Hi Tony, Thanks for posting this video. Your modification to the Vbe matching circuit is inspired! I have to match signal transistors quite often when repairing vintage amplifiers. I don't have a curve tracer and have tried various methods. I built this circuit today and it really works well, confirming a good match for transistors matched for hfe and Vbe with my Peak Atlas DA75. I used a centre tapped 18v transformer which works fine. I love the fact that you can confirm matching on prolonged use and rise in temperature. Keep up the good work. I have learnt so much from your excellent videos.
Thanks for sharing this circuit, i plan to build one as well. Although i do have a Leader curve tracer, i actually built the kit one recently, and it does work quite well. Testing transistors under AC conditions is really ideal.I will add this one to my test bench. I enjoy your videos and appreciate your knowledge sharing. Greetings from Australia.
Thank you for the interesting videos re this Thai Kit CH-012 curve tracer. Along with a 7000 series Tek mainframe, I had a curve tracer plug in. In order to match transistors, I constructed a device using an 8-pin DIP socket wired through a DPST switch. The pin "holes" on either side of the socket were the "EBCE" holes (like on a DMM) and with two similar transistors mounted on both sides, switching back and forth allowed a comparison. The Tek mainframe bought the farm and the plug-ins were sold off, but I retained the device. When my CH-012 kit is done, the EBC connections will be wired to banana jacks on the front panel so I can use the matching device. This also somewhat addresses the danger of improperly inserting a transistor DUT as you mentioned in your kit construction video.
I have a pair of the trusty Tektronix curve tracers and they are a joy to use. Also, don't forget about the old school transistor testers that were made by many companies like Hickok, Westmore, Triplett, Sencore, etc. With the old analog meter style so called "laboratory" testers you can hand plot a curve trace on some logarithmic graph paper. I actually did that for years before I got my first Tek curve tracer. I can hand plot a curve with one of them and get a almost carbon copy match to what I will see on the Tek curve tracer. Also, some of the old analog units I have can supply up to 30 Amps so you can test high power transistors with them. I work in the RF world and it's nice to be able to test transistors at real world levels. I have seen the results from my Peak DCA75 fall flat on their face when I tested the same transistor under full rated load. It's surprising how much load can effect the hfe.
Full rated voltage that they will be working in if not a little bit over for some headroom, at the expected frequencies that they are expected to work with so a sweep through would also be great! I somehow prefer the older gear for being brutally honest...
@ 43:40 You could use a 10 pin ( 5 X 2) DIP socket for A and B component installation, and then from top to bottom go C-B-E-C-B, bridging the C and B pins on their respective sides where needed. That way, it would be easy to put just about any inline or round transistors into the socket with minimal bending to the pins. This would cover any one of 6 possible configurations quickly with minimal fuss. I am one of the many viewing this that will breadboard up a version, possibly making a gerber file for a board as well. Thanks for your time in thinking this one out and sharing it with us.
Definitely not enough discussion about this particular topic. This comments section should be thriving but it's not and that means that there's a lot of people who just match the part number... The thing with luck is that eventually it runs out and during the worst possible situation where the reason why the owner wanted his device repaired is because it has a set of transistors that are now unobtainium, so you can't touch them but the small signal transistors.... Ah ha! A cascading domino effect failure! Nice 👌
Very nice vbe circuit for testing transistors very simple discrete components you can't get better than that. I'm definitely going to make this simple circuit once. I always have said transistors are very important regardless of original or not original lots of technicians have said nah if the transistors the same number will be good enough but through experience I have seen lots of problems and it's not easy sometimes finding genuine transistors. Great video always with good explanation. 👍😁
The V_BE matching is all in all for differential amplifiers (like op-amp input stages) The mismatch is the amplifier’s offset error. Talk about microvolts! Another place where you depend on the match is a log-converter. In fact, then you need a match through a wide base current range. (In op-amps you operate at a fixed current, so you can do matching only at that current).
Aloha Tony, looks like a basic bridge circuit to me, but the application caused the smell of burning wood as I thought about it. Excellent thinking and I commend you for the circuit. I am already thinking of other applications.....Hmmmm
Small signal transistor matching is all about hFE. (FETs and valves are similarly matched for voltage gain.) In audio preamplifiers the transistors are biased so that they're in the middle of their linear range, and the circuit gain is limited to avoid clipping due to either cutoff or saturation. V_BE is a measure of where the transistor begins to conduct. For just about all small signal silicon transistors and diodes, this is 0.6V give or take a bee's dick, but any properly designed audio preamplifier will keep the base voltage well above this during operation. Matching for V_BE is pretty much a waste of time for your intended application; as long as your transistors are matched for gain, you're golden.
That misses an important point. Audio preamplifiers will often use a differential pair as the input, either to take a balanced input, or to allow negative feedback across multiple stages as is used in opamps. For a differential pair, the single most important matching parameter is Vbe because that determines whether the two transistors accurately track across a differential input voltage. Matching Hfe only matters for differential input currents, and most of the time that's far less important. Since a single parameter determines the relationship between Vbe and Ib, having two transistors with the same Vbe at a given current is a good indication that the parts match and will track as the current is varied.
Normal 100k have 5% tolerance, so you should use at least a 5k pot to compensate, you have to go fish for two almost identical 100k in the first place just to be able to use a 500 ohm resistor. How about changing the circuit to use a signal generator instead of the transformer, you could test them in higher frequencies more in line with where the transistors will normally operate.
Nice video Vf depends on the base current, just like it does for diodes. Just some nitpicking, hFE is not the same as hfe (and HFE or Hfe do not exist :-) ). So be careful how you write them down. It is one of the "h" parameters, hFE is the DC gain, this is what most testers measure. And not lineair(like you demonstrate on your CT), so if your tester uses 1uA base current the hFE will be different as when you use 10mA . hfe is the small signal gain. (The delta Ib versus the delta Ic) I have a bunch of old transistor testers , 3 of them professional ones and I have a Tek 576. All testers give a different value. Be careful with the old ones, some give alpha instead of beta. Your on/off time tester does about the same as my TRektronixs Type R plugin (transistor rise time tester) A rather rare plugin: www.pa4tim.nl/?p=3729 Edit: I was wrong, I think your tester is something different. (not T-rise, T-fall of the Vce, like the R plugin, yours is Vb ? ) Modern curve tracers are often called SMU's, source measure units I never heard about Vbe testing, is that an ¨audio-thing" There is a great book from Tektronix about curve tracers/transistor testing , they are from the 60-70's and as pdf on the www. They are called the concept series. See f.i. www.davmar.org/concepts.html
I think you need to protect the base emitter junction from reverse breakdown, most high gain transistors have very low reverse breakdown voltage usually 5V or less, this could potentially damage the transistors or might change some of the parameters or lifetime of the transistors. In your circuit you might connect two Zener (4.3V) diodes in reverse polarity in series and this whole arrangement is connected between the base and emitter of each transistor. This arrangement might adversely affect the measurement in high temperatures due to the temperature dependence of reverse current before breakdown of the diode.
I designed my own transistor matcher. It is USB based but the interface has 12 volt supply and supplies 0 to 45mA to the transistor. The PC screen can hold up to 5 different transistors at the same time for easy comparison. Those cheap matchers put about 2mA into transistor which is useless. I am working on a new version which supplies up to 1 amp to transistor.
As a happy owner of the initial version I'm happy to confirm its excellent performance - by replacing factory long tail input pairs with said tracer matched ones (Toshiba NOS 2SC2240BL), the DC offset on an integrated with no adjustment dropped from about 30mA to below 0.2 ! I hope Nigel gets his 1A version on the market soon and I'll definitely grab one to better match finals. The best piece of kit in terms of price to performance ratio I have in my clandestine, Dear Wife-proof workshop, by far. Thanks again Nigel !
I am always amazed what you are allowed to drive on the road in the US. Where i live no vehicle is allowed on the road which has its tires be the widest part of the vehicle. Even if you have rims or tires being 0.5 inch wider than the body, the vehicle is confiscated and you are fined at least 500 dollars. You have to pay the towing fee and correct the vehicle. Then you need to have the vehicle checked and certified.(at your own cost).
On the curve tracer, shouldn't you also be using the data to plot Ib vs. gain? That way, you'll have a curve defined by seven points, and well matched transistors will follow the same curve?
No, the diodes are not current limiting. They clamp the collectors to a diode drop above ground (for NPN or below ground for PNP). That ensures that the Vce is around 1.2V to 1.4V (two diode drops), since the bases are at 0V and the the emitters are another diode drop beyond that. Their purpose is to minimise the dissipation in the transistors to lessen the effect of any self-heating from that dissipation.
Realy liked this circuit with a opamp socket and ac transformer 24 volt with senter tap give 12 volt 0 and 12 volt.?It seems to be what i need to match signal transistors.Wonder if i use i ac supply with variable ac to match output transistors would work.maybe another value on the 20 turn pot?this i am going to build a verson of.Very informative videos sir.
THT matched transistors may be very rare nowadays. SMD matched transistors were still a thing though. E.g. DMMT3904W (NPN) DMMT3906W (PNP) and NST45011MW6T1G (NPN)
Commenting on old video may be lame but the different reading from the Peak to the cheapie absolutely makes sense as both of them do measurement at different current. The Peak hat Ube 0.1V higher than the cheapie but the cheapie used 2.5 mA Base current for testing while the Peak uses 4.62 mA. So both are using different test point on the Ub/Ib curve (or Vb/Ib as you would have called it). I also have one of this cheapie-units with the rotational encoder and it seems to be pretty much consistent. I guess the different display of with/ without Ice-leakage could be because it is right at the point where it could not get proper reading for resolution reasons? And the Peak only did display leakage current of 0.01 mA resolution while the cheapie at least tried to have a resolution of 1 micro-Amps, that's factor of 10 inbetween. One thing is for sure: The cheapies may not be lab-grade accuracy but according to my experience they give a pretty good idea of the device under test. Especially as you won't compare the transistor measured with one device with the measurement on some completely different. You will all measurements against the same meter.
I wonder if the testing parameters change if you run the tester at a slightly higher voltage? I also have been using one of those cheap Chinese devices and it's pretty good at what it can do... Surely it should be able to handle 10V or 11V. I don't know but it got me thinking when you mentioned above about the different voltages an current that each tester used, unless the test parameters are regulated? Who knows.
@@PeterMilanovski The cheapies are usually using the A/D converters of the Atmega AT328 microcontroller without much of protection circuitry around it and that converter has a limited range of input voltage only. So, I don't think it's a good idea to work with much higher voltages. The ATmega328P is having maximum operating voltage of 5.5V and all input ports have to stay even below the power supply voltage or you may damage the microcontroller. On the other hand, if you are measuring some (bipolar) transistor it would not affect the measurement that much, as that would amplify the *Current* but not Voltage. It's something totally different for measuring break-through voltage of some Zener Diodes or LED's or Thyristors..... But - it is a cheapie! It won't give you all the truth about all components. It may give you some good idea of many devices, and the software really does a good job with current testers. But it neither is absolutely "exact" nor will it give you informations on all devices under test or even more give you all available informations on them. You will always have to take the informations being displayed with some grain of salt! ;)
@@Slartibartfas042 yeah I think that you are correct in saying that you would have to take the measurement with a grain of salt! I have a few different devices for measuring capacitors and they don't work with anything over 470uF, they give me numbers but I feel that I get better results with charging them to their rated voltage through a current analogue meter and if that cap is still showing micro amp's then it's not going to be used! I feel that leakage is a more important test than capacity most of the time but generally if it's leaking, then the capacity doesn't matter, it has to be replaced... It's an old way of doing things that hasn't failed me yet and the cheapie tester doesn't show you what it's doing during the test, let alone show what the device is doing while it's being tested, you just get the end result and don't worry about what was happening at the beginning or in the middle of the test! Things can get pretty salty some days LoL.
@@PeterMilanovski That's true, yes. Salty and sometimes smokey. ;) BTW: I doubt you don't know the youtuber channel and the video about capacity tester, but mayby someone else might be interested in it: "Mr. Carlson's lab" has some nice video about Capacity checking and leakage checking etc.: Just type in "mr carlson's lab capacitor tester" into youtube search field above - it's definitely worth a short look at it and I found that watching the series of videos there really helps to understand what is going on inside capacitors when they are aging (series Resistance, leakage Resistance)...
@@Slartibartfas042 thanks but I'm already familiar with Mr Carlson's Lab, he has a capacitor tester but it doesn't give you a good idea of what it's doing while it's testing.. I personally prefer the older equipment for that reason alone. I have no problems with the understanding of capacitors or any other components but testers and good one's are hard to find. I prefer to know what is happening at any time during the test so that I can make my own decisions... I have a really good channel to recommend, Steel Wheels Down. The best explanation for how a transistor works on the planet, once you see the video, you will understand how a transistor works better than most, his other videos are really good too. Sadly he's no longer with us, he had cancer! His last video is sad because you can see that he knows that he hasn't got long. He is probably the best teacher that anyone has ever had... Check it out if you haven't already..
The Vbe matcher circuit is very interesting. In cases you work with 1% resistors I would suggest to use a trimmer of 2 kOhm or 2.5 kOhm for pre-matching the circuit. 500 Ohm could be too small. Another point is the diode limitation of the collector voltage. The hfe of transistors as almost always smaller if you operate them close to their saturation voltage. In the data sheets it is typically given for Vce at 10 V and 1 V (see datasheet for 2N2222). Allready at 1 V hfe is considerably smaller than for 10 V. The last point was also the criticism I have relating the circuits in ianFritz-transmat0011_144.pdf from Ian Fritz, October 2010. My suggestion is, to operate with an adjustable current source delivering a constant current of more than hfe*Ib and a Zener-diode-like adjustable voltage limiter for 1 to 10 V for Vce in order to make sure that you have a more "natural" Vbe behavoir of the transistors under comparison. I personally work with a simple transistor tester in the first step to find hfe- and Vbe-matches. After this I operate the transistors in a test circuit which simulates the behavior in the application at the correct voltage and current levels.
Hello. What do you think about those sanken output transistor availability out there on some websites? I am trying some of them to be set up on my Yamaha p2201. Thank you very much and have a great day
I just use the transistor "beta" tester build into my B&K device tester. For a typical batch of 10 small signal transistors the Hfe may vary by +-20%. No need to measure Vbe. I've had good results with this method.
Good point, it really doesn't, since the transformer creates a isolation function. I'm sure its just force of habit for him to add something in like that to notes.
I'm building a Tester, hopefully nearly same like your's, got it as a DIYkit from ebay. What I would like to know is, what kind of cable are you using in your tester from the board to the case? The cable to the BNC Connector would be most usuarly coax. The Cable to the Transistor? Also coax to reduce any noice?
Check this video out ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-7exRUNCQ-hI.html It goes into a bit more detail on the Curve tracer and how I built it.
I enjoy your videos, Tony @xraytonyb . They are very useful to us audio enthusiasts. Just one question about this simple Vbe matching circuit: How good is it in real world conditions, for matching the transistors for differrential input pair of the amplifiers? I need to create a replacement of the monolithic differential pairs (uPA74V and uPA75V) in discrete variant, consisting of two thermally coupled single transistors. Is it enough to match them with only this tester? You have many years of experience, so I think you can help me, because you probably had compared the results of the same two transistors paired with this tester with the results obtained with curve tracer. Thanks in advance and greetings from Serbia.
I’ve got the Peak Atlas DCA55 - best money I ever spent; though mine has a black case, rather than a blue one. I’d recommend this to any electronics tech or hobbyist into designing/testing/salvaging solid-state electronics. Sadly, there’s no easy way to test SOT-23 package devices; the clip leads are just too big and unwieldy for this. 😥
this test matching circuit you build/thinkering with. ac transformer with senter tap 3k3 resistor couple of diodes a socket and 2 100k resistor and a 20 turn bourns vr pot etc.Would it make it better be a good idea if the ac frekvens could be variable to?.Or is it one spesific value that tells that a pair of transistors are matched over a wide range frekvensy.For me audio range is importent.
No, you are only going to get the frequency that you already have in your AC power socket at home. I understand what you want, to have variable frequency, it's going to be more complicated! You will need a function generator, if the function generator has the sweep ability with adjustable sweep speed, that would be even better, the generator will have to control a transistor which is going to drive the test transistors. It's much more complicated but it could prove to be useful, especially if you use a variable power supply, that way you can test at or above the voltage that they are going to be working in and also sweeping through all the frequencies that they are going to be expected to work with. That would make a really good real world test... All the voltage would be there, the heat from working with be there and the frequencies will also be there, you just need to see if anything changes over the frequency range and time as they heat towards their operating temperature! Nice 👌 But who's going to make one? A function generator that has the ability to sweep with starting frequency and ending frequency, forward sweep and backward sweep, not cheap! I don't know of any cheap good quality low noise Chinese generator that has those features... Sweep is very important for audio work...
That's the one I was talking about when I said Atlas had a USB model. Although I haven't tried it, it really looks promising. My Curve tracer can do a maximum +/- 10V and 2.3mA test on "high power" mode. The Atlas DCA75 pro can do +/- 12V and 12 mA. I also like the idea of the USB interface and software. If you connect via USB, you don't even need to use the internal AAA battery. I may purchase one in the future as funding permits! Thanks for asking!
No it won't. NPN transistors are being tested when one of the diodes is conducting (the positive half cycle applied to the collector side), and PNP are being tested when the other diode is conducting (the negative half cycle applied to the collector side). We're not testing both at the same time.
This is a question of circuit design experience. Usually you need matched transistors in differential amplifier stages and current mirrors. These are the typical circuits where matches of Vbe and hfe are essential to avoid offset and disproportionality. In many cases, especially if you don't need to go to the limits of voltage gain, there is some work around by use of emitter degeneration resisitors. This would be a nice topic for another video about the possibilities and limits of the use of mismatched transistors with emitter degeneration resistors in differential amplifiers and current mirrors.
@@t1d100 No, the schematic is correct. The diodes are there to reduce the voltage on the collectors to one diode drop above ground. For an NPN, the voltages are approximately: Vc = +0.65V; Vb = 0V; Ve = -0.65V (and the opposite sign for PNP). The idea of keeping a low voltage drop across the transistors is to minimise the power dissipation and hence the self-heating of the devices. With a collector current of about 0.1mA, that is irrelevant in this case.
Hi tony intresting vid i havean intrest in theTransistor checker and all so the PC software you wewre uesing i will sendyou an email thanks colin from scotland
