Let's Build A Simple Transistor Tester, Matcher , and Biasing Circuit.
Added 2017-05-18 06:09:37 +0000 UTCTwo simple, and very effective circuits for the design of audio amplifiers. Build these circuits and have a very accurate way to match, test, and bias both NPN and PNP small signal transistors, Germanium and Silicon alike.
Please note: Some of the resistors were not used in the parts list (2) due to a change in the supply Voltage. The test fixture Voltage was moved from 5 to 9 Volts during the production of the video, just to make things easier for those who may not have a power supply handy.
This is video #13, include this when requesting attachments.
Patreon NEW LIST of Videos: https://www.patreon.com/posts/8239565
Comments
This is excellent; I've played with electronics for many years and was frustrated trying to understand, especially transistors. I became frustrated with theoretical concepts such as holes and electrons, and this practical experience has really helped me. Thank you.
Joe Vaclavik
2026-01-08 01:14:04 +0000 UTCCircuit works great. First breadboard circuit I did right the first time. Thank you binocular microscope! Wasn't cheap, but worth every penny. I'll build a case for this and add a few switches and connectors for taking the resistances the easy way.
Chris Bennett
2025-03-17 23:25:41 +0000 UTCI understand the circuit causing the input and the output being 180° out of phase, but why does it lead or lag each other depending on whether it's a NPN or PNP?
Scott Morgan
2024-04-02 20:55:13 +0000 UTCNeat trick, thanks for sharing. I built a module with a potentiometer and a couple of resistors along with output Dupont sockets for leads to the circuit or DMM. Works like a champ! Only problem was the emitter capacitor. I ended up using a 10uF capacitor to get the best non-distorted output but only a gain of ~8-10 for the 2N3904 which is not too bad.
Sam Reames
2023-07-25 21:13:34 +0000 UTCBook learnin’ cannot equal the wisdom imparted by parts on the bench beside the breadboard. (some of those parts may have given their life to impart that wisdom😉). And you show how even the most meager ‘scope is priceless for teaching. Almost as valuable as a DMM, but not quite by a hair or two.
Mike O'Dell
2023-07-04 17:36:16 +0000 UTCMy eyes must be going, I put in a sine wave & get a square wave out. !!
Ron
2023-04-02 22:10:17 +0000 UTCHi Mr. Carlson I build the same circuit with 2N3904 on breadboard but it oscillating so much I have to add a 0.01uF cap from base to ground and collector to ground then all oscillation gone. Thanks I learned a lot from your videos.
Chinh Le
2022-10-20 19:15:58 +0000 UTCThank you
LoSaYa
2022-10-11 23:18:01 +0000 UTCThe AC128 took me 35 years back. I used to see that in old audio amplifiers. :)
Gahra Raschedian
2022-07-26 18:08:18 +0000 UTCIt is amazing how fast and deep your mind learns by watching these videos. I have been working with circuits for a while (For years, I used to repair them) but I could never design anything nor did I understand schematic. Now that I think about it, I don't even know how I used to do the repairs because I had no understanding of the signal, how transistors work, etc. But after just a few videos (all the videos from Paul on Youtube and just the few first ones on Patreon), I took a look at the schematic at the beginning of this video and all of a sudden, my mind went, "okay, so the signal comes in here, goes through the VR, ...." It is interesting that my mind can even trace the signal as I go through the schematic. I have no idea how that happened. That is very interesting and indicates how experienced Paul is and how well he teaches electronics here. Thank you Paul! Your time and efforts are really appreciated!
Gahra Raschedian
2022-07-26 17:29:47 +0000 UTCI would sure like to see a circuit board board for this device.
James Wood
2022-04-13 17:40:54 +0000 UTCA switching scheme like the one he uses for the capacitor outside foil tester would probably work well.
Ryan Dunbar W1RMD
2022-04-12 17:12:23 +0000 UTCThe written specs for transistors and other components all say the same thing, even though the ACTUAL testing results vary quite a lot sometimes with any component. There are certain exceptions to this if you want to buy graded components, but even then it's always better to check them where it really matters in a circuit.
Ryan Dunbar W1RMD
2022-04-07 19:12:36 +0000 UTCBrilliance + simplicity= Awesomeness! Incredibly valuable info + tool. Works great. Even using old computer monitor parts!
Ryan Dunbar W1RMD
2022-04-07 19:04:20 +0000 UTCDo you mean Negative feedback loop,s in audio amplifiers.Local negative feedback and or global feedback loop.If so,i Agree that it fix some problem like self oscillation over the audible frequency that can blow tweeters and amp.As for the best sound out of solid state i use power amp build with no local or global negative feedback,stable as a rock and it does not change the tonal character when volume goes up.They are the most silent amplifiers i have heard,even in high end price range give more hiss than the circuit i use better sound hard to find.My MM riaa also use no feedback loop,and that use 2 analog devices ic nr 1 is A.D744 nr 2 is A.D 844 opamps pr channel and a dc servo Texas Instrument LF 411if u want dual mono all the way,or 412 that take both channels.Better Riaa hard to find or build.You can search it as just MM or the one that have a MC stage in front of the MM. MC stage matched jfet power from a light bulb and photo cells pr channel that powers just the MC portion.i am trying to adapt the MM design as a mic pre amplifier.Look up LC audio on google or lc audio MM riaa or the long pcb with MC stage witch they still sell as a kit or finish.Circuit and why the design is this way etc you can read there.
Arild Tømmervåg
2022-01-24 03:46:59 +0000 UTCDid you ever make circuit boards for the two?
Timothy M Tapio
2022-01-20 03:16:56 +0000 UTCJust finished building your PNP in NPN transistor matcher. If you just match the betas of the transistors is that close enough without matching them by by using the circuits in this lesson?
George Seits
2022-01-03 00:11:03 +0000 UTCThis would be even more fun with tubes, just saying :)
Jay Cronen
2021-12-24 15:24:57 +0000 UTCI have had the worst trouble understanding transistors because everything looks backwards to me (grrr, conventional current flow). There was always something peculiar that I couldn't understand and it irritated me constantly. A 10,000 Watt light-bulb went off in my head after watching this video. I think I've got it now. Wow. Thank you, Mr. C!
Bob K
2021-10-13 21:28:47 +0000 UTCJust shows how right Harold Black was back in the days before transistors were thought of! (Hint: he invented negative feedback which alleviates these issues when it can be used - such as in op amps.
Marc Draco
2021-08-16 21:34:45 +0000 UTCI would also be interested in the answer
miaulon
2021-02-01 19:34:09 +0000 UTCAnother helpful Video, thanks a lot! I am not sure if I understand biasing correctly. Is it correct to say that biasing is finding the dc voltage for the base that keeps the transistor at 50% saturation?
Paul
2021-01-25 21:40:16 +0000 UTCAwesome!
Andrés Viana
2021-01-16 04:29:27 +0000 UTCMr. Carlson, great circuit. As I'm looking over the schematics for the NPN & PNP biasing circuits, they seem virtually identical. It seems that I can build it once and use a non-polar cap on the emitter, and a DPDT switch to select the flavour of transistor under test by reversing polarity. I also plan to switch the pot in and out of circuit for reading the bias settings. Have I figured it out, or did I miss something?
Steven Ruhl
2020-09-20 15:01:39 +0000 UTCUsing a 1 uF capacitor at the inlet (instead of 10nF) will give 100Hz 492mV, 1000Hz 985mV, 10kHz 1V. So there is a big difference at lower frequencies, but ofcourse not at higher and RF. Is there any downside at higher frequencies using too large capacitor at inlet to the amplifier?
Svein Arne Netteland
2020-04-28 06:00:28 +0000 UTC100Hz 6mV, 1000Hz 56mV, 10kHz 492mV, 50kHz 943mV, 100kHz 985mV.
Svein Arne Netteland
2020-04-28 05:57:17 +0000 UTCThank you for the feedback. Still, did a calculation with the amplifier (waiting with testing until I have the sine wave generator operational). If we put a 1 V p/p signal at the inlet the transistor will see the following voltage variation at its base:
Svein Arne Netteland
2020-04-28 05:54:35 +0000 UTCHi Svein. The answer is very simple, "Capacitive Reactance." This set up is a comfortable medium that allows a broad range of test frequencies to be used, well into RF.
Mr Carlson's Lab
2020-04-28 01:43:19 +0000 UTCNice setup for testing of transistors and biasing. One question is the use of 0.01uF (10nF) capacitor at the inlet and outlet. The inlet resistanse of the curcuit shown is in the range of a few kOhm's. The inlet section then form a high pass filter. The low inlet capactor cause a significant reduction in signal into the base of the transistor. The same for the outlet. Why not using much bigger capacitors (1uF or 10uF) to show the full gain potential of the transistor?
Svein Arne Netteland
2020-04-26 05:41:56 +0000 UTCMakes sense. I hadn't thought of the capacitor blocking the dc going back the other way. Thanks!
Curtis Roberts
2020-03-20 06:30:59 +0000 UTCYes Curtis. The transistor has to be biased on, in a class "A" style for the device to amplify properly. The DC bias is blocked by the capacitor, so it doesn't affect the previous circuit and vice-versa.
Mr Carlson's Lab
2020-03-20 06:28:23 +0000 UTCSo I've been trying to figure out the purpose of the biasing circuit delivering to the base and also having a separate signal input. As I understand it, the DC supply from the bias circuit is what is used to turn the transistor on. Then the signal passed through the cap rides on that turn on supply current and the transistor passes the signal. If the bias circuit was not there, the transistor would not be on all the time and the signal would not pass through properly. Is that close to basically correct? LOL
Curtis Roberts
2020-03-19 02:58:07 +0000 UTCYou should watch the video on the Maas Carillon driver, he covers how frequency is linked to certain gain states nicely in there.
Twobob
2020-02-05 21:09:53 +0000 UTCMr. Carlson, I just bought a Ballantine 1042A mod 49 oscilloscope. I'm having a hard time finding manuals, Can you suggest a web site please? Thank you
Wesley Howland
2019-12-28 23:41:39 +0000 UTCUsing this for audio, I tried simulating the circuit with the values of 14:53 and the AC analysis (LTSPICE XVII) is quite scary. The low end get swooped away completely and there is a weird bump at the high end. What would be the steps to take to make it nice and flat over the whole (audio) spectrum?
Trevor
2019-07-24 09:59:16 +0000 UTCYou're welcome Russ!
Mr Carlson's Lab
2019-05-22 05:37:33 +0000 UTCThis is an awesome lesson and a very useful circuit. It is exactly at my level, i.e. a near-beginner who wants to understand theory. Thanks, Mr Carlson!
Russ Sprouse
2019-05-21 17:20:11 +0000 UTCIt wipes off with alcohol real easy :^)
Mr Carlson's Lab
2019-04-14 03:16:15 +0000 UTCMr Carlson, I had a feeling you might regret printing that EBC PNP NPN directly onto your poor solderless breadboard! They will haunt you forever now! Haha
Bruce Dow
2019-04-13 23:05:20 +0000 UTCYou're welcome Jason!
Mr Carlson's Lab
2019-01-26 14:55:54 +0000 UTCLove this circuit. Built an NPN and a PNP version today on veroboard. I used milled headers so I can plug/unplug the pot easily. Thanks so much for sharing this :)
Jason Gill
2019-01-26 14:30:02 +0000 UTCHi Tom. Picture it like this: The transistor doesn't have to fight the load (1K) as much as with a 2K resistor, so now its more of a Voltage amp. Keep in mind that transistors (unlike tubes and FET's) are current driven devices. They require base current, where tubes and FET's only require voltage (with extremely small current) Hope this helps.
Mr Carlson's Lab
2019-01-14 14:58:16 +0000 UTCHello Pual, and everyone (First post for me) I took my time and try to understand and create everything in this great lesson. I do not understand the following: Why (And i verify that with the oscilloscope) when i change the value of the Collector resistor from 1K to a higher value i am getting more gain ? When changing from 1K to 2K the voltage at the Collector changed from 2.25V to 1.3V. I am missed something with the transistor logic, as i don't understand this. Thank you very much ! I really enjoyed this lesson. Tom
Tomer Granit
2019-01-14 00:05:16 +0000 UTCThanks Paul - I'm might cobble something up and see how many light-years away from your design I get ;-)
Paul Pruss
2018-10-14 02:10:36 +0000 UTCHi Paul. I left the design to the breadboard at this point. Down the road I will design a test fixture with sockets and a readout. This will allow for exact biasing for transistors.
Mr Carlson's Lab
2018-10-14 01:52:05 +0000 UTCA bit late coming to this project. Was there any progress on the circuit board design? I'm guessing that you would need to have some kind of component "header" soldered to the PCB to allow for the Base connection, swapping out of the pot and biasing resistors and possibly the Collector resistor (NPN model).
Paul Pruss
2018-10-13 20:16:02 +0000 UTCThanks Paul. I can see this will be a lot of fun! Hopefully I'll be playing with it soon.
Robert Calk Jr.
2018-09-06 11:19:32 +0000 UTCThanks for the lesson. What scope are you using and how are you displaying it in the video frame? I like the simple, minimal display and would like to use a similar setup for other demo presentations in a beginning electronics class.
Jack Rubin
2018-09-02 21:46:25 +0000 UTCWow, this was a great lesson. That AC128 IS a very popular and now hard to find transistor amongst musicians used in early distortion (fuzz) effects for musicians. I’m fairly new to you patron best thing I’ve signed up for in a long time. Thank you so very much.
Jesse Cervantes
2018-08-16 02:05:31 +0000 UTCSir can you build soon a pretty cheapes ossiloscope? I think this kind of test gear is very expensive before or maybe now a days, right? I hope this is one in your mind to build this thing. Thank you!
Escabusa Roy
2018-07-08 11:42:24 +0000 UTCHi Roy. The scope is pretty important in this application.
Mr Carlson's Lab
2018-07-08 11:31:14 +0000 UTCI like it much with this transistors matches. Thanks mr Paul. I have a question in my mind, I know that the circuit is very simple but can I make this if I don't have an ossiloscope to see the sign wave for it is clipping or not?
Escabusa Roy
2018-07-08 11:21:47 +0000 UTCHi Greg. I didn't go as far as putting this in a fixture, but that would be a good idea. I look forward to seeing your design.
Mr Carlson's Lab
2018-07-05 09:16:39 +0000 UTC@ Mr Carlson's Lab Did you ever design a fixture for this circuit? I've been thinking about a few different things to add to the adjustment of the (possible) device as in a switched value for the collector 1k, 4.7k, 6.8k, 10k, for gain adjustment. Also, wouldn't the value of the emitter bypass cap value cause frequency change? Would leaving the emitter R value of 100R be fine? Or would that value be good to adjust as well? Many questions, but this device would be very benificial to effects circuit builders. I'm probably going to work on a device for this design (NPN for now) and I'll share once completed!
Greg Braun
2018-07-05 02:09:21 +0000 UTCGlad to share Greg! You're welcome.
Mr Carlson's Lab
2018-06-27 20:22:01 +0000 UTCOhhh goodness.. This is going to change my whole process to building circuits. THANK - YOU!
Greg Braun
2018-06-27 08:40:18 +0000 UTCThanks for taking the time to write Roger!
Mr Carlson's Lab
2018-06-15 11:33:58 +0000 UTCHi Paul, I built the bias NPN circuit, but a little different, I had no 100K pot, only a 50K. I used 47 + 22K from supply to pot, then 4.7K from pot to gnd. Checked bias w/ DMM, best output always w/just over 0.6 v between base and emitter. First 9, then 12 V used for the supply. Started with 1K for the collector, later 2K. Base circuit remained the same for now, w/ .01 uf for in and output. 56K from output to gnd., looking for greater stability, Scopes = Elenco 25 MHz and Tektronix 453 50 MHz. Audio source = CXR Telecom 701B Telecommunications Test Set for audio, powered by 12 volt storage battery, that unit eats AA cells alive! Started out at -27dBm, but too low. Went to -16 dBm and all worked well, output still slightly fuzzy, wish there were a way to clear that up. Without a resistor at the collector, the transistors oscillated at RF frequencies with the look of "pinched off" modulation segments at regular intervals. I am so grateful that you have shared this knowledge with all of us, you have given me my first big tool needed to realize my goal, which is to design a discrete component broadcast receiver with the holy grail of 1uv carrier at 30% 1 kHz modulation sensitivity, with gorgeous hi-fi tone, with the option of narrow BW to tune in to so many stations next to 50 kW powerhouse stations here in New York City. I'd like tuned RF in the front end, 3 of 4 IF stages of amplification, and no transformers in the audio output circuits, to avoid bandwidth problems. Possibly a hi-fi chip might do. I'd like a ferrite bar of some 8 to 10 inches in length for best possible s/n ratio. I have no accurate with level indicator, low level RF generator, very little money to get a used one. Again, I am so grateful for the new knowledge that you've given me and others. Mike Rogers, KC2TOF.
Michael Rogers
2018-06-15 03:58:22 +0000 UTCYou got it!
Mr Carlson's Lab
2018-02-12 21:05:00 +0000 UTCWhat causes the 90 degree offset in the signal? The coupling capacitors?
Peter Sage
2018-02-12 09:45:56 +0000 UTCIt helps a lot, thanks again to Mr Carlson's. I watched a similar video long before <a href="https://www.youtube.com/watch?v=c6cmkm3UPUI" rel="nofollow noopener" target="_blank">https://www.youtube.com/watch?v=c6cmkm3UPUI</a>
Elvis Baketa
2017-11-16 21:01:15 +0000 UTCThe tool makes it obvious why substituting one transistor for another sometimes works and sometimes doesn't
Jeeptechfred
2017-10-19 22:45:50 +0000 UTCIt could actually be a whole bunch of things.. IE: Bias needs a slight adjustment, Input signal is too high, so on.
Mr Carlson's Lab
2017-07-30 15:07:28 +0000 UTCWhen looking at the output waveform, it looks to me like the negative portion of the sine wave tended to look "sharper" - i.e. the positive portion seemed to have a gentler curve at the peak than the negative portion (38:52 in the video seems to show this). Are my eyes deceiving me or is this the case, and if so what would the cause be? Nonlinearity in the transistor response?
Manuel
2017-07-28 23:08:04 +0000 UTCHi Jacob, poly or ceramic will work just fine for the signal path in the test jig.
Mr Carlson's Lab
2017-06-23 01:37:45 +0000 UTCHello Paul, After reading Zenwizard question I see your using a tantalum capacitor on the power rails. What type is being used for the input and output signals? When shopping for capacitors I find several types monolithic ceramic, polypropylene film, and tantalums not sure which to choose.
Jacob Leonard Fults
2017-06-22 16:37:45 +0000 UTCI created the NPN circuit in the app "iCircuitappdotcom" to see if it would work, and it appears to (for a sim, that is). Going to the COMMUNITY area to share screenshots and possibly the icircuit data file if anyone is interested in trying it. Don't think URLs are allowed here.
Stephen Martin
2017-06-14 23:23:55 +0000 UTCLOL, no problem Steve.
Mr Carlson's Lab
2017-06-01 23:00:13 +0000 UTCSorry about that, two many Pete's in my life. Thanks for the comeback.
Steve Crisp
2017-06-01 06:14:35 +0000 UTCPaul,
Steve Crisp
2017-06-01 06:12:54 +0000 UTCHi Steve, I think you may be addressing me? My name is Paul if so, I used to have a 2336 a few years back, with that little LCD display in the lid, but a friend talked me into giving it to him. That was a very nice scope. If you fix yours up, you will have a keeper.
Mr Carlson's Lab
2017-05-31 20:33:44 +0000 UTCHi Scott. The phase difference is due "mostly" to the .01uF input capacitor. If you swap this out for a 22uF, you will see the normal 180 degree shift. Transistors are current driven devices, and the capacitor chosen for this, is designed to be used at a wide range of frequencies. If you were to feed a 1 MHz signal to the input, you would notice a different shift (closer to 180). For testing purpose (and matching as well) the shift isn't a big deal, so I just left the input at .01uF.
Mr Carlson's Lab
2017-05-29 07:05:29 +0000 UTCHey Pete, Well I scored a scope and its on the way. Supposed to work good. Has a slightly damaged front face panel that I would like to replace when it gets here. If you or anyone out there has a face panel for a Techtronic's 2336 they would like to sell please let me know.
Steve Crisp
2017-05-28 22:22:08 +0000 UTCLove the explanation of how to find the bias of a transistor. Question: Why does the scope seem to indicate that the input and output signal are out of phase with one another. I would expect a single transistor in this configuration to invert the polarity of the signal, but the scope looks more like about a 90° shift. Is this just an artifact of you scope triggering differently between Ch1 and Ch2, or is there something else going on? Thanks.
Scott Morison
2017-05-28 04:03:15 +0000 UTCHi Jon, I can tell you this, you are going to really enjoy a video that's coming shortly :^)
Mr Carlson's Lab
2017-05-26 10:10:43 +0000 UTCGreat video! Do you know of any way of measuring heather to cathode leakage and microphonic tubes? Is that possible to implement in a tube tester circuit?
Jon Fredrik Våle
2017-05-26 10:02:01 +0000 UTCHi Hunter, about the "glitches" ... hard to say. Could be power supply noise or oscillation. If your breadboard has a metal back plane, make sure its grounded to negative rail. Add a bypass capacitor across the rails as well (tantalum type 4.7uF should work) The Radio Shack stores here in Canada have been gone for a long time now. They renamed them "The Source." Definitely not the same place. I do agree, it is kind of sad.
Mr Carlson's Lab
2017-05-24 01:17:05 +0000 UTCI noticed some glitches on the waveform, figured they were the charging/discharging of the electrolytic so I pulled the e-cap and sure enough a clean waveform but with reduced gain like you said. Later when I changed the value of the collector resistor to a higher value I noticed the glitches went higher up the sine wave. Can you expand on that? I can only guess that it changed the phase. I also pulled the vr, I had 12k and 80k plus the 1k already there. Thanks. I'm sad, radio shack closes in 6 days here in Baton Rouge.
Hunter carmouche
2017-05-23 02:41:23 +0000 UTCThats great Jurgen! Glad you repaired your drum machine successfully.
Mr Carlson's Lab
2017-05-22 23:04:35 +0000 UTCThank you Paul for this great explanation. I did not build the circuit but it helped me a lot troubleshooting my latest project (vintage drum machine /w germanium transistors and a faulty bias) .
Jürgen Driessen
2017-05-22 22:47:19 +0000 UTCHello Zenwizard. The capacitor on the rail is just acting as a bypass capacitor. (stopping unwanted oscillations due to excessive lead inductance)
Mr Carlson's Lab
2017-05-22 01:44:42 +0000 UTCOK, I noticed this so I am going to ask. In the beginning of the video there appears to be a tantalum capacitor on the power rails of the bread board hot to ground, when there is nothing else on it. What is that for? I am guessing it is smoothing out ripple from the dc supply?
Zenwizard
2017-05-22 01:41:10 +0000 UTCThanks for your input Silvio! Some good idea's there.
Mr Carlson's Lab
2017-05-22 00:24:33 +0000 UTCThanks for sharring, Paul. Waiting for prototype. Its a clever and useful rig to keep around my bench. Perhaps a simple VFO ( Colpits oscillator and a varicap diodes ???) in the same circuit could be useful to show frequency cut of transistors... Just think about. Thanks again.
Silvio Pinheiro - PU2SRZ
2017-05-21 23:08:32 +0000 UTCThanks for your kind words Mark!
Mr Carlson's Lab
2017-05-20 04:31:18 +0000 UTCI needed this in 6th grade. Seriously. I was deep in what I call Horowitz & Hill land. Your actual experience combined with academic knowledge puts you in the cat bird's seat for teaching. With some marketing, you will be a monster.
Mark Bosse
2017-05-20 01:14:31 +0000 UTCGreat!
Mr Carlson's Lab
2017-05-20 00:31:10 +0000 UTCHi Martin. DC Current gain (hFE) or "static forward Current transfer ratio" is a static measurement, not dynamic, so there is a difference with this test. AC Current gain (hfe) is a dynamic test, and is more suited for actual operation (of the device) So in short: Data sheets favor DC Current gain measurements, where as this is more dynamic. This test lets you see the result with the device in actual operation. Note: "AC Current gain," for a transistor like this is known as: "small signal, short circuit, forward Current transfer Ratio" .... A common term with the use of a curve tracer, representing AC Beta tests on data sheets.
Mr Carlson's Lab
2017-05-20 00:30:11 +0000 UTCThanks for your input Reb, it's always appreciated!
Mr Carlson's Lab
2017-05-20 00:14:50 +0000 UTCThanks Anders! Yes circuit capacitance will be an issue up there (1GHz) Looking forward to seeing your results!
Mr Carlson's Lab
2017-05-20 00:13:43 +0000 UTCHi Egil, I responded to Charles question as well. I'm very glad you noticed this... I was waiting for some of you to spot this and bring this up. Actually its too much, and too little capacitance within the circuit. The circuit drawn is tailored for higher frequencies (RF) to allow for more of a wide input range for testing. If one wanted to get rid of the phase difference (1 kHz input) you would do this: First, Parallel the input capacitor with a 22uF and note difference. Second, parallel the output capacitor with a 4.7uF capacitor and note the difference. Notice what's still present? Now remove the emitter bypass capacitor (100uF) and note the difference. You have now effectively tuned the circuit for lower frequencies.
Mr Carlson's Lab
2017-05-20 00:10:11 +0000 UTCHi Charles. I'm very glad you noticed this, I was waiting for some of you to spot this and bring this up. Actually its too much, and too little capacitance within the circuit. The circuit drawn is tailored for higher frequencies (RF) to allow for more of a wide input range for testing. If one wanted to get rid of the phase difference (1 kHz input) you would do this: First, Parallel the input capacitor with a 22uF and note the difference. Second, parallel the output capacitor with a 4.7uF capacitor and note the difference. Notice what's still present? Now remove the emitter bypass capacitor (100uF) and note the difference. You have now effectively tuned the circuit for lower frequencies.
Mr Carlson's Lab
2017-05-20 00:05:58 +0000 UTCThanks Phil!
Mr Carlson's Lab
2017-05-19 23:15:18 +0000 UTCEgil Hansen: I too noticed the phase shift was not exactly 180 degree and was curious as to why it was off. Paul, is Egil right that it is due to the capacitance within the breadboard?
Charles Legg Jr
2017-05-19 20:06:59 +0000 UTCPaul is there any correlation with the hfe dc current gain that is often quoted in the transistor spec sheet with what you see in a dynamic test like this. I seem to remember some of the old analogue multi meters sometimes had a transistor socket and hfe range?
Smiggy
2017-05-19 15:37:39 +0000 UTCPaul that's awesome. This is so much effort and knowledge you put in your videos. Many thanks! I noticed that you mentioned in the video that you're thinking about a kind of test fixture with connectors for EBC or CBE type transistor. I'd like to make a suggestion. All of your circuits and lessons are very modular. Having some kind of building block system in the future would be great. A base module that optional includes a small power supply (Voltage/Current adjustable) and a small simple signal generator circuit to start with. For those who have already a power supply and function generator, maybe there are only or in addition some input terminals present on the base module which shuts off the internal supply/function generator. At the top of the Base module maybe we have some kind of female pin connector or something like that which provides the signal, dc power, ground etc. to the attachable test fixtures like transistor biasing, or relay testing, curve tracing etc. The Fixtures can be made either on breadboard or perfboard/pcb. based on your course or by our own ideas. Maybe some day we share and troubleshoot useful fixtures, created also by the patrons in the community section... Again, thanks for the great work!
Reb Elba
2017-05-19 09:54:25 +0000 UTCSee, now another thought came... i have a B&K 501A curve tracer, i´ll build one of these in to this one with signal input so i can check actual cirquit to with different frequencys.... Again, thank you paul for excellent ideas
Anders "SM7HCE"
2017-05-19 08:40:55 +0000 UTCPaul - wonderful idea and setup :-), my old teacher kept on telling us in school ( 30 years ago ) that when designing multiple RF stages, you always will better of if you include a adjustable Bias stage. This little circuit has several functions that just came to my mind that i have´nt thought about... i´ll build this into a complete test set with surface mount and feed it with my signal generator, and see how far it will go in frequency with some filters attached... this will be very interesting to... i guess that up at 1Ghz and above one will face some interesting results with stray capacitance and oscillations :-):-), you are doing a great job with figuring out cirquits that will suit both the novice and the more experienced. 73´s / Anders..... Ps. i wont try and feed 1Ghz to a 3904 however.... :-):-)
Anders "SM7HCE"
2017-05-19 08:18:19 +0000 UTCHi Paul. Thank you for another nice circuit. I just wonder if it will also work for FETs as well (I'll try it out). I did notice that the phase angle between the input and the output was not 180 deg. I guess that is due to stray capacitancees introduced by the breadboard. In order for the circuit to be usefull at higher frequencies the final design must get around that problem.
Egil Hansen
2017-05-19 08:08:54 +0000 UTCGreat job, Paul! I had a long day yesterday but couldn't put off watching it. So, I watched it at, like 3 AM and thought I would have to pause at some point to continue later. Nope. It was too good to stop! Putting up the PDFs was a nice touch too...
nj Phil
2017-05-19 04:34:10 +0000 UTC7.2 was my limit so far. Haven't pulled the VR, do that this weekend.
Hunter carmouche
2017-05-19 03:04:48 +0000 UTCGlad you're enjoying Erik!
Mr Carlson's Lab
2017-05-18 22:16:24 +0000 UTCIt can get addicting. You may find yourself pulling them out of old circuit boards looking for the ones with the highest gain.
Mr Carlson's Lab
2017-05-18 22:15:54 +0000 UTCThey are getting pretty reasonable price wise.
Mr Carlson's Lab
2017-05-18 22:13:55 +0000 UTCThanks!
Mr Carlson's Lab
2017-05-18 22:13:17 +0000 UTCFor sure Mike. Leakage is often a result of breakdown within the transistor, this can be brought on by supply Voltage. If this is done, and you don't want to damage a good device, Current limiting is a good idea. Bad small signal transistors will show no amplification, or not bias correctly.
Mr Carlson's Lab
2017-05-18 22:13:06 +0000 UTCOh I agree definitely.
Mr Carlson's Lab
2017-05-18 22:09:42 +0000 UTCHi John, I will consider this when I have a solid planned item. I'm at the stage of "Cramming" So in short, trying to give the device as many features as may be needed.
Mr Carlson's Lab
2017-05-18 22:08:58 +0000 UTCHi Dale. You can post pix in the community section.
Mr Carlson's Lab
2017-05-18 22:06:45 +0000 UTCThanks Larry, a few "all nighter's" on this one.
Mr Carlson's Lab
2017-05-18 22:06:08 +0000 UTCIt all really depends on the circuit, and the way it was originally biased. There are many different bias schemes for transistors. Some circuits are not so dependent on bias either, determined if the transistor is operating in a linear region or not.
Mr Carlson's Lab
2017-05-18 22:05:21 +0000 UTCThis is the kind of stuff I like! What if you tested a leaky transistor, would you be able to test for bad transistors this way?
Mike Drzewiecki
2017-05-18 20:07:47 +0000 UTCthat is the best transistor test I have ever seen, but when you said matcher, I thought you were going to show us how to match to transistors. ah yeah, I'm sure I could test all day and not find two that are the same.
Michael Keffer
2017-05-18 18:54:55 +0000 UTCMr C, when you finalize the tester circuit, would you consider filing the PCB schematic with OSH Park, for example, OR offering them for sale, for those of us who are beginning in practical electronics and really don't have time to delve into PCB making (however interesting and challenging) any more than transistor making?
John Puma
2017-05-18 18:40:06 +0000 UTCWONDERFUL!!! You appear to have read my mind.
John Puma
2017-05-18 18:29:16 +0000 UTCGreat Paul, But having problem on the output wave form, not looking like yours.I am sending email Pix , trying to figure where I went wrong ..Checked all parts and location .
Dale
2017-05-18 17:37:39 +0000 UTCGreat Video,Learned A Lot,Thanks For All Your Hard Work You Put Into These Teachings.(:
Larry H
2017-05-18 15:29:19 +0000 UTCTransistors were always a sore point for me and I have tried searching the internet for results and I must say you have done a tremendous job on the explanation. One question though.... If you have a circuit and a Signal transistor has gone bad and you are replacing with an original. How can you determine which transistor bias to use? I would really like to know. Thanks for taking the time for these videos. Can wait to build this and do so testing.
Andre Gopee
2017-05-18 14:59:38 +0000 UTCabsolute amazing video!!!!
DAXweb
2017-05-18 14:12:11 +0000 UTCFascinating, very cool to see the relationships instead of just guessing. would have not thought there was so much variance between like components. thank you. looks like I for sure need at least a duel trace scope.
Steve Crisp
2017-05-18 13:07:47 +0000 UTCVery good explanation. Can't wait to build this and "match" some transistors.
Rob Bruno
2017-05-18 11:13:44 +0000 UTCExcellent ! Thanks
Erik G
2017-05-18 07:13:13 +0000 UTC
