This gets even crazier when you want to see devices' overload characteristics and stuff. I build guitar pedals and vacuum tube sims using discrete transistor circuits. There are so many undocumented "effects" that I've learned about and used. I can say that math is great for when you are trying to nail down a specific design that requires precision. The art of using them creatively is a whole different level and it has taken me over 10 years to learn about and document a whole slew of things that aren't documented.
This is gold, love the deep dives as this usually, for me at least, makes things simpler. I know people always think abstractions are better for that, I guess they are when you want to learn fast, but I always struggled with that in school. Deep diving for sure made my homework go slow, but I understood stuff way better. :)
That definitely answers the transistor issue. Great to see this explained. Never heard about the Miller effect. Thanks for this ‘down the rabbits hole’ video.
Such a great hands-on guide to this issue I have been struggling with. Much of this is relevant with fet-based audio compressors from days gone by. Because the characteristics of the fet are what determine the some of the 'attitude' of the compressor, it is important to know how to find a modern match with similar properties. This now seems less daunting, thank Noel!
16:22 The small spike at the output right before the signal falls is also caused by the Miller effect: The input rises at that moment, and the rise goes directly through the parasistic capacitor to the output. The Miller effect amplifies the spike. After a very short delay, the MOSFET starts conducting and the voltage drops to zero.
@@airspeedmph Main reason is the retro computer renaissance, there is so much happening around the Commodore 64 and other retro computers these days that consumes a huge amount of hobby time. Some time ago SteamOS and gaming on Linux was brand new so that was where I was spending my spare time on. But currently... nothing less than wonders are happening on computers I love and I want to enjoy this.
@@danielmantione Totally get that, I spend my time alternating the two (Linux and retro) although I have to admit that the retro part I'm only experiencing vicariously through channels like this, since my only HW that can be called retro is a PS1 :) Lately I'm seriously consider getting real by acquiring some hardware, though I'm not sure where to begin. I'm somewhat inclined towards a Commodore 64, but a working one seem to be rather expensive. But yeah, is crazy what's going on in the retro space, new hardware+addons and even games, is impressive and alluring. And another thing that I especially find relaxing in the retro space is that everything is governed/motivated by passion, there's no in-fights, politics and ideology to be found here. Anyway, have fun.
The Miller effect is a multiplication of collector-base CAPACITANCE by the amplifier gain... totally different than base charge of a saturated transistor. A Schottkey diode from base to collector will prevent saturation. This trick is employed in 74Sxx and 74LSxx logic chips.
Very nice research on the transistors. Thank you for the effort showing the process! As for the 2nd edition of AoE, I recently said "What I learned from technical books: Contrary to popular belief they in many cases do not get better with revisions. It's often worth keeping earlier ones around." I'm glad I'm not the only one who found that. It's definitely worth it to keep older revisions.
Coffee in one hand, donut in the other and time to watch Noel's video. ps. wow. that was an interesting "eye opening" video. I didn't know about this charge build up effect on base.
For that particular transistor I have no problem: 1. I used to work for the manufacturer (Ferranti) 2. I have many ZTX312's and many other ZTX series devices from 45-50 years ago! 😱😳 3. I have several Towers' transistor selector books that detail the critical specs of the transistor and also give equivalents from that time (mid '70's!). I often find that modern equivalents quoted are actually NOT and finding an equivalent of the original equivalent works much better. 😎 Nice explanation of a really good approach though. 👍👍👍
Congratulations from Belgium for the simplicity of the explanation which allows everyone to understand without having studied engineering, thank you for sharing.👍😉
Awesome video. Very interesting but also easy to follow those of us without a background in electronics. I'd love to see some similar content looking at different types of capacitors.
The Z80 clock signal spec is more demanding than regular TTL and I suppose they could not integrate the driver on the gate array. The inversion is just a side effect and the gate array could have inverted it for sure, but the primary use of the transistor is to improve the signal. I forgot the details, but it was quite common to use a transistor to match the Z80 clock spec. Note that they used a 74HC04, not a 74HCT04 in the second revision, which is a hint in that direction as well. MOSFETs are a completely different technology than bipolar and while you can get lucky, the considerations to drive them are very different.
I don't plan to use transistors, even I don't have plans of working with electronics at this level but, oh man, I enjoyed this video A LOT! Your videos are always full of high quality material, presented in a way that everyone can understand. Great work!
A very humbling video! I recently repaired a friend's Commodore 1541 drive where a resistor went bad and had to use an equivalent NPN resistor. I thought I had done my homework right by comparing specs and it was a success, but you now make me realize I probably just got lucky! 😁
Brilliant, just the right depth. I always wondered how to determine the correct replacement transistor and this provides a great starting point. More like this please Noel!
This was so interesting it nice to hear that there still people who appreciate the retro computers enough to research find even small things that to make to make the whole system whole again for a new generation 😀
Very interesting, as I ran into this a couple of months ago. My NAD 5000 CD speler stopped working, and despite everyone telling me it was the transport (or laser), I didn't think so. It just didn't make sense. So I started reading, and found that after 25 years 2 transistors tend to burn out because they're not sufficiently cooled. So, I opened up the CD player and the burned spot told me that they were right. But then the search started.. Fortunately, in the end the local (well, 40 minute drive away) electronics store knew the player and what modern replacements WOULD work. And indeed, they did and it works like a charm again. But still, I was lucky there. This makes looking for replacements a bit easier... Thanks!
Thank you for covering this topic. BC547 is just cheaply made transistor intended for low frequency amplifiers and similar applications. There are also specialized high frequency transistors available. A metal can package was actually pretty popular in the past. For example, KC507 transistor, a BC547 clone, was produced in metal can as well.
Excellent video - this is why I love this channel, rather than just telling us the solution, you take us on the journey of learning and experimenting, showing both failures and successes (reminding that a failed experiment is also a succes, because you learned something new). It is really inspiring, thanks for that!
Big love for the deep dives here, never leave a problem unanswered, it's just too interesting having you track down the solution. Oh and your head planting the Art of Electronics book was a great shot!
Fantastic video, Noel! You're surpassing yourself. And I was delighted to see that you also had to battle the Bibl... err... the Sedra as an undergraduate. So did I! :-) Regarding the clock inverter, if the gate array uses the uninverted clock signal internally, it makes sense to invert it before passing it on to the CPU: the 180-degree phase shift helps account for, and even take advantage of, the propagation delay of the other signals shared with the CPU. The Atari line of 8-bit computers makes liberal use of this kind of phase shift to ensure proper synchronization between CPU and other active components, and it effectively doubles the speed of the system, since you get two clock tics per clock cycle, each in a different part of the system. Back in the day this kind of hack mattered. I also would be very careful about biasing any switching transistor without a base resistor. You got lucky (or perhaps you knew it) that the gate array had an internal pull-up. Otherwise the pin wouldn't be able to source the kind of current you get through a diode to ground, and the chip might have been ruined.
Thank you! Yes, the inverted clock signal makes a lot of sense. The thing that surprises me is that the Gate Array doesn't invert it before outputting it since nothing else on the board is using the uninverted one. I guess they either completely ran out of space in the GA or it was a "fix" they had to do afterwards.
@@NoelsRetroLab That was probably because of a limitation of the specific process technology used in the gate array, which may have prevented either enough buffering capacity (i.e. cannot drive or sink enough current) or fast-enough switching at the required current. It surely makes sense. An external transistor can use very different process technology than logic and can have larger die space than what could be done in the gate array.
My analogue electronics lecturers championed Sedra & Smith, and I was heading towards failing the course... Then one of my classmates showed me his copy of The Art Of Electronics, and suddenly everything was alright. =)
Good video. I'm not much of a hardware person, but am picking up a bit these days thanks to you and others working on retro kit. This was a great insight to transistors, which I was always a bit scared of in my distant youth. You are very skillful at explaining things, you have the ability to get into detail, but still keep it enjoyable enough to carry on watching - something my old statistics lecturer was sorely lacking! I also like that you want to know why things work, or don't work. Some would have just found a solution and moved on, likely to be something I would do. But your curiosity has given us another great video.
The book 'Art of Electronics,' in Polish known as 'Sztuka elektroniki,' is excellent. It contains a lot of content and is easy to understand. I've been using this book throughout my entire high school, or as we say in Poland, 'W Technikum.' :)
I'm more into microcontrollers etc than retro stuff (although I do have a great nostalgia for the 8-bit days)... so this video was really really useful... more useful than some of the electronics channels... thanks!
That was a fantastic video! It had meat on it's bones and you explained it in a very clear manner. Coincidentally I also had to find some modern replacement transistors for a board I've been working on. I loved the experimentation, keep it up!
I *just* encountered this delay effect with a transistor circuit a few days ago. I solved it by replacing the transistor with a different part, but now I know I can add a capacitor or read TAoE. Thanks!
This topic is really not popular but very useful, I have some retro cards laying around, and some components are not in production anymore, thanks to Noel which dig deep in the topic.
In the past I once accidentally picked a BC308C PNP instead of a BC238C NPN for driving a ~20mA LED from an 74Nxx output. I wondered for several minutes why the LED lit up when the TTL output was low. Until I checked the printing again and noticed my mistake. But this wasn't just a PNP-NPN mistake, this also meant that the PNP had the C-E current running against its natural direction. The BC308C was still very happy and worked in other breadboard setups.
Looked at the datasheet for the ZTX312 and noticed that it specifies rise, fall and storage times - and the storage time is 13ns. The BC547 doesnt specify this, but a close cousin the 2N3904 does - 200ns! That explains why the speedup capacitor is needed. Interestingly I can't seem to find a common TO-92 transistor that has good switching times...
You have to be careful substituting mosfets because then the switching threshold becomes an issue - you have to raise the gate above the drain voltage by a certain amount to get the mosfet to saturate, whereas with a BJT you only need 0.6v, a MOSFET can often be up to 10V.
Yeah, I was really puzzled by the lack of timing info on the BC547. I wasn't sure if it was because it was fast enough for anything or just not intended for anything that you cared about timings. I guess it's because the answer wasn't a near number you can put on a table (and it would look really bad w/o the capacitor).
Try a 2N2222(A). It's a switching transistor, so its speed and transition times are optimized for switching. It is available in TO18 hermetic metal case with leads, a TO92 plastic case as a PN2222A, and SMD. Works for anything switching related below 300MHz. Check its spec sheet. Available everywhere and cheap (Digikey, Mouser).
Great video Noel. I had a similar issue when building my Sixty Clone with transistor in Q2. I eventually found one with help from one of the component suppliers, but at the time I thought a lot about transistor replacement for these replica boards.
Excellent work and thanks for sharing. I fully agree that older books are always good to have around. Was doing the same or similar experiments about a month ago.
Older books may have relevant information to restoring older electronics? Yeah that checks out to me and ironically maybe the best advice to people getting into this hobby that I've heard for a while.
This guy is awesome. I'm trying to repair an audio power amp - voltage regulators failed - no exact replacements available so seeing if alternatives can be used. 👍
I restore 2" broadcast video tape machines which are over 60 yrs old and work in the analog world. Compared to those beasts, digital is a piece of cake. I have to find transistors that match in many parameters, some even have to be matched as well because they are used in a balanced circuit. And in the analog circuits they must have a freq response from 30hz to 6mhz. When I was maintaining a complex digital device i thought as long as timing was correct and waveform was clean. I was good to go. Easy Peezy
There's usually several different transistors you can use as substitutes for most of the commonly used transistors, I've been pretty lucky with regards to transistor substitutions.
What sucks is when you are repairing motor drive circuits like an H bridge where one of the transistors is dead and made of unobtainium. Meanwhile a popular replacement is listed as close matching. In that case you get to rebias the circuit, or try to balance it. I fixed a 45 jukebox with a mobile player carriage. All I could do was one direction was normal speed the other was half speed. That is why I praise the use of common parts.
As you can see at the Oscilloscope the original Transistor does two things here: 1. stabilizing the square (so it is not overshooting etc). 2. amplifying it - as the gatearray does not output 5V (for whatever reason as well). So the transistor is just the cheapest version to implement it in a save way (to ensure that you always end up with a 5V square wave.
For the MOSFET you may have to tie the gate to ground with an additional high value resistor. The charge may not being pulled down fast enough through the IC. Especially since original design was a transistor.
I'm retired now and legally blind. But a great book that helped me back years ago was "Getting Started in Electronics by Forrest M Mims". It's free now as a pdf. For this 8 bit stuff it will help a lot.
Its a very true thing that many older textbooks often have more indepth information. sometimes as books have to add new info there sometimes is a removal of less sited stuff to keep the cost of the book in a certain price range or it might just be seen as no longer seen as useful. ether way, collect a few older books and store them, you never know
I searched in my old ECA VRT books (1996) and made a search for a substitute for the ZTX312 and found the 2N2369 and BSX20 between others as viable alternatives. I recommend the ECA VRT books for the purpose of search equivalent specially for old components.
I have done gain, hf, voltage, and amps. There are a lot of transistors with the same or 1 up that will work! Been using it since the beginning of transistors!
Ah yes. Good old electronics class. I think using a proper inverter would have made much more sense but they would obviously cost more. The revision was a wise route to take. The Miller effect is what deals with what is known as slew rate current ( the speed at which the amplifier can change it's output.)
Not quite. The slew rate is the maximum rate of change of output. In other words, it's the limit on rise time and fall time for edges in digital applications, and the frequency limit on large signal swings in analogue applications. In this circuit, the charge on the base capacitance is holding the transistor on (output low) in saturation for a period after the input signal goes low. This is effectively a propagation delay for the rising edge of the output, rather than a limit on its rise time. The fix for it when the input signal goes low is to find a way of sucking the charge out of the capacitance that the base of the transistor sees. If you have sufficient current sink from the input signal, then a capacitor across the current limit resistor will attempt to pull the base below ground when the input goes low and remove the charge on the base capacitance more rapidly, as shown with the BC547. If you have not much current sink, but more current source available from the input, then a low value resistor across the base-emitter (a "pull-down" resistor) will help to reduce the delay.
@@GORF_EMPIRE Don't patronise me; I'm perfectly aware of the Miller effect which is caused by the voltage gain of an inverting amplifier effectively multiplying the collector-base capacitance. The issue here is not the slew rate, which is clearly displayed on the rising edge of the output at 10:23 and can be seen to be around 5V in 200ns which equates to 25V/μs. The problem illustrated on that scope image is the 400ns that the BC547 takes to come out of saturation when the base current is shut off. That is entirely due to the charge on the capacitance as seen by the base having no low impedance path to discharge other than through the base-emitter junction. There is no Miller effect on a transistor _in saturation_ because a saturated transistor has almost zero voltage gain.
Those round bodied transistors are pretty common here in slovakia/czechia the local electronics manufacturer(Tesla) used that design a lot, even for OP, amps and some simple IC's
Years ago, when I still used transistors for prototypes, I considered that there were two types of BJT transistors: for amplification and for switching. Even when fast, the transistors for amplification were not suitable for switching (the 300MHz bandwidth for BC547 showed you that), what was needed was the switching time to be very low. I usually used 2N2222 for switching up to 1MHz and BC547 as amplifier. Never reversed them, because the results were bad, 2N2222 was not a good amplifier and BC547 was not a good switching transistor, (you saw it at 21:45). By looking at the datasheet, can see if a transistor is meant for switching applications, because there are few key parameters like switching time from low to high, from high to low, etc. You should have showed that in the video, not many people know how to read a datasheet.
I think Noels point was mostly to demonstrate that you need to do something extra to get the advertised 300MHz and this is valid for any transistor: A speedup capacitor will speed up a 2N2222 just as it speeds up a BC547.
@@danielmantione No, those 300MHz are one thing, they are valid in amplification. Make a amplifier, a oscillator and you will reach tenths of MHz domain, maybe hundreds, depending of the quality of the component. And he had this on his BC547. What he needed was the commutation speed that is give by the special construction of the transistor, (small capacities inside it, and others). And that was achieved with the transistor used in the original design without additional components. One can design a circuit, but to be replicate on industrial scale, the circuit must behave the same independent of the tolerances of the components. Noel said that, to fiddle with the components values in the BOM is not something that one will want to do when buy the kit to build it and enjoy it. The point he made (in my understanding) is that you must use the right component to achieve the desired goal. Only that he does not touched the subject I pointed out.
@@sebastian19745 GaAs FET's came out in the late 80s, often in a can w/ 4th gnd pin. Those things easily handled 600 MHz due to ultra low junction capacitance.
@@wiregold8930 Yes, but do you remember also theirs prices? One of these or a mosfet tetrode were quite expensive in 80s. Also, they were used mainly in RF, hence the extra ground pin. I got 3 BJT (BF200 or 214 I think it was, not sure) that had a 4th pin for ground, they were more expensive than a regular BC107/108, I did a 3 stage antenna amplifier with them. And they were pretty common by then, they were used in many TV tuners.
Fun interesting stuff. I subscribed ☺️. I haven't practiced electronics in over 20 years. I'm just now getting back into it. Been building my Electronics Laboratory Bench. Going back to school this year. It's not about making money it's about having fun 😊!
Love to hear that! I also hadn't done electronics in many years (focused on the software side), so it's been a really fun journey getting back into it.
Old now as I work through your videos. Most switching transistors have a Ton delay, Toff delay and storage time. High frequency transistors show the collector capacitance as well. The old CRT display base drive circuits for the line output stage were quite novel in trying to minimise storage time by reverse avalanching the base emitter junction to remove the storage charge as fast as they could. you would see a negative spike on the base of 15V.
Why it was done with the transistor first was probably more to do with how fast the CPC was developed (original designer went AWOL mid stream and total redo was done in months, I think KimJustice has a vid on it), be curious to check the Serial/manufacture date for the that board revision (or the one the replicant board is based off I should say). Future revisions obviously would have focused on redundancy aspects. Cheers Noel another great informative video and showing how to test for the defects is gold.
For a lot of transistors you are pretty much fine with using almost any one. Elektor had this sorted decades ago, using in their designs, which were made world wide, they had, for those general purpose transistors, the generic transistors TUN and TUP, standing for Transistor Universal NPN or PNP, which, as they published every year, a table of the 100 most common types of transistor per pinout, that would work in this application. Thus you could use almost any of the listed transistors, or pretty much any cheap commonly available by you transistor, and it would work there. Just choose the appropriate polarity, and the pin layout, and then you had pretty much free reign on the transistor. As to datasheet errors, depends on the pinout if it is being viewed from above, looking through the pacage to see the leads, or looking from down underneath, which flips the leads on it, though yes errors are often there, as the datasheets have been copied on and on from older datasheets with little checking, and often with OCR being used to grab the text, and then the graphs and images are inserted after losing orientation, or being flipped. Then no checks done, other than a random check that "hey no blank pages and sort of visible images and text" being there.
![ลองสุ่มไอโฟน 990 โกงมั้ย? [ โกงมั้ยครับ ep.101 ] | DOM](http://i.ytimg.com/vi/bfsWe0j492k/mqdefault.jpg)
This gets even crazier when you want to see devices' overload characteristics and stuff. I build guitar pedals and vacuum tube sims using discrete transistor circuits. There are so many undocumented "effects" that I've learned about and used. I can say that math is great for when you are trying to nail down a specific design that requires precision. The art of using them creatively is a whole different level and it has taken me over 10 years to learn about and document a whole slew of things that aren't documented.
This is gold, love the deep dives as this usually, for me at least, makes things simpler. I know people always think abstractions are better for that, I guess they are when you want to learn fast, but I always struggled with that in school. Deep diving for sure made my homework go slow, but I understood stuff way better. :)
That definitely answers the transistor issue. Great to see this explained. Never heard about the Miller effect. Thanks for this ‘down the rabbits hole’ video.
Hope he cooked the rabbit while he was there. :)
My first thought when I saw the slow turn off time was to clamp the Base to GND with a resistor, but then again I am not an electronics engineer.
Such a great hands-on guide to this issue I have been struggling with. Much of this is relevant with fet-based audio compressors from days gone by. Because the characteristics of the fet are what determine the some of the 'attitude' of the compressor, it is important to know how to find a modern match with similar properties.
This now seems less daunting, thank Noel!
16:22 The small spike at the output right before the signal falls is also caused by the Miller effect: The input rises at that moment, and the rise goes directly through the parasistic capacitor to the output. The Miller effect amplifies the spike. After a very short delay, the MOSFET starts conducting and the voltage drops to zero.
@Daniël Mantione I used to see you frequently on various Linux forums, not much lately, what happened?
@@airspeedmph Main reason is the retro computer renaissance, there is so much happening around the Commodore 64 and other retro computers these days that consumes a huge amount of hobby time. Some time ago SteamOS and gaming on Linux was brand new so that was where I was spending my spare time on. But currently... nothing less than wonders are happening on computers I love and I want to enjoy this.
I was noticing that spike and it looked severe enough that it could possibly re-trigger some circuitry at the wrong time
@@danielmantione Totally get that, I spend my time alternating the two (Linux and retro) although I have to admit that the retro part I'm only experiencing vicariously through channels like this, since my only HW that can be called retro is a PS1 :)
Lately I'm seriously consider getting real by acquiring some hardware, though I'm not sure where to begin. I'm somewhat inclined towards a Commodore 64, but a working one seem to be rather expensive.
But yeah, is crazy what's going on in the retro space, new hardware+addons and even games, is impressive and alluring. And another thing that I especially find relaxing in the retro space is that everything is governed/motivated by passion, there's no in-fights, politics and ideology to be found here.
Anyway, have fun.
Wow, I learned quite a bit here. Transistors are still something I get the basics of but not beyond, so this was really insightful.
I wish all electronics lectures were this good and this polished! Excellent work Noel ... thank you! 👏👍
The Miller effect is a multiplication of collector-base CAPACITANCE by the amplifier gain... totally different than base charge of a saturated transistor. A Schottkey diode from base to collector will prevent saturation. This trick is employed in 74Sxx and 74LSxx logic chips.
Very nice research on the transistors. Thank you for the effort showing the process!
As for the 2nd edition of AoE, I recently said "What I learned from technical books: Contrary to popular belief they in many cases do not get better with revisions. It's often worth keeping earlier ones around."
I'm glad I'm not the only one who found that. It's definitely worth it to keep older revisions.
Coffee in one hand, donut in the other and time to watch Noel's video.
ps. wow. that was an interesting "eye opening" video. I didn't know about this charge build up effect on base.
Glad you enjoyed it! I didn't know that either. I love it when I learn new stuff!
For that particular transistor I have no problem:
1. I used to work for the manufacturer (Ferranti)
2. I have many ZTX312's and many other ZTX series devices from 45-50 years ago! 😱😳
3. I have several Towers' transistor selector books that detail the critical specs of the transistor and also give equivalents from that time (mid '70's!). I often find that modern equivalents quoted are actually NOT and finding an equivalent of the original equivalent works much better. 😎
Nice explanation of a really good approach though. 👍👍👍
Congratulations from Belgium for the simplicity of the explanation which allows everyone to understand without having studied engineering, thank you for sharing.👍😉
Awesome video. Very interesting but also easy to follow those of us without a background in electronics. I'd love to see some similar content looking at different types of capacitors.
This video is filling the gap left by the previous one! It's very nice of you to delve that deep in this subject!
Never have I been more happy to have an OLDER version of a book. (My "Horowitz & Hill" is the Second Edition.) Thanks!
The Z80 clock signal spec is more demanding than regular TTL and I suppose they could not integrate the driver on the gate array. The inversion is just a side effect and the gate array could have inverted it for sure, but the primary use of the transistor is to improve the signal. I forgot the details, but it was quite common to use a transistor to match the Z80 clock spec. Note that they used a 74HC04, not a 74HCT04 in the second revision, which is a hint in that direction as well. MOSFETs are a completely different technology than bipolar and while you can get lucky, the considerations to drive them are very different.
I agree. I came to understand the Z80 clock input requirements designing a computer. Z80 is generally TTL level but clock is special.
I don't plan to use transistors, even I don't have plans of working with electronics at this level but, oh man, I enjoyed this video A LOT! Your videos are always full of high quality material, presented in a way that everyone can understand. Great work!
A very humbling video! I recently repaired a friend's Commodore 1541 drive where a resistor went bad and had to use an equivalent NPN resistor. I thought I had done my homework right by comparing specs and it was a success, but you now make me realize I probably just got lucky! 😁
It’s this kind of content that sets your channel apart Noel, love it. Thanks for putting the time into this video.
Transistor in the clock circuit is to adjust the high voltage level to what Z80 needs.
Brilliant, just the right depth. I always wondered how to determine the correct replacement transistor and this provides a great starting point. More like this please Noel!
This was so interesting it nice to hear that there still people who appreciate the retro computers enough to research find even small things that to make to make the whole system whole again for a new generation 😀
Thanks so much for the kind words! Glad you enjoyed it.
I hadn't heard the words "Miller Effect" in over forty years when you uttered them here. Wow... wotta blast from the past, man. Thanks!
Very interesting, as I ran into this a couple of months ago. My NAD 5000 CD speler stopped working, and despite everyone telling me it was the transport (or laser), I didn't think so. It just didn't make sense. So I started reading, and found that after 25 years 2 transistors tend to burn out because they're not sufficiently cooled. So, I opened up the CD player and the burned spot told me that they were right.
But then the search started.. Fortunately, in the end the local (well, 40 minute drive away) electronics store knew the player and what modern replacements WOULD work. And indeed, they did and it works like a charm again. But still, I was lucky there. This makes looking for replacements a bit easier... Thanks!
Thank you for covering this topic. BC547 is just cheaply made transistor intended for low frequency amplifiers and similar applications. There are also specialized high frequency transistors available. A metal can package was actually pretty popular in the past. For example, KC507 transistor, a BC547 clone, was produced in metal can as well.
This was amazing. Your deep dive was a great story
Excellent video - this is why I love this channel, rather than just telling us the solution, you take us on the journey of learning and experimenting, showing both failures and successes (reminding that a failed experiment is also a succes, because you learned something new). It is really inspiring, thanks for that!
Big love for the deep dives here, never leave a problem unanswered, it's just too interesting having you track down the solution. Oh and your head planting the Art of Electronics book was a great shot!
ON Semi: Producer of quality Semiconductors and Semi-correct datasheets
Fantastic video, Noel! You're surpassing yourself. And I was delighted to see that you also had to battle the Bibl... err... the Sedra as an undergraduate. So did I! :-) Regarding the clock inverter, if the gate array uses the uninverted clock signal internally, it makes sense to invert it before passing it on to the CPU: the 180-degree phase shift helps account for, and even take advantage of, the propagation delay of the other signals shared with the CPU. The Atari line of 8-bit computers makes liberal use of this kind of phase shift to ensure proper synchronization between CPU and other active components, and it effectively doubles the speed of the system, since you get two clock tics per clock cycle, each in a different part of the system. Back in the day this kind of hack mattered. I also would be very careful about biasing any switching transistor without a base resistor. You got lucky (or perhaps you knew it) that the gate array had an internal pull-up. Otherwise the pin wouldn't be able to source the kind of current you get through a diode to ground, and the chip might have been ruined.
Thank you! Yes, the inverted clock signal makes a lot of sense. The thing that surprises me is that the Gate Array doesn't invert it before outputting it since nothing else on the board is using the uninverted one. I guess they either completely ran out of space in the GA or it was a "fix" they had to do afterwards.
@@NoelsRetroLab That was probably because of a limitation of the specific process technology used in the gate array, which may have prevented either enough buffering capacity (i.e. cannot drive or sink enough current) or fast-enough switching at the required current. It surely makes sense. An external transistor can use very different process technology than logic and can have larger die space than what could be done in the gate array.
My analogue electronics lecturers championed Sedra & Smith, and I was heading towards failing the course...
Then one of my classmates showed me his copy of The Art Of Electronics, and suddenly everything was alright. =)
This was a really great and interesting piece of information, Noel! Well done!
Awesome video! Thank you for taking the time and fully deep dive into subjects like this!
Good video. I'm not much of a hardware person, but am picking up a bit these days thanks to you and others working on retro kit. This was a great insight to transistors, which I was always a bit scared of in my distant youth. You are very skillful at explaining things, you have the ability to get into detail, but still keep it enjoyable enough to carry on watching - something my old statistics lecturer was sorely lacking!
I also like that you want to know why things work, or don't work. Some would have just found a solution and moved on, likely to be something I would do. But your curiosity has given us another great video.
The book 'Art of Electronics,' in Polish known as 'Sztuka elektroniki,' is excellent. It contains a lot of content and is easy to understand. I've been using this book throughout my entire high school, or as we say in Poland, 'W Technikum.' :)
15:50 Hoorah! I'm happy you opted for fun. Deep dives into things we love are fun. Thanks, Noel.
I'm more into microcontrollers etc than retro stuff (although I do have a great nostalgia for the 8-bit days)... so this video was really really useful... more useful than some of the electronics channels... thanks!
Glad you enjoyed it!
That was a fantastic video! It had meat on it's bones and you explained it in a very clear manner.
Coincidentally I also had to find some modern replacement transistors for a board I've been working on.
I loved the experimentation, keep it up!
Great video! Thanks for taking the time to follow this one right through and then share it with us. Very enlightening!
I *just* encountered this delay effect with a transistor circuit a few days ago. I solved it by replacing the transistor with a different part, but now I know I can add a capacitor or read TAoE. Thanks!
I've really wondered about this topic myself. Great practical problem to explore this!
This topic is really not popular but very useful, I have some retro cards laying around, and some components are not in production anymore, thanks to Noel which dig deep in the topic.
In the past I once accidentally picked a BC308C PNP instead of a BC238C NPN for driving a ~20mA LED from an 74Nxx output. I wondered for several minutes why the LED lit up when the TTL output was low. Until I checked the printing again and noticed my mistake. But this wasn't just a PNP-NPN mistake, this also meant that the PNP had the C-E current running against its natural direction. The BC308C was still very happy and worked in other breadboard setups.
Looked at the datasheet for the ZTX312 and noticed that it specifies rise, fall and storage times - and the storage time is 13ns. The BC547 doesnt specify this, but a close cousin the 2N3904 does - 200ns! That explains why the speedup capacitor is needed.
Interestingly I can't seem to find a common TO-92 transistor that has good switching times...
You have to be careful substituting mosfets because then the switching threshold becomes an issue - you have to raise the gate above the drain voltage by a certain amount to get the mosfet to saturate, whereas with a BJT you only need 0.6v, a MOSFET can often be up to 10V.
Yeah, I was really puzzled by the lack of timing info on the BC547. I wasn't sure if it was because it was fast enough for anything or just not intended for anything that you cared about timings. I guess it's because the answer wasn't a near number you can put on a table (and it would look really bad w/o the capacitor).
Try a 2N2222(A). It's a switching transistor, so its speed and transition times are optimized for switching. It is available in TO18 hermetic metal case with leads, a TO92 plastic case as a PN2222A, and SMD. Works for anything switching related below 300MHz. Check its spec sheet. Available everywhere and cheap (Digikey, Mouser).
@@cjay2 I thought this too, but its storage time is still a rather large 225ns according to the Fairchild data sheet.
3rd Edition: The Art of Electronics
2nd Edition: The Lost Art of Electronics
Awesome video!! Using a real-world example as the motivation for this deeper dive into transistors really makes it easy to understand.
Great video Noel. I had a similar issue when building my Sixty Clone with transistor in Q2. I eventually found one with help from one of the component suppliers, but at the time I thought a lot about transistor replacement for these replica boards.
Excellent work and thanks for sharing. I fully agree that older books are always good to have around. Was doing the same or similar experiments about a month ago.
Fantastic video, thanks a lot. I checked the AoE 3rd ed book and found the Miller effect in Sect. 2.4.5
"Practical Electronics for Inventors" ! My favourite book (even more than "Art of.."). Great video as always!
Thank you, it was very informative. I again learned something new that I would never use in my life but what can I say, I love the learning part.
This was fascinating. Thanks for this.
Older books may have relevant information to restoring older electronics? Yeah that checks out to me and ironically maybe the best advice to people getting into this hobby that I've heard for a while.
This guy is awesome. I'm trying to repair an audio power amp - voltage regulators failed - no exact replacements available so seeing if alternatives can be used.
👍
I restore 2" broadcast video tape machines which are over 60 yrs old and work in the analog world. Compared to those beasts, digital is a piece of cake.
I have to find transistors that match in many parameters, some even have to be matched as well because they are used in a balanced circuit. And in the analog circuits they must have a freq response from 30hz to 6mhz.
When I was maintaining a complex digital device i thought as long as timing was correct and waveform was clean. I was good to go. Easy Peezy
There's usually several different transistors you can use as substitutes for most of the commonly used transistors, I've been pretty lucky with regards to transistor substitutions.
This is very useful. I'm not just saying that. Please keep making more component videos. Really helps. Great Job!
Wow. What a comprehensive video. Great information
The fact you stated about Base saturation made sense in switching times
You have taught me a lot about transistors that I didn't know before
What sucks is when you are repairing motor drive circuits like an H bridge where one of the transistors is dead and made of unobtainium. Meanwhile a popular replacement is listed as close matching. In that case you get to rebias the circuit, or try to balance it. I fixed a 45 jukebox with a mobile player carriage. All I could do was one direction was normal speed the other was half speed. That is why I praise the use of common parts.
As you can see at the Oscilloscope the original Transistor does two things here:
1. stabilizing the square (so it is not overshooting etc).
2. amplifying it - as the gatearray does not output 5V (for whatever reason as well).
So the transistor is just the cheapest version to implement it in a save way (to ensure that you always end up with a 5V square wave.
For the MOSFET you may have to tie the gate to ground with an additional high value resistor. The charge may not being pulled down fast enough through the IC. Especially since original design was a transistor.
I didn't watch the video yet, but I know it's going to be good and help me in my repairs. +1 Thumbs up !
Brilliant video Noel!
I'm still finding my way and a lot of this is miles over my head. But I learned a lot today watching this. Thank you!
I'm retired now and legally blind. But a great book that helped me back years ago was "Getting Started in Electronics by Forrest M Mims". It's free now as a pdf. For this 8 bit stuff it will help a lot.
@@Flatwoodsdad thank you very much! I will look that up.
Very informative. Thank you Noel
Excellent work! Really great deep dive on implementing the proper transistor for this application.
its always fascinating to remember all computers run on frequencies, just like electrons protons and neutrons spinning inside atoms.
Its a very true thing that many older textbooks often have more indepth information. sometimes as books have to add new info there sometimes is a removal of less sited stuff to keep the cost of the book in a certain price range or it might just be seen as no longer seen as useful. ether way, collect a few older books and store them, you never know
Where were you when I was in the Uni?. Oh man, another masterpiece from Noel !!!!
I suspect that this application would find the best replacement transistor by matching the emmitter-base capacitance as a priority. Nice video!
How interesting, depending on the model, the transistors can affect the signal that they can obtain at their output. great video Thanks
Excellent video, Noel. You have a great way of explaining things!
I loved this video. Thanks, Noel! This one will come in handy for years to come!
I searched in my old ECA VRT books (1996) and made a search for a substitute for the ZTX312 and found the 2N2369 and BSX20 between others as viable alternatives.
I recommend the ECA VRT books for the purpose of search equivalent specially for old components.
Fantastic video, Noel! Love these deep dives on electronics. You definitely are a great teacher.
I have done gain, hf, voltage, and amps. There are a lot of transistors with the same or 1 up that will work! Been using it since the beginning of transistors!
Great deep dive Noel... very infomative
Ah yes. Good old electronics class. I think using a proper inverter would have made much more sense but they would obviously cost more. The revision was a wise route to take. The Miller effect is what deals with what is known as slew rate current ( the speed at which the amplifier can change it's output.)
Not quite. The slew rate is the maximum rate of change of output. In other words, it's the limit on rise time and fall time for edges in digital applications, and the frequency limit on large signal swings in analogue applications. In this circuit, the charge on the base capacitance is holding the transistor on (output low) in saturation for a period after the input signal goes low. This is effectively a propagation delay for the rising edge of the output, rather than a limit on its rise time.
The fix for it when the input signal goes low is to find a way of sucking the charge out of the capacitance that the base of the transistor sees. If you have sufficient current sink from the input signal, then a capacitor across the current limit resistor will attempt to pull the base below ground when the input goes low and remove the charge on the base capacitance more rapidly, as shown with the BC547. If you have not much current sink, but more current source available from the input, then a low value resistor across the base-emitter (a "pull-down" resistor) will help to reduce the delay.
@@RexxSchneider It's still the slew rate. The fix for that is irrelevant. Look up the Miller Effect.
@@GORF_EMPIRE Don't patronise me; I'm perfectly aware of the Miller effect which is caused by the voltage gain of an inverting amplifier effectively multiplying the collector-base capacitance. The issue here is not the slew rate, which is clearly displayed on the rising edge of the output at 10:23 and can be seen to be around 5V in 200ns which equates to 25V/μs. The problem illustrated on that scope image is the 400ns that the BC547 takes to come out of saturation when the base current is shut off. That is entirely due to the charge on the capacitance as seen by the base having no low impedance path to discharge other than through the base-emitter junction. There is no Miller effect on a transistor _in saturation_ because a saturated transistor has almost zero voltage gain.
@@RexxSchneider Sure whatever pal.
@@GORF_EMPIRE Very mature.
a really good and instructive video thank you
Me devolviste a la facultad con este video. Espectacular la investigación. Excelente video! Gracias.
Those round bodied transistors are pretty common here in slovakia/czechia the local electronics manufacturer(Tesla) used that design a lot, even for OP, amps and some simple IC's
Years ago, when I still used transistors for prototypes, I considered that there were two types of BJT transistors: for amplification and for switching. Even when fast, the transistors for amplification were not suitable for switching (the 300MHz bandwidth for BC547 showed you that), what was needed was the switching time to be very low. I usually used 2N2222 for switching up to 1MHz and BC547 as amplifier. Never reversed them, because the results were bad, 2N2222 was not a good amplifier and BC547 was not a good switching transistor, (you saw it at 21:45).
By looking at the datasheet, can see if a transistor is meant for switching applications, because there are few key parameters like switching time from low to high, from high to low, etc. You should have showed that in the video, not many people know how to read a datasheet.
I think Noels point was mostly to demonstrate that you need to do something extra to get the advertised 300MHz and this is valid for any transistor: A speedup capacitor will speed up a 2N2222 just as it speeds up a BC547.
@@danielmantione No, those 300MHz are one thing, they are valid in amplification. Make a amplifier, a oscillator and you will reach tenths of MHz domain, maybe hundreds, depending of the quality of the component. And he had this on his BC547.
What he needed was the commutation speed that is give by the special construction of the transistor, (small capacities inside it, and others). And that was achieved with the transistor used in the original design without additional components.
One can design a circuit, but to be replicate on industrial scale, the circuit must behave the same independent of the tolerances of the components. Noel said that, to fiddle with the components values in the BOM is not something that one will want to do when buy the kit to build it and enjoy it.
The point he made (in my understanding) is that you must use the right component to achieve the desired goal. Only that he does not touched the subject I pointed out.
@@sebastian19745 GaAs FET's came out in the late 80s, often in a can w/ 4th gnd pin. Those things easily handled 600 MHz due to ultra low junction capacitance.
@@wiregold8930 Yes, but do you remember also theirs prices? One of these or a mosfet tetrode were quite expensive in 80s. Also, they were used mainly in RF, hence the extra ground pin.
I got 3 BJT (BF200 or 214 I think it was, not sure) that had a 4th pin for ground, they were more expensive than a regular BC107/108, I did a 3 stage antenna amplifier with them. And they were pretty common by then, they were used in many TV tuners.
👍 👍 👍 👍 👍 👍 👍 🍀 Great video! And very usefull for geeks who like to repair old devices... like me! 😜
Fun interesting stuff. I subscribed ☺️. I haven't practiced electronics in over 20 years. I'm just now getting back into it. Been building my Electronics Laboratory Bench. Going back to school this year. It's not about making money it's about having fun 😊!
Love to hear that! I also hadn't done electronics in many years (focused on the software side), so it's been a really fun journey getting back into it.
New thing for me is the Miller Effect, thanks.
Great info, and a great video Noel.
Old now as I work through your videos.
Most switching transistors have a Ton delay, Toff delay and storage time. High frequency transistors show the collector capacitance as well.
The old CRT display base drive circuits for the line output stage were quite novel in trying to minimise storage time by reverse avalanching the base emitter junction to remove the storage charge as fast as they could. you would see a negative spike on the base of 15V.
What an awesome timing, just as I need to find some replacement transistors :)
Why it was done with the transistor first was probably more to do with how fast the CPC was developed (original designer went AWOL mid stream and total redo was done in months, I think KimJustice has a vid on it), be curious to check the Serial/manufacture date for the that board revision (or the one the replicant board is based off I should say). Future revisions obviously would have focused on redundancy aspects. Cheers Noel another great informative video and showing how to test for the defects is gold.
I love the terminology used here. 😂
“Research-Rabbit Hole, Deep Dive” 👍
Great Genre too
Make Analog Great Again
God Bless.
Very facinateing and educational thanks noel.
great video nice story behind it to solve the problem
Great informative video Noel 👍🏻
This is some really useful information. Thanks!!
For a lot of transistors you are pretty much fine with using almost any one. Elektor had this sorted decades ago, using in their designs, which were made world wide, they had, for those general purpose transistors, the generic transistors TUN and TUP, standing for Transistor Universal NPN or PNP, which, as they published every year, a table of the 100 most common types of transistor per pinout, that would work in this application.
Thus you could use almost any of the listed transistors, or pretty much any cheap commonly available by you transistor, and it would work there. Just choose the appropriate polarity, and the pin layout, and then you had pretty much free reign on the transistor.
As to datasheet errors, depends on the pinout if it is being viewed from above, looking through the pacage to see the leads, or looking from down underneath, which flips the leads on it, though yes errors are often there, as the datasheets have been copied on and on from older datasheets with little checking, and often with OCR being used to grab the text, and then the graphs and images are inserted after losing orientation, or being flipped. Then no checks done, other than a random check that "hey no blank pages and sort of visible images and text" being there.
2:20 I didn't know this book. Thank you.
Excellent analysis on transistors... learnt a lot on this video! 😁👍
Good detective work.
Very informative, thanks for sharing your experience 🙂
Very interesting episode!