Help with ThaiKit Curve Tracer NOW W/ Calibrated Instrument  OpAmp - Page 1
Forum section: electronics / repair

author: watchmaker
author_rank: Unknown
timestamp: February 18, 2024, 03:20:05 pm
content: I changed the to account for the improvements. See end of the thread.I assembled this kit and made a nice enclosure, etc. I have twice blown up signal transistors. I feel like a watchmaking student who keeps testing his watch hoping for an improved result with no changes. Neophyte. But I like the puzzle to solve.I have the schematic and I also looked up the Elektor article for the waveform information.I verified the 2 ICs are ok and the same with the two transistors via substitution. Both chips give out clean crisp signals.I am leaving both jumpers open; small signal, NPN. Both relays click when jumpers are added. Checked all diodes out of ckt.So I am doing something incredibly stupid.Below are my waveforms at the collector and base inputs. Emitter is zero. I looked for the step signal from pin 9 of the 4024 chip but it is a simple square wave. No transistor being tested. I get the sawtooth at the scope horizontal output but nothing at the horizontal where the elektor article sez I should get a step (again, I have no transistor being tested/smoked).I get that the emitter feeds the last opamp before the power transistors.Can someone who has built this confirm my signals?Conditions are :No transistorNPNSmall SignalTHANKS!!!

author: Jwillis
author_rank: Super Contributor
timestamp: February 19, 2024, 12:25:48 am
content: Looks close to what I get with same settings. Sorry for the scope photo. Hantek USB doesn't work (piece of junk). Pretty sure it's the same kit as yours. Added the signal from pin 9 of the 4024.

author: Jwillis
author_rank: Super Contributor
timestamp: February 19, 2024, 12:40:18 am
content: Which small signal transistor are you testing. If I have one I'll see if I can blow it up.Now you have me wondering what's going on. Large transistors test fine but as you, small signal transistors quickly get hot and fail. I don't use many small signal transistor in special applications. Mostly power applications. So I didn't notice the problem until now.So given the evidence, your probably not doing anything wrong and there is an issue with the kit.

author: Jwillis
author_rank: Super Contributor
timestamp: February 19, 2024, 02:14:26 am
content: Little update. The tracer works on most of my transistors. It won't test Darlingtons. BC517 Darlinton burns up and TIP142 (also a Darlinton) just shows a dot in the middle of oscilloscope and gets hot. Bost tested fine on a BSIDE ESR02 Pro.

author: watchmaker
author_rank: Unknown
timestamp: February 19, 2024, 03:26:53 am
content: Thank you and I'll be damned. I spent 3 DAYS on this following all the signals and marking the board with w/ the paths.I just found this youtube. He does an excellent job of explaining the design and its limitations. He made me think I need to look at my 1 ohm resistor.

author: Jwillis
author_rank: Super Contributor
timestamp: February 19, 2024, 04:26:37 am
content: Quote from: watchmaker on February 19, 2024, 03:26:53 amOh Wow. Great video. Now I can take a second look at mine and make those improvements. Thanks!I was thinking about that resistor too and wondered if adding another rotory switch or switches to change the value the peak power. like on that other curve tracer he described.

author: watchmaker
author_rank: Unknown
timestamp: February 19, 2024, 09:23:59 pm
content: OK, I have no clue. I have scope pics of every used IC pin and the Collector and Base signals. Everything looks fine to me but the base signal, but what do I know and it eats transistors.THANKS for any help! I am not giving up, but I will put it away for a while.According to the youtube above, the signal at the base should look like this:https://youtu.be/7exRUNCQ-hI?t=827sI even removed the relays to determine the contacts and operation. These are marked on my PCB pic.Conditions are:NPNSignalNo transistor in testMine looks like:My Collector out looks like this:My PCB looks like this:Here is my marked up schematic:The signals at the pins for the 4024 and the tl074 will be listed in the next posts

author: watchmaker
author_rank: Unknown
timestamp: February 19, 2024, 09:29:44 pm
content: Here are the signals at the 4020 counter The caption is the location (A=4020 B=TL074)Pin 1 4024Pin 6Pin 9Pin 11Pin 12

author: watchmaker
author_rank: Unknown
timestamp: February 19, 2024, 09:35:48 pm
content: And the TL074 signals:Pin1Pin 2Pin 8Pin 9Pin 12

author: Jwillis
author_rank: Super Contributor
timestamp: February 19, 2024, 09:54:03 pm
content: Base and Collector look right. What Small signal transistor are you testing?I'll check the other readings you got.

author: watchmaker
author_rank: Unknown
timestamp: February 19, 2024, 10:48:39 pm
content: Thanks. Be very careful about changing the voltage divider resistor (1 ohm) to 100 ohm 1 watt. Put in a power transistor and the 100 ohm resistor burned right up. Put the 1 ohm back in and it is happy. I wonder if there is some kind of positive feedback going on under load?? (Superstitious thinking).Ok. I will check the morgue and see what has toe tags. Thanks again! I am also wondering (superstition again) if it is the diode cascade. Substituted both op amps with same results on signals. I keep looking at the bottom of the board but see nothing. And I would think I would not get clean signals.Also, tell me a transistor you have successfully (not barbecued) tested. I may have it.I KNOW it makes the most sense to build from the Elektor plans, but this is one helluva learning exercise.My wife is getting concerned!

author: Jwillis
author_rank: Super Contributor
timestamp: February 19, 2024, 11:28:33 pm
content: Most of the readings on 4020 and TL074 you got are the same as mine.The picture below is pin 2 Px10 X10Mag 5mV/Div 500ms T/Div from The V1050 because it produces better quality image than the Hantek at low levels.I can get a better image if I used a probe grounding spring instead of the lead.

author: Jwillis
author_rank: Super Contributor
timestamp: February 19, 2024, 11:34:11 pm
content: I need a ferrite beads on the transistor test leads. Any noisy oscillation from those and transistors get really hot. Which makes sense.also need a better DSO. This Hantek is really P***ing me off.

author: Jwillis
author_rank: Super Contributor
timestamp: February 20, 2024, 06:46:33 am
content: Quote from: watchmaker on February 19, 2024, 10:48:39 pmThe transistors that work: 2n2222, 2n3904, 2n3906, A1015, C1815, BC547,BC548 up to BC558, S9013, S9014Ones that won't work are BC517,BC337and I'm not sure why.Doing a little investigation it seems that transistors with an BEon voltage lower than 1V measure fine without heating up. The ones with an BEon voltage higher than 1V get hot and burn out after a while.This occurs on both large and small settings so Darlinton power transistors like the TIP142, TIP122, TIP117 also won't work.Edited The BC337 as being untestable. With correct connection it is testable.

author: watchmaker
author_rank: Unknown
timestamp: February 20, 2024, 10:27:08 am
content: OK. I will redo a 2222, this time I will solder it directly to the board.BUT, what good is a test device that only works on some specific items and destroys the rest?? Are the reports of success from one time users? I did ask the guy from that video to comment on this thread, but this may well be a dead end.I looked at Microcap last nite and it seems both ICs are there and I placed components on the board to wire together. Not sure what this will prove, but....

author: watchmaker
author_rank: Unknown
timestamp: February 20, 2024, 05:14:20 pm
content: OK. To falsify hypothesis thatmy LED lighting is causing too much noise, I pulled at the old warhorse, the BK 501a. Scrren shot of a 2N2222 is attached.No difference with all lights on and all lights off.As far as the ThaiKit, it smoked a 2222 soldered right to the board.Interestingly, the creator of that youtube deleted my comment requesting he comment on this thread.So, I am going to create MicroCap ckt. Run it with a 2222 in the socket. Measure the various currents, voltages and signals. Then I am going to modify my board by adding test points for current (cut trace, drill for header pins). I will compare the damned measurements against the sim.I did notice the kit uses a tl074CN as opposed to a tl074 listed on the schematic. I will look up the differences.If I wasn't trying to learn, I would throw the thing away. Now I am like a dog with an old bone. The BK does not destroy what it does not like, and the Analog Discovery has a computer based curve tracer. By the time you are done with a box, PSU, connectors etc, I think you are at 1/2 to 1/3 of the cost of either of those options with no headaches.

author: jdragoset
author_rank: Frequent Contributor
timestamp: February 20, 2024, 05:52:35 pm
content: It seems to be missing a collector load resistor between the BD 139 and BD 140 emitters and the collector terminal.Tektronix curve tracers had a switch so this could be set from low to high resistances.The 1 ohm in the emitter circuit is the current shunt.

author: watchmaker
author_rank: Unknown
timestamp: February 20, 2024, 08:50:42 pm
content: Thank you. You prompted me to more closely compare the Eleckto ckt and the Thai Ckt.OK. I am new to semiconductors.But first, when I look at the datasheets for the TL084CN and the TL074CN, especially the suggested apps in section 9 (and the block diagrams) these are two very different OpAmps. I barely learned the 4 basic configurations, and maybe they are interchangeable, but it does not look like a direct interchange to me.Among other things, the Elektor design very clearly specifies shielding the E,C,B and scope output lines.No wonder it is so hard to get info from the seller. He never even sent me the instructions and I populated the board based on the silkscreening although I upgraded the zeners.Secondly, the Elektor ckt does not try to deal with signal vs power transistors. The Elektor may be a candidate for the limiter resistor switching but it makes sense to start with the ckt as originally designed.I think I will order some TL084CNs and play. I have some prototype PCBs.

author: Jwillis
author_rank: Super Contributor
timestamp: February 20, 2024, 09:48:28 pm
content: I think I'm getting close to figuring out the problem.I redid the measurements on the transistors that didn't work. The BC517 Darlington won't work but the BC337 Does. I must have had the connection wrong before testing the BC337. So it seems Darlingtons are off the list of testable transistors.At first I thought it may be internal bias resistors but 2 2N2222, in Darlinton configuration, is also untestable. Trailing transistor gets excessively hot. It's going into full saturation because of the gain increase!Testing working transistors base voltage is around 500 to 700mV and around 20mV across 1 ohm resistor or 20mA to the base , depending on transistor being tested. On Darlingtons the base voltage drops to 0V and 1 ohm resistor reads 655mV. That's 655mA to the base It's drawing to much current for the tester to supply to the base. With a 1M resistor in series with base it becomes testable. This is because of the high gain of Darilintons. Some extra rework here is needed because of the noise. A lot of noise due to the long test leads I have.To much current to the base and the transistor goes into full saturation. Across a 1 Ohm resistor. the transistor exceeds it's maximum dissipation and burns out. So we need to limit the base current output on the tester for high gain transistors over 1000. The BC517 is a 30000 gain transistor.

author: Calambres
author_rank: Frequent Contributor
timestamp: February 21, 2024, 08:17:35 am
content: Quote from: watchmaker on February 20, 2024, 05:14:20 pmI don't think he's deleting your commets. For some time now YouTube is not allowing links in the comments and a bot deletes all such comments in mere seconds.

author: watchmaker
author_rank: Unknown
timestamp: February 21, 2024, 02:18:03 pm
content: Quote from: Calambres on February 21, 2024, 08:17:35 amThanks! My cynicism is showing.I will leave a comment directing to this thread using verbal directions (and delete my comment!.)

author: watchmaker
author_rank: Unknown
timestamp: February 21, 2024, 02:25:35 pm
content: Attached is a marked schematic of the original ckt as described in Elektor. There are some pretty interesting changes in the ThaiKit.Two schottky diodes are changed to 4148s. Now I have to learn about schottkys. Another is that load resistor value.Finally, he does not switch in IC1 pin 9 unless he wants to increase the traces. His diode tree/waterfall for the step function is also smaller.It will not be hard to revise the ThaiKit to the Elektor design while keeping everything on NPN so that I can see the difference in barbecue menus.I am still befuddled that this ckt appears to work for some people. Included components???

author: Alex Nikitin
author_rank: Super Contributor
timestamp: February 21, 2024, 05:36:04 pm
content: For starters you can increase the value of the current sensing resistor from 1 Ohm to 10 Ohm, that might considerably reduce the amount of unintended smoke (it will also change the vertical current scale to 100mA/V). The Schottky diodes would further lower the current limit and make things safer as well. As is, the current limit is close to 1A which would certainly fry any small device and might easily take out the output devices in the amplifier/integrator. A good idea would be at least a resettable fuse in series with the amplifier output, better still a proper current limit. For small devices you really want to limit collector current by about 50mA for a continuous loop. With modern digital scopes you might also investigate a "single shot" option, running only one curve tracing cycle and then stopping, keeping the dissipated energy at bay.CheersAlex

author: jdragoset
author_rank: Frequent Contributor
timestamp: February 21, 2024, 09:20:49 pm
content: If R17 (10 ohm) is as shown in the diagram, it is only acting with C6 as an RC network rather than a load.A load resistor would be between the emitter connection of BD 139/BD 140 and the "C" terminal of the DUT.

author: Jwillis
author_rank: Super Contributor
timestamp: February 21, 2024, 11:38:24 pm
content: The tl071 and the tl081 are nearly identical. The most significant difference is TL071 has a lower noise.You need to measure the current of the transistor under test. If the measurement across the 1 Ω resistor is to high the transistor will burn. Most transistors I tested measure 18mV to 23mV across that 1 Ω resistor. The ones that get hot and burn up over an extended time are Darlingtons only because of the Gain. The 1Ω resistor has 400mV to 700mV depending on transistor being tested. By adding a voltage divider to reduce the Base voltage and current, I can see the curve trace of Darlingtons. I tested the BC517 this way and it doesn't get hot. With a 910K resistor between base output and transistor base and a 300K resistor from transistor Base to Emitter. This is because I'm essentially changing what the 100K and 7K5 current limiters do. This reduces the the base voltage and current there by reducing the current across the collector emitter junction.You need to check the current across transistor under test by the voltage drop at the 1Ω resistor. That should be around 20mV which is 20mA across transistor under test.Check the Base voltage of tracer with no load. That should be around 5V in NPN setting and -5V in PNP setting.The Collector voltage of tracer with no load should be around 5V in NPN setting and -5V in PNP setting.When a transistor is out under test, the base voltage should drop to about .7VRe-check the current limiters. The 7K5 and 100K resistors. If those are not correct then to much current goes to the base of transistor under test. There should be only a few micro amps going to the base of the transistor under test when setting is at Small NPN.On a 2n2222 when tested with the small NPN setting it does not get hot.Theirs only 23mV at the 1Ω resistor or 23mA across the 2n2222 CE junction. Base voltage should be around .63V. Emiiter voltage should be 23mV and Collector voltage is 4.4V. That works out to around 100mW that the transistor needs to dissipate.If 2n2222 is tested with the Large NPN setting it gets really hot and fails after a minute or so.If your transistors are blowing up theirs to much current going to the base.

author: watchmaker
author_rank: Unknown
timestamp: February 26, 2024, 08:54:58 pm
content: Sucess!!! I wish I knew what I did, I was so fatigued last night.Anyway, the SN2222 problem was cured with a 1k ohm limiter to replace the 100 ohm.As you can see, capacitance is not really an issue. Cables do not need to be shielded.Also, it wants 1x probes!!! I was using nonswitched 10x. I do not think I will bother with 50 ohm cables. Just use the adapter on the 1x probes.Changed things so many times! Looking at the Elektor ckt did help. I will now proceed to make the mods in the video.Definitely better trace on the CRT.I will list traces and voltages soon. Right now I need a damned break and need to go back to my schooling.

author: Jwillis
author_rank: Super Contributor
timestamp: February 26, 2024, 09:29:52 pm
content: Quote from: watchmaker on February 26, 2024, 08:54:58 pmAwesome! Which resistor on the board did you replace? I want to check mine to see what's installed. I only see one on mine and everything works as it should, aside from Darlingtons.

author: Jwillis
author_rank: Super Contributor
timestamp: February 26, 2024, 09:51:21 pm
content: I look forward to your video.

author: watchmaker
author_rank: Unknown
timestamp: February 27, 2024, 07:05:51 am
content: I changed the 10ohm that connects the paired emitters to ground to a 10K. Don't know why I did, but I first changed it to 1K and that cleaned up the trace. So I tried the 10K and not much difference.One error I made was that when I changed the zeners I used 5.2 V. I was starving the counter.It wants 1X leads. And I get clean traces.I think the Jameco PS kit I used does something. After a couple hours the BD 139 smoked. It ran nicely and after replacing the transistors, it runs nicely with a 2N2222 using my Instek GPS 4303 PSU.I am going to repower it with the Jameco to verify.It looks like it draws 60mA in low power. I have a line fuse, but I think I may put a 200 mA fuse on the secondary to help protect the circuit.It looks like there is a desire for this to do a meltdown under some situations. Given what you and I have seen, something gets unstable at times.I DID learn that the ICs are fairly bullet proof. Most survive the meltdowns.

author: Zada Moore
author_rank: Newbie
timestamp: February 27, 2024, 07:54:07 am
content: Firstly, ensure that your circuit connections are correct with no short circuits or loose connections. Then, double-check the specifications and polarities of all components. Sometimes, even minor errors can cause circuit malfunctions.Additionally, despite confirming the operational status of the integrated circuits and transistors through substitution tests, there may still be other components or environmental factors causing issues. Voltage fluctuations or excessive currents within the circuit can affect the components' performance.I recommend systematically troubleshooting the issue. This involves inspecting each component in the circuit one by one and using an oscilloscope to examine the waveforms at various nodes to verify if the signals are normal."I would advise following these steps diligently to identify and resolve any potential issues in your circuit.

author: watchmaker
author_rank: Unknown
timestamp: February 28, 2024, 04:14:50 am
content: The mods shown in YouTube were very beneficial. The photo shows the current draw (around 50mA) and the trace at 1mV per division vertical. Very clean. 2N222. I used an OP937F because that was what I had. Matched the 100K resistors in the base array and selected exacts for the amp, as measured w/ Shannon's Tweezers.It pays to buy bulk sales; I had everything including the prototype board and IC sockets.Whoever gave the hint about hot glue; thanks! I glued the standoffs and will locate the drill holes thru them. The closeup shows the two boards as they will be in my case. I sacrifice two Siglent probes to use for cables to the scope. Eliminates one more connection. Everything is wired with connectors for future mods and service.I do want to find some 100mA fuses to put on the transformer secondary to avoid a meltdown. I need to order a 4PTT switch and two test sockets for A/B comparisons. I took the OpAmp power from the holes left by replacing the 4 small zeners with 2 1W zeners. There are only 14 V rails, so higher voltage is not available for many transistors. But this is small and quick to pull out.Finally, there probably be a policy that prevents dyslexic people from working with DC. AC fine; but reversing pins and such creates things to fix. At least I am no longer afraid of CMOS ICs. I even reversed the input and output! I have to label and mark everything!Excluding the cost of the lab, probably spent around $125 for this.

author: watchmaker
author_rank: Unknown
timestamp: February 29, 2024, 12:56:10 pm
content: Thank you Jwillis for your support.The result is posted under Test Equipment.Turns out my rabbit hole may have started with a faulty trimmer pot in the Jaemco PSU. After 24 hours on my Instek with no smoke I looked at that closely. The 15v supply would randomly go down to 2 volts. This unbalanced the output transistors and burned them up. Replaced the pot and the PSU is now reliable.The Instrument OpAmp is a terrific addition. I have no idea why increasing the value on the collector resistor cleaned up the signal before I added the OpAmp.Now proceeding with the A/B function and labels. Found adhesive clear vinyl adhesive inkjet paper for labeling.With the banana jacks and 150mm leads, no noise or capacitance issues.Apologies for my faux pas.

author: watchmaker
author_rank: Unknown
timestamp: March 01, 2024, 12:24:09 am
content: For future readers:A careful reading of the original Elektor article ((December 1989) reveals two serious omissions on the ThaiKit.First and very importantly, this kit eliminated the switch at the 4024,pin 9. This enables switching from 8 traces to 4. The lower number of traces reduces the maximum base current to 75uA. This is critical for not blowing out high gain transistors like a BC550C.Secondly, the Shcottky diodes that were replaced by 4148s were there to protect the power transistors against short circuits.Finally, the high current output was NOT in the original ckt design. To make things worse, the Thaikit uses 7.5K resistors in this subcircuit which makes a 13.3 increase of available base current. What an odd scale factor. Replacing them with 10K resistors makes the increase amore natural 10X.I suspect the blowing out of Darlington pairs is the result of the top 4 current steps in the default ThaiKit setup that eliminated the switch at 4024, 9.

author: Jwillis
author_rank: Super Contributor
timestamp: March 01, 2024, 01:03:41 am
content: Quote from: watchmaker on March 01, 2024, 12:24:09 amI thought that the 7K5 resistors seemed to be an odd value. I'll have a look at those changes for high gain transistors. Very helpful. Thank You for your research.

author: watchmaker
author_rank: Unknown
timestamp: March 02, 2024, 12:49:44 am
content: Jwillis,All internal changes made. Switch at pin9 4024, 7.5K replaced by 10K and the 4148 replaced by ECG585s.The module on top uses the 15VAC we have to test Zeners. May make a true ramp generator with a 40V output. Down the road.I should get my two Ziff sockets tomorrow so that I can put this away.I will document all the changes and how I laid out the inside.No Ferrite Beads yet. Not sure I need them. Traces are on 700K depth.

author: Jwillis
author_rank: Super Contributor
timestamp: March 02, 2024, 05:45:09 am
content: I was looking at the 1N5819 which looks like the equivalent of the ECG585.Did you figure out the voltage adjustment with the 10K potentiometer ? I didn't quite understand what you wanted to do with that.

author: watchmaker
author_rank: Unknown
timestamp: March 02, 2024, 10:53:31 am
content: I think you are talking about the pot on the Zener module. That is a current limiter. The voltage is controlled by the pot behind it. I thought the Jameco gave me 25 volts total, but it is 15 v total across the full secondary.My Ziffs came last night. I will run the lines for them and find out if this changes my need for ferrite beads. MAry is going to make me labels out of transparent vinyl inkjet paper.I need to understand how to do the final calibration for the display of the steps. This has been a great learning exercise and your encouragement has been very helpful. Truth be told, I am almost sick of this project but I am driven (as in being chased with a stick) to resolve things I do not understand.I do think my education from the days of tubes helped me avoid some of the noise that can be realized in the ckts though.And yes, for some reason I could remember ECG 585 and not the 5819 which is what I actually used.I am ordering the VBA boards (5 sets) from PCB. Two are still not reserved. Let me know if you want one. Kind of unnecessary, but I am now interested in their execution of a curve tracer. More like Tektronix from what I understand.BUT, with our changes, this unit should cover most needs of amateurs. (In watchmaking, "hobbyist" is a pejorative which I despised. I knew amateurs who could run circles around supposed pros in micromachining and making parts)

author: watchmaker
author_rank: Unknown
timestamp: March 02, 2024, 06:08:22 pm
content: OK. Pics of the finished instrument with the exception of nice labels. Now with zener testing!Still no ferrite beads.

author: Grandchuck
author_rank: Super Contributor
timestamp: March 02, 2024, 09:56:55 pm
content: Quote from: watchmaker on March 02, 2024, 10:53:31 amAre those the boards with surface mount devices? I have been interested in building a better curve tracer but not up for a lot of SMD soldering.

author: Jwillis
author_rank: Super Contributor
timestamp: March 04, 2024, 08:00:39 am
content: Quote from: watchmaker on March 02, 2024, 10:53:31 amI managed to get a reading for Darlingtons, but to do this I needed to make another resistor diode array. I changed the diodes to 1N5819 and the resistors are 110K. I also had to change the 220K to a 470K. The 1N5819s make for a cleaner signal and the 470K lowers the amplitude of signal to the CD4024 counter which also helps. The problem I have is with the BD139 and BD140 complimentary emitter follower. It's going into thermal runaway. I added a larger heat sink but that only slowed it down but its still apparent over a period of time. Would adding a couple low value resistors to the complimentary emitter follower add enough negative feedback to eliminate the problem. I believe the 100nF cap is used as a bootstrap but it's not quite enough.I'll try to increase the frequency of the oscillator again since that seemed to help earlier. I put a 500pF in place of the 1nF but then changed it back.

author: watchmaker
author_rank: Unknown
timestamp: March 04, 2024, 02:02:57 pm
content: Quote from: Grandchuck on March 02, 2024, 09:56:55 pmYes, SMDs.

author: watchmaker
author_rank: Unknown
timestamp: March 04, 2024, 02:26:06 pm
content: Quote from: Jwillis on March 04, 2024, 08:00:39 amJwillis,This ckt is too damned idiosyncratic. I looked carefully at xraytonyb's videos and he obviously makes changes to his schematic and he does not show casing details.I have learned these details are important. For example, cutting up ribbon cable to avoid crimping results in very weird behavior. 20g hookupwire works well. Wire placement is critical. I employed what I remembered from tube days and ran my socket leads against the case; except for the collector switch to socket which is"in the air". (at the moment)Works well w/most transistors except those with some capacitance. See the pics below of a 2N5551.The sockets amplify the issue. The capacitance is there because when I use the 501A, I can see interaction at precisely the voltage that the sparks fly using ThaiKit.Another pic shows this gets worse when the front panel leads are hooked in at the same time the socket is used.Finally, the clean trace is the 2n5551 hooked straight to the leads.The socket wiring doubles the length of the "antenna". The leads are a couple mm from the board outputs.So I will eventually play with the socket output to switch leads. (all in the air or all glued to the underside or the top).The workaround for a/b of course is to use the 501A. But that is not the point.I will wait until I get motivated to switch the E and C jumpers on the right side of my sockets. No idea why I thought that was what I wanted (it WAS intentional) but at least I am not doing the calculations for space landings.Will this remain on my bench? Yes, to remind me to finish it. Will it stay there, maybe.However, I cannot suggest this as a viable thing for anyone who just wants a damned curve tracer. At $125 finished, and given the idiosyncrasies, the money is better spent on a Heathkit or 501A curve tracer.My shop is below grade in a rural area. I have no clue how this thing would respond in a noisy environment.But,I learned a lot. xraytonyb's explanation of the theory was worth the price of education. And I now understand there is nothing to fear about opamps and ICs, even if you cannot see a filament glowing.The VBA is next if I can get the correct order in!

author: cncjerry
author_rank: Unknown
timestamp: March 04, 2024, 07:32:48 pm
content: Where can i find the latest schematic? Was given one of these by someone when I purchased a large lot of components. I've never been able to get a really clean trace on a digital scope. But given what I see here, I was thinking about playing around with it again, but wanted to check the latest components. I have another tracer to compare it with.Jerry

author: watchmaker
author_rank: Unknown
timestamp: March 04, 2024, 07:58:36 pm
content: Quote from: cncjerry on March 04, 2024, 07:32:48 pmDo you want my revised schematic or the "new" original? I do like the opamp amplifier mod. It just occurred to me that I can also try wrapping my sockets to banana jack leads in Al foil (the tin hat solution).Also, I meant to add that I get the same calculated gain on this as I get with my 501A.

author: Jwillis
author_rank: Super Contributor
timestamp: March 04, 2024, 09:35:44 pm
content: Quote from: cncjerry on March 04, 2024, 07:32:48 pmWhat I did to clean up the messy trace was to wrap the Base line through a ferrite toroid. Just a few turns is enough. You can try this internally or externally on the Base test lead.Also changing the 1N4148 dioides on the diode resistor array sharpens the trace lines.Added PDF of manual and circuit diagram of Thaikits version.It works fine for most BJT's with low to moderate gains. High gain, especially Darlingtons, it can't because the drive current for the base is to high.

author: watchmaker
author_rank: Unknown
timestamp: March 05, 2024, 02:00:20 am
content: Thank you Alex and Jim.The tin foil did not work.JWillis and Jerry: Position is the key to happiness. Using the 2n5551 that displayed shooting stars:Below are pics of my socket wiring, overall wiring plan, the socket switch connector and the pudding.It still gives an oblique circle with the leads attached while using the sockets, but that is inconsequential really. I think it will stay on my bench for a while anyway. It is compact and will serve as an adjunct to my TCRL tester.Still, unless JWillis and Jerry can report success, I think this is too idiosyncratic to recommend.Dropping the socket board directly thru the top shortend the antenna and getting the leads into the air are the key I suspect.My wife got annoyed when these posts made me come back to the lab.

author: watchmaker
author_rank: Unknown
timestamp: March 06, 2024, 05:45:49 am
content: A Final(?) note. I went back to the 10 ohm resistor form the common emitters to ground. Back to sparks flying on the traces. A ferrite core on the collector wire was needed.Also, I think I know why the darlingtons do not like this tracer. On my 501A it took 20mA steps on theemittercollector to get a trace. This tracer works in uAs.

author: Jwillis
author_rank: Super Contributor
timestamp: March 06, 2024, 06:59:14 am
content: Quote from: watchmaker on March 06, 2024, 05:45:49 amThis tracer can't supply enough current to the collector. I did manage to get a TIP122 Darlington to work. But the current to the base needs to be reduced to a point where the gain of 1000 doesn't permit the Iceto exceed the supply current. Which as you say isn't very much. When it exceeds the supply current the voltage at the collector drops out. So to fix the problem, the power supply needs to be changed to allow for higher currents at the collector.Second problem is the voltage of the steps.The voltage of first 4 or 5 steps is to low to turn on a Darlington. The TIP122 for example need 1.4Vbeto turn on. So tracer only shows the last 3 steps active. The first 5 are bunched up at the bottom of the displayed curve trace. Still learning how the CD4924 works I suspect that that will have to be changed as well.I also noticed that on mine that the transformer is not 15V-0-15V. Its a 9V transformer. So mine was operating 3V lower than yours after regulation. Mine is working with 12V and not the 15V required. This happened because I didn't have a 15V transformer at the time and just put it together and to get it working. I completely forgot until the end of this thread to replace it.I did mange to stop the BD139 and BD140 from going into thermal runaway by adding negative feed back. All in all with a few hacks and changes here and there I could get it to work for a full range of transistors. But in the end I might just redesign the circuit and put it to a new board. Which would still be cheaper than the real thing and I might learn something new.

author: watchmaker
author_rank: Unknown
timestamp: March 07, 2024, 01:44:13 am
content: Thanks for correcting my mistake (emiiter>collector), I will do a strike through and correct it.I am not going to do any more on this. Without variable sweep voltage and selectable current steps, this is really an adjunct to the TCRL testers which can be used to A/B some transistors.A thought I had but will not execute is that perhaps running on set of lines from the board and putting the jacks on top near the sockets would reduce the coupling.But certainly, a ferrite core on the collector line between the jack and board output tames the beast.BTW, I want to reiterate that this unit gives the same Hfe as my 501A. And about 10% higher than my TCRL tester.I did get in a complete order for the 4 VBA tracer boards.

author: watchmaker
author_rank: Unknown
timestamp: March 10, 2024, 07:31:06 pm
content: In the tradition of fine bricolage, I now have a complete component center for the amateur. Curve tracer for matching small transistors, low voltage zener tester, and the TCLR tester in one compact unit.My wife made the labels for me from printable(laser or inkjet) adhesive sheets.Done and dusted.For higher voltage things I have the 501A, soon to be replaced by a VBA transistor tester (boards are on the way!!).If I had thought of this as a complete work station, I would have made room on the top for the TCLR tester. As it is, I mounted it using a door hinge.Its case is made from the material box. Bricolage!!!

author: Jwillis
author_rank: Super Contributor
timestamp: March 10, 2024, 08:12:24 pm
content: I LOVE IT!! Looks like one of Doc Browns Inventions.Glad you got it all working.