see if that makes any difference.
It is kind of a mess here, but I didn’t want to cut wire off the transformers, so I looped it where needed, and used the length to try and neatly run things to their destination. It is what it is.
Everything except for the filaments, and the AC return from the switch has been wired in. I’ll do the rest once I get the proper color of wire (more on that later.)
The only other part I did tonight was replace the front panel pin jacks on the input with a nice set of banana jacks. These are much more useful to me than the pin jacks. Note the new 50pF mica laying on the terminals, this was being sized but I don’t want to solder it in until I get some more wire.
Next part will involve placing the new filters and the rest of the power supply components.
Next part of this series: https://wereboar.com … ng-the-power-supply/
Previous part of this series: https://wereboar.com … cer-component-notes/
- 2024
- Sep
- 20
An Eico 145 Signal Tracer - Component Notes
It doesn’t really mean anything, but I wanted to check all of the components I took out of the Eico 145 Signal Tracer that’s currently on my bench. There was nothing unexpected here, most of the parts had drifted out of tolerance - or in one case, broke upon removal.
I didn’t test anything for leakage, and that’s probably where the majority of the issues would be.
The resistors were all carbon comp 20%, and most of the capacitors paper wax - assumed 20%. One ceramic tube capacitor was present - supposed to be a mica - as were the electrolytic filters. The electrolytics are assumed to be -20% / +100%. ESR on these wasn’t bad, but they’re due for replacement regardless.
Some capacitors weren’t present in the device, I’m not sure if they were never there or if they were removed for some reason.
Here’s the parts and their values, no particular order.
Next step is to start rebuilding. I’m going to deviate from the assembly diagram somewhat and build the power supply fully before moving on to the next part.
Next part of this series: https://wereboar.com … tarting-the-rebuild/
Previous part of this series: https://wereboar.com … ignal-tracer-part-5/
- 2024
- Sep
- 19
The McMurdo Silver “Sparx” Model 905 Signal Tracer - Photos
One of the things I like to do before closing up a device (permanently, or for a while) is to do a good photo retrospective showing layouts, parts, etc. It usually will be submitted to someplace for posterity, and displayed here for your enjoyment. You can also check out Radiomuseum, who accepted a number of pictures for their exhibit on the device.
The 905 tracer is going on display for the moment, so here are some photos of all the goodies inside:
The front of the unit. The pilot lamp was not original on this unit, and this one received a nice LED bulb. I pulled the screen out and knocked the dents out as best I could, you can still see a little wrinkling there.
Here’s the back. Note the big holes for cables at the bottom, this one only has a power cord.
You can reach in and touch the transformer taps. Designed for those who have some sense.
This unit has little dimples for the feet, so no crushed rubber.
The side. It’s…the side.
The device uses a leather handle. It’s still intact, but I’ve tried not to use it.
Here’s some shots of the chassis:
The best part - the tubes are all lit up:
In all, this is a pretty cool device and doesn’t have a lot of things other than it’s basic function of amplifying sound. For now, it’s going to be a showpiece - but eventually it will be used as a small amp in my main room, as I already have a tracer I’m working on rebuilding. I am planning on replacing filters and other electrolytics on this at some point, so stay tuned!
- 2024
- Sep
- 15
An Eico 145 Signal Tracer - Part 5
Before you can put new parts in, you have to take the old parts out. So I did. I decided to just pull everything, clean up the connections, and replace everything all at once. Would I suggest doing it this way? No, not unless you’ve got a decent amount of experience building this kind of device, you have a decent amount of experience in general, or you’ve done this before. It’s better to replace each part individually - but since this chassis was kind of sloppy I decided to do it all at once.
To be honest, this wasn’t put together the best. Some of the components were installed properly, leads through the connection holes and wrapped to make a mechanical connection first. Others were just tacked on and pulled right off with the application of a little heat. Others were simply run willy-nilly with electrical tape and whatever was available. I have to assume that it had been repaired a number of times in it’s past. Hopefully, now that the chassis is clean it will look a little better going back together.
There were a few things left in. Transformers were left connected in some spots, and the jumpers that run around some of the sockets were left in place. All other things were removed.
There are surprisingly few parts in this thing.
I’m planning on measuring some of them later to see how far they’ve drifted, but I did decide to check the electrolytic to see if it was bad or good.
Yeah, they’re ok. Well within the -20/+100% tolerance, but the ESR is creeping up. They’d probably be fine for a while longer but there’s no need to keep them in there.
Something of note here: If you look at the removed parts, right beside the dual-section electrolytic is a little white tube. This is C1, which is supposed to go across the input terminals. Parts list says it’s a mica capacitor, and the drawings seem to show a mini postage stamp. That’s a ceramic tube capacitor - was that original, or did it get replaced at some point in it’s life? It’s old enough that it could be original, but who knows.
Next thing to do it start rebuilding. I may wait a while before I get to that, depends - if this is a rainy fall, a suitably wet Saturday may see this thing put back together. I may also just build each stage on it’s own once I get some suitable wire, and we’ll start with the power supply.
Until then - stay tuned!
Next part of this series: https://wereboar.com … cer-component-notes/
Previous part of this series: https://wereboar.com … ignal-tracer-part-4/