Phase Inverters....for the Common Man

[@zeerust2000]

The great thing about Uncle Doug is that he tells you what you need to know and not what you, right now, don't need to know. I wouldn't be surprised if he's got a teaching background of some sort, because these videos are so well done.

[@UncleDoug]

Thanks so much, ZR. Yes, I was a classroom Math and Science teacher for many years.

[@mrwolfsang]

@@UncleDoug If I had a science teacher like you, I would have fell in love with it and became an engineer of some sort. Thank you so much for the video, I always learn so much.

[@UncleDoug]

@@mrwolfsang You're welcome, Wolfsang.

[@franky2shoes660]

@@UncleDoug Was going to say "all day long, uncle Doug has some kind of teachers degree". Thanks for everything, I have built a bunch of SE. Amps after finding an old line op. Westinghouse console and your youtube. Nice hotrod you have as well....PS attempting my first P/P amp today.

[@UncleDoug]

@@franky2shoes660 Thanks, Franky. Good luck with your project.

[@danweston6109]

My god man, i've been searching for this and you. Finally someone who understands what is going on and can explain it in a way normal people can understand. You're a rare breed Doug.

[@UncleDoug]

Thanks, Dan. I hope you enjoy all our videos :)

[@keithcoltron3171]

As an electronics engineer I still found this fascinating, Your description and explanations are just simply superb, I have tried on many occasions to 'teach' others but I'm afraid I just can't explain it like you, you just seem to explain things in a way that I'm sure anyone could understand, I knew what was coming next but still enjoyed it so much, it's the way you put things that makes so much difference and for people that want to learn it's an absolute must, being able to picture the process in your brain should turn anyone's light on! really well done and thank you for all you do, it's invaluable, if you haven't done any teaching in the past then we've all missed out! You're a star in a somewhat dark and otherwise confused universe.

[@UncleDoug]

Wow, thanks so much, Keith. I was a middle school math and science teacher for many years :)

[@keithcoltron3171]

@@UncleDoug Hi Uncle Doug, all I can add is lucky pupils, if you taught like this back then they would've had no complaints, at Uni the standard between lecturers was at times glaring, some were as bad as me (and that's bad!) It's just not my forte, some teachers just have that extra something and it makes learning an absolute treat so I hope things continue, I for one won't miss any as it's just so enjoyable, even if one already knows it's still a pleasure to listen, I hope that others will find you and your channel continues to prosper. There is unfortunately so much rubbish on KZbin which can have a negative effect and push people away, I just wish I could have a magic wand and do some frantic waving, I'm 74 now but still (given the right teacher!) love to learn new things, some may not stay embedded now though :-) but it's still fun, our profession is I think great to be involved with. From many more I'm sure here in the UK thanks again for all your time, effort, wisdom and patience, long may you reign, I'll have a quick word in her Majesty's ear and who knows a Knighthood could be just around the corner :-) Take care and stay healthy.

[@edwardkujawa]

you engineers all alike dont fix the stuff just design it maybe your different lolololol

[@SchecterMongoose]

As a trainer at my company; I can honestly say this guy is my spirit animal. The way he explains with a plethora of examples & metaphors reminds me of my teaching style. Awesome job sir; common language for the normie wanting to get started in Amp building / repair.

[@UncleDoug]

Thanks so much for the very kind appraisal, SM. That's exactly what we try to accomplish :)

[@JTM45100]

Your videos are a pure joy to watch. I'm addicted to them. I say this as someone who has probably 100 builds under his belt of various Era 100 watt Marshalls. I feel like I have a better understanding of push pull amps and the Phase inverter. Before I just knew what voltage should be, what my signal should look like, and trouble shooting methods.

[@UncleDoug]

Wow.....thanks for the very nice comments, JTM. Coming from someone with your experience, they mean a lot. I'm really glad that you find the videos to be helpful :)

[@nevenante]

JTM45100 , isn't great to actually understand the reasons behind our activities? For me it is hard to obey rules without understanding the reasons behind them :-)

[@UncleDoug]

Yes, I've always been very curious about how things "really" work, and very hesitant to accept most explanations......without some personal experimentation to verify them.

[@steveelliott4132]

i'd like to say thanks like the other guys i've been following along for a while and tonight it was nice and quite around here and i understood quite well about the single tube amps finally and was not sure about even trying to learn about the push pull amps but decided to go ahead and watch the videos anyway and i'm so glad i did it must have been my night and a little bit about the way you explained things (LOL) but i got it. It made perfect since to me finally man do i owe you dearly thanks a million keep it up cause without your explanations i dont know how long or if i would have gotten it and i know now i don't have to start with the smaller champ style amp i can go ahead and build the larger push pull amp witch is more what i need anyway your explanations are very clear and straight to the point if someone is strugelling i sajest they keep on watching the video's and it will come to them as i don't believe anyone could make it any clearer . again Uncle Doug thanks one more thing do you know of anyone who can be as clear on RF tube amps i know there are some differences and want to learn that end as well???

[@steveelliott4132]

p.s. for those of you strugling i sajest pay close attention to the rules one that helped me greatly is ac and dc can be walking down the same road over and over and never bother one another want affect each other at all one can go through some doors the other can't and vica verca but they can both share the same path at the same time without hurting the other and that amazes me but that is the one rule that blew it wide open to me thanks again Uncle Doug (pay no attention to my spelling or you will get no where guys)

[@jimviau327]

26:00 - Uncle Doug , I am an engineer myself and would like to let you know that, apart from some minor complicated details, your analogies are quite fine. In my opinion they are 98% accurate, which is quite remarkable. I think your best quality is to be able to represent some very complicated electronic concepts in a simplified way so that the electronic beginners could grasp the essence of it and start to understand. If a student pushes further his study, then the hidden details are going to reveal themselves anyway. Kudos buddy. Keep the good work, we like it.

[@UncleDoug]

Wow, thanks for the nice comments and excellent observations, Jim. I agree completely that the presentation to beginners has to be easily understood, then they will have a foundation to move on to higher levels of understanding.

[@andypendlebury6445]

Thanks Uncle Doug, I love watching your presentations. They are some of the most detailed and clearest examples I have found anywhere. I've read books, watched lectures, but I've learned the most from you. So Many thanks for that, it is well appreciated. Your'e a real hero for amp lovers. Best wishes!

[@UncleDoug]

Wow....thanks so much, Andy. That's great news :)

[@EricDobsonTV]

I’m going back and watching all the tech videos in order. They’re so insanely good. So clearly explained. They’re connecting a whole lot of dots I’ve picked up over the years from other sources. Thank you for making these!

[@UncleDoug]

You're welcome, Eric. We hope you both enjoy and benefit from the review :)

[@charlesshaw9090]

Hi Doug. Another very informative video for the DIYer. The size of the tail resistor in a long-tailed pair determines the basic gain of the phase inverter, PI. A large tail resistor gives a low gain PI but the inverting and non-inverting triodes would be balanced so could then have equal plate resistors. A small tail resistor will increase the gain of the PI but will introduce an imbalance in the triode gains. The inverting triode will have higher gain, 5%-10%, so to balance the triodes the inverting plate resistor is lowered to lower the gain, so restoring balance. 82k is usual but it actually lowers the inverting triode gain too much and so introduces its own, but opposite, imbalance. The distortion introduced by imbalance is very pleasant so equal plate resistors or 82k/100k both have a positive benefit. Some amps used 91k which balances well but sounds sterile. I hope this is useful.

[@UncleDoug]

Thanks so much for this very informative input, Charles. I, and other viewers, really appreciate it.

[@UncleDoug]

P.S. Your explanation is one of the clearest and most concise that I have ever seen. Thanks again.

[@silasfatchett7380]

It is possible to calculate the value of the inverting triode’s plate resistor which results in perfect balance in a long-tailed pair phase inverter (LTPPI). When the LTPPI was first introduced in the 5F6 Bassman with its 100k plate resistor on the non-inverting triode, this calculation resulted in 84k for the inverting triode, so Fender used the closest preferred value of 82k. The tail resistor was a relatively low value of 10k. As the value of the tail resistor is increased, it not only reduces the available output signal swing of the PI but also results in the ‘ideal’ value of the inverting plate resistor becoming closer to that of the non-inverting plate resistor. If the calculation is performed for the AA864 Bassman with its 22k tail resistor, it results in a value of 92k (which is closer to 100k than 82k), so 100k/100k would result in closer balance than 82k/100k, and 91k/100k closer still. As Charles points out, an unbalanced phase inverter encourages (pleasant sounding) second harmonic distortion in the output stage, so an amp designer can choose his preferred amount of imbalance, or simply copy the traditional 82k/100k combination (which is often the case).

[@matthewmartin9313]

Still coming back years later for a simple explanation. Also, im always impressed by your drawings

[@UncleDoug]

Thanks so much, Matt. In my early years, I wanted to be an architect.

[@markbunch5062]

Gosh, I've spent such a happy weekend with some of your videos. They are beautifully paced and pitched at exactly the right level for me. Thank you.

[@UncleDoug]

That's great to hear, Mark. You're quite welcome :)

[@ianbarker2599]

Hi Uncle Doug. You have just blinded me with the light shining from this video. Top bloke, Ta. Ian across the murky pond.

[@UncleDoug]

That's good to hear, Ian. Glad the video was illuminating :)

[@stevefiorito5379]

Excellent diagrams and clear instruction. Thanks.

[@johanwithag2432]

I saw a lot of YT video's on tube amplifiers. Yours are by far the best for understanding the basics of how tube's and tube amplifiers work. Thanks a lot for your efforts!

[@UncleDoug]

Thanks for the kind words, Johan.

[@baronsaari9878]

Thank you so much for these videos. I truly mean that. The fact you took the time to do all these drawings and have a clear easy to follow plan is just amazing. My hats off to you. Now if only I can find someone like you to do this on mic pres I'd be set. Thanks again.

[@UncleDoug]

You're quite welcome, Baron. Getting such nice feedback from viewers (like you) makes it all worthwhile. Rusty and I wish you the best !! ^. .^

[@kungfooo]

Doug: This is the first time someone explained the paraphase inverter in a way that I understood properly and now I get how this works in amps with two channels, one feeding the one side of the paraphase while the other channel feeds the other. I could not understand this before, but now it's very clear. Thank you.

[@UncleDoug]

You're welcome, KF :)

[@jlucasound]

If you are not, I hope this is taken as a complement. I am sure you know who he is. Master.

[@shaunsanders9673]

Once again, the fog lifts under UD's tutorial. I read everything I can get my hands on in order to learn more about amp design. Some of those books and articles are written by people who are clearly geniuses, and very, very good at math. But mostly, they confuse me further and further. UD is a ray of sunshine. Thank you, Uncle Doug. You're a teach par excellence!

[@UncleDoug]

Wow, thanks so much, Shaun :)

[@UncleDoug]

@Marco Guerini You'll have to do some searches on the Internet, Marco. I don't have a library of such books. Best of luck with your self-deucation.

[@perlgawker]

Hi Doug, Thank you for posting all these videos, sharing your knowledge and taking time to making these videos. I'm a guitar player and I want to know more about tone. Your video's about amplifiers and how they work are a very valuable resource for me as they provide great insight about what goes on in these tube amplifiers. Some day I hope to design and build my own amplifier. I know I am a long way from it because I don't fully understand everything yet (and therefore am rightfully fearful of getting zapped, or bit in my ankles by Rusty if he finds out i'm tinkering with high voltages without enough knowledge) but I feel you videos help me a lot in getting closer to achieving my goals on this subject. So once again: Thank you very much.

[@UncleDoug]

You're quite welcome, Niels. It's great to hear that the videos are helpful and informative. I encourage you to consider building your own amp....and I applaud your safety concerns. No one should "tinker with high voltages without enough knowledge" (very well stated), but that knowledge can be acquired through diligent study. Thanks for your very nice comments and best regards.

[@78tag]

These videos are perfect for people like me. I will never build or repair (some minor repairs) an amp but this goes a long way to satisfying my curiosity and will keep me from letting my lack of knowledge from overloading my butt when I do attempt any work on an amp. Just in case you are concerned about my skills, I know this much - use a wooden stick to touch components when checking for loose connections and don't trust anything to not have a charge if you don't want any nasty surprises :) :) :) Thanks again for your interest in helping all of us guitar fanatics. EDIT: I forgot to mention that you picked the perfect example for me, the Princeton Reverb, as that is the only tube amp I own or need.

[@UncleDoug]

Greetings, 78. It sounds like you have a good grasp of two very important safety rules :) I agree, the PR is all the amp that just about anyone needs.

[@kcrmson]

Don't try using "Let me center tap your output transformer" as a pickup line on the ladies, I just did and got slapped. ;)

[@UncleDoug]

+kcrmson I guess that's better than offering them a chance to see your ground lug :)

[@kcrmson]

+Uncle Doug hahaha, you win, you win

[@hippiekarl7]

+kcrmson That line caused a spike in ~resistance~

[@gyrgrls]

+kcrmson You want to insert your pole piece into her voice coil? Shame on you. That woofer really pumps...

[@oneofthemodels]

kcrmson hahaha that's pretty damn funny dude I'll have to remember that one!!!

[@jimkovacs7]

Thank you so much Doug, I am 63 and fixing vintage tuve gear in Venezuela for 40 years now... I thought I knew a lot, but your simple walkthrough definitely polished me off. Bless you, bro, for your insights...

[@UncleDoug]

You're welcome, Jim. Thanks so much for your nice comments. Best of luck with all your projects :)

[@jeffbrooks7246]

Thank you for "common man" explanations! Although I have a good understanding of electricity and electronics it seems any books dealing with tube amps and theory that I have acquired assume an engineering level of understanding and even if they start off with basic theory they seem to jump from that to the very complex too fast and I find myself either lost or bored from trying to piece it all together and not understanding why. Keep up the good work!

[@UncleDoug]

Jeff Brooks Thanks so much, Jeff. Rusty and I are glad our videos are helpful :)

[@PrinceWesterburg]

Thats crazy, it all makes sense - for 35 years I've carried the idea that push pull amps have a 'phase splitter', that one valve pushes and the other pulls with half the waveform sent to each - I always wondered why there wasn't a gap in the middle where diode lag killed low voltage signals! D'oh!!! All my amp builds are single ended as a result of not understanding this - except for my Marshall and the Radford STA-15 in my living room. Thanks for that, its all making complete sense at last!

[@UncleDoug]

I'm glad to hear that the video was helpful, Prince, and that your concept of double-ended amplification is now clear. Let us know how your first DE build turns out.

[@UncleDoug]

To Jay Blue: Your inquiry did not have a reply capability, so I will address it here. Hopefully you will see it. This is an example of the Paraphase Inverter, and is virtually identical to the inversion circuit discussed in my recent Rickenbacher Model 59 video. The signal leaves the plate of the upper 12AX7 stage, through the .05uf coupling cap, headed for the grid of the upper 6V6, but some of the signal passes down through the 220K resistor to the grid of the lower 12AX7 stage. In addition, some of the signal is leaked to ground through the 28K resistor, so that when amplified by the lower 12AX7 it will be of approximately the same amplitude as the upper signal, when it finally reaches the grid of the lower 6V6. I hope this all makes sense. Thanks for your kind words regarding my videos :)

[@sinecure45]

Ah yes, I do see the common structure to the two amps, though I note that you were first leaning toward a LPT interpretation. One wonders why such complications are introduced into a design--perhaps the design process is really just trial and error. Since I am planning to build a DIY of the YBA-2, I wonder if I could simplify the whole PI and power section without sacrificing tonal characteristics. Perhaps the gain in simplicity would pay off in improved performance. Would you care to comment on this proposition? Incidentally, I hope to use a power transformer from a Delta Blues for the DIY, but have yet to settle on an output transformer. The folks at Hammond have offered some suggestions in this regard. Any advice would be appreciated. If this is too off-topic feel free to shift the discussion elsewhere.

[@UncleDoug]

I wouldn't consider it a complication, Jay. It's a fairly standard style of phase inversion that was quite popular back in the late 30's and 40's. In my video on phase inverters, I featured it as one of the three types discussed. For some reason, perhaps fatigue or the fact that I hadn't seen one in a while, it took me a few minutes to pick up on it (in real time) in this video. If you want a simple PI, go with the cathodyne. All you need is the second stage of a 12AX7. Simplicity, however, does not necessarily equate with improved tone. You might want to watch my Phase Inverter video for some insights. Re the output transformer, the parameters are quite clear cut. You match the load resistance of the 6V6's, which is about 8K ohms on the primary side, and the secondary matches whatever speaker(s) you will use, 4, 8 16 ohms. Naturally, the primary must be center-tapped. I get all my transformers from Triode Electronics. I have also posted a video on Output Transformers that you should watch. Good luck with your project.

[@sinecure45]

Uncle Doug Many thanks for your comments. Right after the pole dance show I'll head into the transformer room for further enlightenment. Actually, I am much impressed by the logic of the long tail pair, and would probably consider switching over from the paraphase, at the very least in order to gain a tad more gain. I assume this would not upset the overall balance of the system. I guess it could be turned into a Deluxe as you show in the video. I too have sourced from triode for a champ project, and will check their offerings. Hammond may have something to offer, however. I just finished your expose of tone stacks, which was quite illuminating. Any chance of a discussion of active tone control?

[@UncleDoug]

The LTP is generally used in more powerful amps, like the Fender Bassman and Concert, and does provide additional gain, while the 5E3 Deluxe uses a cathodyne PI, and the 5C3 Deluxe uses the paraphase. Since the 5E3 came later, it's interesting to speculate if Fender considered the cathodyne to be superior.....or just slightly easier/cheaper to build (?) I had not really thought about an active tone stack video, primarily because the vintage tube amps I deal with are all passive, but it might be interesting. I recently encountered an ATS HiFi amp, as featured in my Garage Sale Bargains video, but it's been repaired and is long gone.

[@sinecure45]

Uncle Doug Given that the YBA-2 project is for a bass amp, I think that it would be desirable to extract maximum gain from the circuit, e.g., by switching the preamp 12AU7 to a 12AX7 and coaxing extra gain out of the phase inversion. Hence also my interest in active tone stack design. I suppose it depends on how much I am willing to risk on modding. After watching your rectification video I realize too that the YBA-2 does not have bridge rectification so the power transformer requires a centre tap. I suppose some efficiency might be gained by changing the rectification method.

[@TheDudesdad2000]

Once again I am pleased to have this video as a visual aide to identify the PI in a circuit. I have a new project with a rare Orrtronic Company tube amplifier, which was designed to amplify from four sources (tuner, TV, tape, phono). I presume it's rare, because there are only photos, and no other info, of this exact unit online from it's seller. It has a tube compliment of a 5Y3 rectifier, a single Mullard 7025, and two 6AQ5's in push pull. After thoroughly examining the schematic (lucky it was attached to the cabinet), and watching this video a number of times in the past and now, it looks like a long-tailed-pair phase inverter. Now time to dig in and get this one playing again. Thanks again Uncle Doug. Note: I was able to learn that J. Orr was responsible for the introduction of modern cassette tape material to the rest of the world, via German WW2 prisoners who had been developing the technology before and during WW2. But other than that, not too much to find online about this obscure amplifier.

[@UncleDoug]

You're welcome, Ted. Best of luck with your Orrtronic amp.....and thanks for the historical info.

[@Dan79istheman]

"I am such a fan!, cause' Uncle Doug is the Man!"

[@UncleDoug]

I thought YOU were the man, Dan.....but Rusty and I are very flattered. Thanks so much !!!

[@tubical71]

A cool shirt logo as well, may be on the back sinde of the -hopefully- ;) upcommin (!!) shirt, from the Tube-professor (next cool shirt name!) Uncle Doug!

[@brentgilbert4208]

I am LOVING your videos! I’ve learned more about electronics after watching about four of your videos, than I learned from three years of high school electronics classes (back in ‘69-‘72)! Old dogs CAN learn new (electronics) tricks!

[@UncleDoug]

That's great to hear, Brent. Keep up the good work.

[@tubical71]

For 12:40 You Nailed! Another side effect is that the output impedance of the cathode and plate circuit is not the same, in fact the cathode output impedance is much lower. So if you want to drive big tubes or some in paralell you need some extra driver stages, or you amp end up in doing "funny" things at high output levels...

[@UncleDoug]

A good point, TC. Thanks for bringing it to our attention.

[@brettni5698]

Good point, can you add some resistor to the cathode to match the impedance?

[@silasfatchett7380]

@@brettni5698 No, because the cathodyne requires equal plate and cathode resistances to produce equal (but out of phase) signals for the output tubes.

[@aaronatwood9298]

There are a few tricks to fix it, but then the simple cathodyne becomes way more complicated.

[@JagStar]

I watched this when you first put it out and did not get the long tailed pair at all. For years I just couldn't understand the workings of the long tailed pair, so I just trusted that it worked. I watched this again today and I totally understand it now. Interesting how years of doing can assist understanding. I think what a lot of people don't get, and this was my case, is that you can input a signal to the cathode. We are so used to seeing signal input to the grid that we have a block to understanding that signal can be input at the cathode too. Kind of like the old joke, "you can't get there from here". Thanks Uncle Doug!

[@UncleDoug]

You're welcome, JS. It's great to hear when a seemingly complex concept suddenly becomes clear. You made our day :)

[@JagStar]

😊

[@idogepgyar]

Nice explanation, really like you videos! Will you make a basic video about how to "decode" a schamatic step-by step? I mean how to read it, how to follow the audio signal and such. Thanks, András

[@johnmusico5839]

Cracked my head trying to understand how a cathode follower worked... nothing made clear till I saw this video...you deserve the Nobel Prize for 'Electronics for the simple person'! Many thanks!

[@UncleDoug]

You're welcome, John. Rusty and I will gladly fly to Stockholm to accept the award.....and the money that goes with it :) :)

[@treborheminway1196]

Anytime you get an electronics lesson combined with a Horse analogy from UD, you know that 1) its a good day. 2) your much less likely to forget the lesson. What a great teacher!

[@UncleDoug]

Thanks so much, Trebor :)

[@mikkabrightheart2268]

This helped me figure out why the channel volumes on the 5e3 are interactive. I built one recently and everyone on the internet basically says "these knobs interact and nobody knows why" ... Theres a rudimentary nfb loop thru the preamp stage on the unused channel... The cathodes are linked directly and the plates become more so as you turn up the volumes so the in phase signal on the cathode of the uses channel becomes the in phase signal on the cathode of the unused channel becomes the in phase signal on the plate of the unused channel and creates phase cancellations with the out of phase signal on the plate of the used channel I made a breakthrough in my understanding of amplification this morning and had to tell someone lol ... Everyone in my life goes all glassy when i start talking about amps... Also thanks for making this info available, your channel is an invaluable resource

[@UncleDoug]

Thanks for sharing your insights and joy of learning, Mikka :)

[@ramsaybolton9099]

Sir, you are a genius. Finally I understand why the signal is inverted at the plate when the control grid is driven. Thank you.

[@UncleDoug]

Thanks so much, I WA. Glad the video was helpful :)

[@stevenwilson3368]

I'm an electrical engineer and I loved this video. We never learned about tubes in college and I've never worked with them in my career. I generally understood the principles by which they operated but you have brought a greater fidelity to my understanding of how they work. Thanks!

[@UncleDoug]

You're welcome, Steven :)

[@lazomachavez-walton1549]

I'm one of those old electronics engineers schooled in the 60's and 70's. Your presentation is like what a master teacher would do to help none 'master' students understand. Reminds me of my old teachers at John A O'Connell Vocational HS in San Francisco back in the 60's. I really enjoy your style. I might even understand the Plate resistors on the long-tail PI now.

[@UncleDoug]

Thanks so much, LJ. We're glad the videos are helpful.

[@doom_siege]

A guy on Facebook had me sent here to help me understand tube amps, and I have been taking notes rewinding and learning all I can. Thanks for clear information in digestible form. I'm excited to keep learning!

[@UncleDoug]

Welcome to our channel, CJ. Best of luck with your self-education.

[@algio3041]

20 Years ago i had an interest in electronics and decided to go to school for it. If I had Just one ☝️ teacher that taught as well as you I probably wouldn’t have dropped out after a semester and a half. To be fair, I also could have benefited from having a better ethic, and being responsible.🤷‍♂️

[@UncleDoug]

Thanks so much, Algio. I too have suffered with ineffective teachers, and, as a result, tried to develop a style that filled in the gaps in their deficient methods. I'm glad that style works for you :)

[@claveduo8264]

I use to repair valve amplifiers and must say your videos are very well done: Simple, clear, accurate and your talking is so easy to understand for a non english speaker. Enhorabuena !

[@UncleDoug]

Thank you very much, Clave.

[@annomaus8386]

At last! Now I know why it's called a cathode follower. This is the first video or article in 3 years of searching that bothered with that very useful fact. Thanx Uncle Doug!

[@UncleDoug]

You're welcome, Chuck. We're glad the video was helpful :)

[@buntafujiwara3586]

I haven't watched this video for years. It was worth watching again. Thanks, Uncle Doug.

[@UncleDoug]

Glad you enjoyed it, Bunta :)

[@DVRproductions52]

Thanks Doug, for the life of me I could not figure out how that style of inverter worked with both cathodes of the 12AT7 tied together and seemingly nothing driving the grid of the bottom section. NOW I understand how it functions!

[@UncleDoug]

You're welcome, Dean. It's great to hear that the videos are helpful :)

[@AndJusticeForAll...1985]

I totally understand it, with basic electron flow understanding. I haven’t seen it explained so easily.

[@UncleDoug]

We're glad to hear it, TG.

[@phildiegidio4658]

Uncle Doug:............You have awaken the old Air Force tube jockey tech in me. I lost my way in the Solid State world and do very well to fix these types of Amps. Minus the high density stuff and multi layer boards that are impossible to desolder. Anyway......we are a breed from the past and will be missed. I am heading to retirement and am fixing amps to give them and the kids a second chance. Ebay is a great source of broken amps that don't take much to fix. Especially the Solid State stuff. You are my hero, and I greatly appreciate your no nonsense method of explanation. Thanks for bringing back my interest in tube amps. I still like the better frequency response of Solid State............but the harmonic presence of tubes is the real magic. You are the man. Phil from Philly.

[@UncleDoug]

Thanks so much, Phil. Rusty and I are honored by your kind words, agree with your comparison of SS precision vs tube "magic", and wish you the very best with your rekindled interest in tube amplification. Indoctrinate all the young people you can......so this art does not die out (with us).

[@jessecripps7830]

I agree with most sentiments on here...I've been trying to digest this information through studying schematics for many, many years and this video has finally delivered me unto a basic understanding. I'm very grateful and excited to move forward with my projects.

[@UncleDoug]

Thanks, Jesse. That's great news :) We're glad it was helpful.

[@edwardkujawa]

trying to understand whats on paper sometimes not the same theory versus practical application and what instruments t ue to diagnose problem in circuits some . instruments better than others{ I mean Test Instruments}

[@UncleDoug]

@@edwardkujawa Thanks for sharing, Ed :)

[@henryburt72]

Once again you came through! I am a newbie with 1 5E3 build and each time I discover another part of the amp that I have no idea about - I search for one of your videos. Thanks for demystifying more of the magic.

[@UncleDoug]

You're quite welcome, Henry. Best of luck with your projects.

[@zopilotesky3014]

Another outstanding explanation, this time regarding tube phase inversion. Books are filled with potential knowledge but there's no substitution for a good teacher. Thanks!

[@UncleDoug]

You're welcome, ZS.

[@robotsongs]

Dang, Uncle Doug. I've been watching your videos for years and years, and I've started and stopped this one several times in confusion. But I just came back to it again after another couple years and more study under my belt, and it made perfect sense and explained succinctly everything I wanted to know. Thank you so much for this gift! You're awesome.

[@UncleDoug]

That's great news, RS. It's always best to revisit troublesome topics and work your way through them :)

[@kolinevans9127]

Uncle Doug, I just want to say again you really shined a light on this for me , it’s like G0d sent some angel in a hot rod without a muffler to help us in phase peasants. Forever thankful.

[@UncleDoug]

You're quite welcome, Kolin. Our very best to you and yours.

[@seanjones9959]

Doug this really filled a few gaps in my knowledge. Simple verbal & visual demonstrations work best for me every day. I feel enlightened.

[@UncleDoug]

That's great to hear, Sean. Thanks !!

[@PierreKerbage]

Uncle Doug, you're simply awesome and one of the best teachers ever. Many teachers can use learning from you, meaning how you explain complex concepts and reduce them to understandable matters. Thank you. Fabulous sir.

[@UncleDoug]

Thanks so much, Pierre. We're really glad to hear that you enjoy our videos.

[@r.charbon2028]

What a splendid video. The horse analogy is one for the books, clear and understandable. Thank you again Uncle Doug.

[@UncleDoug]

You are very welcome, RC.

[@MaBaKar]

As a very common man, I found this very helpful. Thanks Uncle Doug!

[@UncleDoug]

So glad you enjoyed it, Ma.

[@brianchambers1399]

Thank you so much for your very careful, human and witty explanations. Until I found your channel I was totally clueless about schematics and what happens under the hood … A friend has been helping me refurbish a !951 Fender 5A3 Deluxe which I bought at a hock shop for $50 in the early seventies, and which "died" a couple of years later. Luckily I hung onto it, and what a sweet amp it has turned out to be! I think what I like most about your videos is your patient and non-condescending attitude to the total neophyte-keep up the good work …

[@UncleDoug]

You're quite welcome, Brian. It's great to hear that the videos are helpful and I really appreciate your kind appraisal. People who talk down to their audience are generally more focused on ego than education. Good luck with your amp.....it sounds like a real gem :)

[@DetroitWrecker666]

Uncle Doug, as you know, the past few days, I have been taking a crash course with your videos. I am learning SO MUCH!!! And using the Schematic for my amplifier, to follow along. Everything is becoming clearer! Thank you!

[@UncleDoug]

That's great to hear DW. Best of luck with your continued education.

[@frankymcdonald3081]

I tune in because i know "your not making this up." Thanks for another piece of the puzzle. Your a good man, keep it up.

[@UncleDoug]

Thanks, Franky. I like to apply the theory to real, "live" circuits....so people can start to interpret schematics on their own. That's why I included the resistor information in the video. All the components in a circuit are there for a reason, and it's nice (and important) to be able to figure out what that reason is :))

[@richclayton5785]

I was referred to you and this vid by a bunch of great folks at the Marshall Amp Forum. Thanks for making muddy waters clear for me.

[@UncleDoug]

You're welcome, Rich. Glad the video was helpful.

[@HHTTRRNN]

I really appreciate this common sense explanation of a process that easily escapes understanding. Excellent presentation! Many thanks.

[@ΚΩΣΤΑΣΠΑΝΑΓΙΩΤΟΥ-κ7ξ]

Dear uncle Doug. I discovered your films last week and I must confess that I became a Dougoholist. I play guitar and I am thinking of building my first amplifier. Congratulations for your detailed films which are very helpful. Also congratulations for your love for the animals which tells a lot for your character

[@UncleDoug]

Thanks for your nice comments. We're glad the videos are helpful, and wish you the best with your project.

[@joeseefeldt8192]

Wow. Simply the simplest and most understandable explanation of phase inversion I have encountered. Thanks Doug. I know so much more now!

[@UncleDoug]

Thanks, Joe. That's our goal :)

[@RadioWerwolf]

Could'nt be explained more efficient and simpler. The two horses analogy was awesome. Thank you Uncle.

[@UncleDoug]

You're welcome, LS.

[@stevenkimsey7039]

I find this fascinating. It's an older lecture, I understand. Professor Doug is always worth a curious person taking a look at older videos/lectures. Thank you Doug for sharing 👍🍺

[@UncleDoug]

The pleasure is ours, Steven. Thanks !!

[@themarcoharder]

Finally, an explanation of phase inverter principles that I can understand, particularly the LTPI section. You really have the mark of a great educator, Uncle Doug. Thanks!

[@UncleDoug]

+themarcoharder You're welcome, Marco.....glad it was helpful :)

[@scuzz152]

Many, many thanks for all your videos. As a completely self taught "tube jockey" I have learned more from your videos than the dozen or so Tube Amp books I have read. I had been making some beer money by repairing amps and guitars for guys in my band and other local musicians and now after watching most of your clips, I am much more confident and inspired. Including Rusty and Jack is also a very nice touch. Thanks again! Scott

[@UncleDoug]

+scuzz152 You're quite welcome, Scuzz. It's great to hear that the videos have helped you to help others. Best of luck with your new tech career. It's the same way Rusty and I started out, and I tend to think that self-teaching, using Internet resources, is the best way to learn. Best of luck from R & UD.

[@scottsagor674]

another SPOT ON vid - than you so much for explaining this and adding the context of the engineering decisions (and considerations) around those designs at the time.

[@UncleDoug]

Thanks, Scott. I'm glad you enjoyed the video :)

[@petermayonejr.3420]

Excellent, captivating, educational, substantive, information on all the intricate operational features of tube amps; The BEST on the web! TY.

[@UncleDoug]

Wow.....thanks so much, Peter :) Please see all our other videos. They provide a gradually increasing level of complexity to the basic foundation laid in this video.

[@sin1949]

Thank you Uncle Doug this World needs more amassing people like you.

[@UncleDoug]

You're welcome, SP, and thanks for your very nice comment :)

[@kenjimac2211]

Thank you for that UD. A dear friend of mine used to try to explain this exact same thing to me before he passed away (RIP my old friend Mike). I had trouble with his explanation at that time but makes perfect sense to me now. Mike would have really enjoyed watching your videos, I know I do.

[@UncleDoug]

You're welcome, William. I'm sorry for the passing of your friend, but am glad you enjoy the videos.

[@andrewfaile3537]

This is a great video - I’m an EE and Doug’s explanations are spot on and at a good level for those that desire an “uncluttered” understanding of these principles. I really appreciate his patient manner in explaining what can be very complex concepts - his ability to distill this down to the essence and calibrate it for use by a person in the DIY field is wonderful. Great job Doug!!

[@UncleDoug]

Wow....thanks so much, Andrew. It's great to hear that our videos are effective.

[@michaelogden5958]

Man, wrapping my head around signal and B+ voltage playing in the same sandbox trips me up every time. But I'm learning, thanks to you!

[@UncleDoug]

That's good news, Michael. Keep it up :)

[@rickcarter6591]

Wow, just wow. I think this is the first time I have not drifted off to “Liberty call” while learning about phase inversion. It has cleared up so many questions for me. Congratulations on 100k subscribers. I am a recent subscriber and have been loosing a couple decades of rust in my grey matter before I restore a stock ‘65 Falcon I recently acquired. I truly appreciate your videos, especially your instructional vids. No frills, just the needed information. wish I paid more attention in algebra class.

[@UncleDoug]

Thanks so much for all your nice comments, Rick. Good luck with the Falcon project......I love that body style.

[@1inDnile]

Well thank you again Uncle Doug this is probable the most important piece of info i have ever received on my journey to understanding Valve amps, I wish that you could have told me this in 1955 when I first took apart and tried to mend an old Radio that we had lying around the home in Leicester England when I was just 6 yrs old it's a light bulb moment for me for sure 1000 watts of brightness,Thanks again I'm sure many young and old alike will benefit from your wisdom,I love the analogy of the horses,keep it up Dougie.I like your hot rods but much prefer you electronics.

[@UncleDoug]

You're welcome, David. It's great to hear that the videos are helpful :)

[@edwardkujawa]

he is a great technicial love him God Bless him wish he was around back 25 yrs he would make it soooooooooooo easy kudos to him

[@UncleDoug]

Thanks, Ed. I was around 25 years ago......also 50 years ago.......and 75 years ago......

[@MC-bu6ez]

Thank you for such a great explanation of phase inversion, a subject quite complex for non specialists to follow, great tutorial.

[@UncleDoug]

Glad it was helpful, Mario :)

[@romannumeral5547]

Thank You very much Doug for a straight forward explanation of how phase inversion works and why it's used. It's really nice to not have a bunch technical jargon to have to decipher. Love the horse analogy. 🤗

[@UncleDoug]

You're welcome, RN.....Glad you enjoyed it :)

[@user-mk5mt3fg8m]

Thank you for a truly understandable explanation of why and how phase invertion is used and how to achieve this result.

[@UncleDoug]

You're welcome :)

[@michaelmiller-ce4du]

Doug, you are the most informative teacher on YT. Some can relay information but the best teach in a way that gives understanding on the listeners part. You're one of the best and much appreciated. I have spent hours pouring over Fender circuits. Now I understand how they work. Thanks! You're awesome!

[@UncleDoug]

+michael miller You're welcome, Michael, and thanks for the very nice comments. Rusty and I sincerely appreciate them.

[@nicky5185]

The horse analogy is brilliant. It made me understand the concept perfectly. Perhaps that is what makes your videos different and more attractive than those others who adopt a more academically correct approach.

[@UncleDoug]

Thanks, Nicholas. I'm glad the use of analogies helps to clarify the more abstract principles.

[@George.Andrews.]

Thanks Doug . Very easy to keep up with you . I know more now than a little while ago. Mission accomplished.

[@UncleDoug]

You're welcome, George. That's our goal :)

[@jonstepheno]

I've been a musician my whole life and despite my best efforts never really understood how amplifier circuits worked. It seemed like electronics was some kind of secret magic shared by a select group of privileged people who spoke a different language. Vacuum tube books and amplifier repair videos made a lot of sense if you already knew what they were talking about. I learned more this afternoon than I ever thought possible......I get it. Thank you! I've got a room full of old amps that I can't wait to tear into. Kudos.........and please keep on posting these great videos.

[@UncleDoug]

You're welcome, Jon. I'm glad to hear that the video was clear and helpful. I have posted almost 100 videos so far, and quite a few are technical presentations that you might find interesting. Thanks for watching and for posting such a nice comment :)

[@mushtaqobaray7529]

Wonderful. More clarification. Clearer explanations on the art of electronics. Good clear diagrams. Satisfies the hungry.

[@UncleDoug]

That's good to hear, MO.

[@jsullivan2112]

Brilliant! The horse analogy finally made everything click. Thank you!

[@UncleDoug]

You're welcome, JS. Glad it was helpful :)

[@williamgregory6684]

It is good to be learning something new at age 66,espeically? something I have been interested in probably since birth.You explain things in a basic way that's easy to understand.I wish you had been my Algebra teacher! I probably need to brush up on my spelling too.Thanks so much for sharing your incredible knowledge with us!!

[@UncleDoug]

Thanks for your very nice comments, William. My feeling is that we should never cease to learn.....never surrender to complacency :)

[@utapandgo]

Flip me daisy - that was so awesome learning - I pulled my amp out and want to start fixing it myself. thank you so much.

[@UncleDoug]

Glad to hear it, U......be careful !!

[@nickvictor7398]

Thank you uncle Doug for all of your information and teaching ability. I have learned much from you.

[@UncleDoug]

You're welcome, Nick

[@sixstringmarauder]

Once again ,splendid job uncle Doug, I love the visualization you bring with things like the horses pulling in the same direction, being a mechanic for the past 30years it helps when I can visualize the inner workings of these systems.

[@UncleDoug]

Thanks, David. I think that providing "mental pictures" of abstract events really does make them easier to understand. Like you, I've been a mechanic most of my life and this approach just seems like a natural progression.

[@kasepe]

Well.done,..simple.and..straight.forward...If.someone.does.not.get.push.pull.operation ..with.your.tutorial...he.is.doomed.

[@UncleDoug]

Carlos Serrano Thanks, Carlos.....glad you liked it :)

[@qua7771]

I finally understand my amp's output section (Bad Cat Cougar 50 with a long tail pair). It has been 30 years since my Navy electronics class and I couldn't figure out where the second tube was getting it's input. It appeared to me that the cathodes tied together were simply a shared grounding point, and the output was a rabbit being pulled from a hat somehow. Now I see. Mine has the same resistors and caps on the output of each tube. I assume that is to retrain an unbalanced PI for more second order harmonics. Nice. I cannot count how many forums I have read where people think they need a balanced tube for this position. Thanks again for creating a very useful tutorial.

[@UncleDoug]

You're quite welcome, AR. I'm glad the videos are helpful.

[@dnbibbo2248]

Makes sense now I see that the LTP looks like a differential amp.

[@silasfatchett7380]

@@dnbibbo2248 It IS a differential amp.

[@arthurvandelay7677]

Another great video! Just a note...on the 135 watt Twin Reverb, the plate resistors for the phase inverter are of the same value. Balance is achieved by adjusting the "Output Tubes Matching" pot on the back panel. Turn the master volume to zero, and if you still hear a little hum from the speakers, trim the pot until the hum disappears. Now the inputs to the output tubes are balanced. If you've removed the master, just use the remaining volume controls. I'm not sure why they did this, but I'm sure they had a good reason.

[@UncleDoug]

Thanks for the helpful tip, Art.

[@abeleballestri612]

Thanks very much for the detailed explanations of how an output stage works preceded by an amplifier in push-pull system working together.

[@UncleDoug]

You're welcome, Abele. We're glad the video was helpful.

[@tonyhills2112]

As usual, Doug’s tutorials ring clear as a bell. Superb!

[@UncleDoug]

Thanks so much, Tony :)

[@Rodedog55]

Thanks Uncle Doug ! I Love your Videos and Teachings here ! Keep Preachin' and Keep Teachin' !!! Your videos are valued highly !

[@UncleDoug]

Thanks so much, RD.

[@germona]

As a horse owner, i can confirm that if the driver does not give the same signal to both horses no work will be done.....:=) Very informative Sir Thank You.

[@UncleDoug]

Thanks for confirmation of my analogy, Jean :)

[@rolandmengedoth2191]

Very good explaination of the basic functionality of these curicuts. Easy explained, easy to understand whats going on. From the engeneers perpective there are of course much more details, but for this topic and for most electronic "amateurs" its fair enough. Thanks great Video.

[@UncleDoug]

Thanks so much, Roland. We have posted additional videos of greater sophistication for those who desire more information.

[@stefancallaghan5513]

Really great video, answered all of my questions. I am no longer confused and it feels great.

[@UncleDoug]

That's great to hear, Stefan.

[@sachmostaub1990]

Beautifully explained. I enjoyed every minute. Never had any idea of how tubes functioned. Thanks

[@UncleDoug]

You're quite welcome, Anne Marie :)

[@Furax02]

Uncle Doug - first, I'm incredibly grateful for these videos - I can't believe it took me forever to find them. Second, the horse analogy is brilliant. Thank you for doing everything you do!

[@UncleDoug]

You're welcome, F. It's great to hear that our videos are helpful :)

[@scuzpwns3934]

I'm late to the party but please do more of this. This was so good I feel like I have a handle on it even as a complete beginner. Thank you for taking the time.

[@UncleDoug]

Will do, S. You're welcome.

[@Shadowcruise99]

Just ran across this particular video, Doug. I think you did a phenomenal job of explaining practical phase inversion. Thanks so much for posting this!

[@UncleDoug]

Glad you enjoyed it, SC.