Four Different Types of Power Supply, Part 1: RMS, Diodes, Half-Wave Rectification

This is the first video in a series that will explain the function and differences between four different types of power supply: 1.) The Half-Wave (commonly used for tube bias negative DC voltage) 2.) The Full-Wave (most common of all tube amp power supplies 3.) The Full-Wave Bridge (very efficient, it utilizes a less-expensive power transformer than FW) 4.) The Voltage Doubler.....and how it can be used to build very economic tube effects, like a boost and tremolo unit, or even a simple low power amplifier. For many of you, this will be your first experience with this very interesting and useful circuit.
NOTE: Please be sure to watch the companion video to this one. It features oscilloscope views of the half-wave rectification process and the smoothing effects of filter capacitors upon the highly rippled DC wave form. Link: • Oscilloscope Views of ...
The first few minutes of this video are dedicated to a review of RMS vs Peak Voltage measurements, and an explanation of Diodes and how they are marked and function. If you already know this or are not interested in a review, then prompts will be provided to allow you to skip over them.
Thanks for watching.

[@aubreywalker7172]

You are hands down the best teacher I've come across on electronics. Thank you for your contribution.

[@UncleDoug]

Thanks so much, Aubrey. Glad the videos are helpful.

[@scottschooling4354]

I am building a Harvard and planned to substitute a diode for the selenium rectifier in the bias supply circuit, but then began to second guess the decision. Your video very clearly explained the process and now I can proceed. Thanks once again for explaining electronics to me. Your a huge help always, and a gifted teacher.

[@UncleDoug]

Thanks so much, Scott. Good luck with your project.

[@m0dad]

This is without a doubt the best tutorial I`ve ever came across on power supplies. Very well explained and presented. Thanks for sharing and best wishes from North East England.

[@UncleDoug]

Wow....thanks, Dad. So glad you enjoyed it.

[@JCHaywire]

A couple years back I lost my grandpa at 98--a good long run. He was a test equipment calibration engineer for Collins Radio in Cedar Rapids, IA for 30-some years. As radio amateurs, we shared many interests despite a significant language barrier. My language was from audioland--small, solid state kit-built devices that fit in the palm of your hand. He laughed because he couldn't even SEE most of the components. Grandpa's language was point-to-point, high voltage, heat-producing, wooden chassis and wrinkle painted communications equipment. Stuff that you would need help lifting into the rear hatch of your AMC Pacer. Your videos are the bridge between his world (the physical remnants of which now fill my basement workshop to bursting) and mine. You seem to be responding specifically to my requests, and whether or not that is the case, I couldn't be more pleased. These fundamentals, sometimes repeated, are EXACTLY what I need to get further enjoyment from this subject matter. If the higher voltages don't kill me, that is. So, that's my rather long-winded thanks.

[@UncleDoug]

+JC Haywire JC, thanks for the input....not long-winded at all.....Rusty and I enjoy hearing from you and appreciate your observations and comments. Your grandpa sounds like a great guy. My own grandpa was a master machinist and line supervisor at L.S. Starrett Co. so, like you, I have a nice assortment of precision machine tools and a snazzy brass & cherrywood cabinet (custom made in the Starrett cabinet shop) to keep them in. When I croak, I have no idea what will happen to all my "treasures". My immediate family has no real interest in any of it......so keep an eye out for the big estate sale that will immediately follow my demise :)

[@Taronlusin]

I want to double all "Thank you" from 217 comments and make it 434 time thank you. I enjoy watching these videos.

[@UncleDoug]

Thanks, Taron. We're glad to hear it :)

[@murratosmani6517]

Great video! Desperately waiting for the next episode. Thank's for the time you spend for us!

[@UncleDoug]

+Murrat Osmani You're welcome, Murrat. Thanks for watching :)

[@damianvila]

You're my hero, Uncle Doug! It couldn't be clearer. Thanks!

[@UncleDoug]

+Damián Vila Thanks, Damian :)

[@stephendaniels6569]

Uncle Doug, your videos are both educational and entertaining. I've been quietly enjoying the fruits of your labor for a couple of years now and it seems only fair to let you know how much I appreciate it. This new series is timely and I look forward to the rest of it. Give my best to Jack and Rusty.

[@UncleDoug]

+Stephen Daniels Greetings, Stephen, and thanks for your very nice comments. Rusty, Jack, and I really appreciate the time you spend watching our videos :)

[@mixolydian2010]

Thanks for the video you a have been very busy, i was wondering why you hadn't posted a video for a while, guessed you where out in the desert driving around, but you had been very busy making a whole load of videos to educate and entertain us with. Thank you for taking the time to do this i always learn something from your videos and love the way you present them. Take care and hi to Rusty and Jack. Colin

[@UncleDoug]

+mixolydian2010 Thanks so much, Colin. It's always great to hear from you....and, yes, we were out riding around in the desert, but always thinking of new video topics :)

[@DavidWilliams-fx9pw]

Excellent videos. I'm starting my first scratch-built amp using your techniques and I don't even play guitar. One minor nit, every time you pause, your record switch inserts an audible scratch to your soundtracks. You can edit these out or oil you switch. Or not - I'll still watch.

[@UncleDoug]

+David Williams Thanks, David. I tend to shoot and re-shoot lots of short scenes and then edit, select, and combine them into a video. The sound is indeed me hitting the record switch. Editing it out would take hours of time, so I guess it's just an unavoidable, but hopefully tolerable, annoyance.

[@SiliconSet]

Many thanks for the video Doug! It's always a hoot having Jack and Rusty's involvement.

[@UncleDoug]

You're welcome, SS.....glad you enjoy the pet cameos.

[@thelonious-dx9vi]

Another masterly ... master class, Uncle Doug. Thanks and best wishes. I'm signed up over at Patreon, and it's the smartest spend in my whole budget ... if that's the right word for it.

[@UncleDoug]

Thanks so much, T, and thank you for your support of our channel.

[@johncunningham5435]

Very nice demonstration; including the Voltage Doubler, I use to work with those with very interesting results.

[@UncleDoug]

+John Cunningham Thanks, John. The Voltage Doubler will be covered in Part 4, which I am currently working on.

[@budandbean1]

Hi Uncle Doug, one of my favorite "black arts" of electronics... Rectification. I totally understand it now but my instructor back in the early 70‘s made it seem more of a bit of magic. You are a great teacher, thank you for all your videos. Also liked the scope video, (black magic) Ha! Buddy

[@UncleDoug]

+Buddy Martin You're welcome, Buddy. We're glad the video was helpful :)

[@ImTheReal]

Great!!! Is pretty easy to understand. Thanks for sharing your experience master✌

[@UncleDoug]

+Humberto Martins Ferreira Junior You're welcome, Humberto :)

[@MrHeggeb]

These videos are the best. Thank you

[@UncleDoug]

+Brian Hegge You're welcome, Brian :)

[@elluisito000]

Hello! :D some years ago I read a book that said that when it comes to well-madeaudio amplification and processing, what you really hear is the quality power supply, and I also read a blog that said that a good power supply is like water to beer, you have to have good quality water in order to have good beer :D Thanks again for sharing your knowledge Uncle Doug

[@UncleDoug]

+luis colmenares You're welcome, Luis. That's an interesting observation and I agree with it completely. The power supply is like the foundation of a house....if it's not rock solid, then no matter how good the quality of the structure, it will eventually fail.

[@daleburrell6273]

...and that's perfectly true-!!!

[@cawfeedawg]

I always learn so much from your vids Doug. Thank You... looking forward to the rest of this series.

[@UncleDoug]

+Cawfee Dawg Thanks, CD. It can be a rather demanding topic, but it's one of the most important and least understood parts of any amplifier circuit.

[@EUC_Senior]

I work on switching power supplies for a living and I will be installing one into one of my amplifiers soon.

[@UncleDoug]

Sounds great! Good luck.

[@td7456]

Good series, looking forward to part two! Seems like, if I recall correctly, back in the day, after using some strange leafy vegetation that I, like Jack, really didn't want to fetch much of anything either.......

[@UncleDoug]

+Tim Dockery Thanks, Tim. No kidding about the negative effect of burning leaves on work ethic.....occasionally it was difficult to even get up off the floor :)

[@PrinceOfBodom]

I am happily supriced about this series and can't wait to see whats possible if we use two or four diodes. Also i am very excited about the voltage doubler. I just ordered parts for a flanger using 18V and it would be really handy to use a 9V supply like most other pedals do.

[@UncleDoug]

+PrinceOfBodom I'm glad you're excited, PoB, and hope the videos answer all your questions. The voltage doubler requires AC, not DC like a 9V battery, but you could always use two 9V batteries in series.

[@thierryhanot7610]

Hello Sir, thank you so much for your videos always so clear and easy to understand. My deepest regards to you, Rusty and Jack ! Please keep on sharing your passion. Thierry

[@UncleDoug]

+thierry hanot You're welcome, Thierry. We appreciate your kind regards and wish you the best :)

[@psu2xj]

Hi Uncle Doug! A suggestion for another video: Input and output impedance of a stage. How to calculate it, how the I/O impedance of one stage affects or influences the next stage, and what the authors of the amp books mean, exactly, when they say "the impedance that's 'seen' when looking back into a stage". I don't know why this is so confusing to me, but it is. Thanks and keep up the great, amazing, teaching!

[@UncleDoug]

+Sam Owens You're welcome, Sam. The statement is a little confusing to me too, so don't feel bad. I'll keep your suggestion in mind and do some research.

[@billguitarvin]

+1 on a video about impedance in the different parts of a tube amp.

[@PhuketMyMac]

congratulations on the 100k subscribers uncle Doug!

[@UncleDoug]

Thanks, PM :)

[@unicorneggspam]

I really enjoy your videos. Excellent explanations. I know you said you're in central Texas. I recently moved away from Brownwood. I really regret not stocking up on cheap tube projects in the thrift/antiques stores out there!

[@UncleDoug]

+unicorneggspam Rusty and I are actually in West Texas, Uni. Thanks for your nice comments.

[@wtangodelta1715]

Wow, that did not take long! The catnip not only made for a mercifully short educational 'trip', but I found the presentation to be Most Tolerable as well:) P.S. Thanks for putting up with me~I know it's not always easy...but apparently it's necessary. I don't know why either!

[@UncleDoug]

You're welcome, WTD :)

[@francismannion7075]

Fantastic video , I think it was very well done and fun to watch too. Thank you .

[@UncleDoug]

Thanks, Francis. We have many, many more similar videos for you to watch. You're welcome.

[@audiotechlabs4650]

Hey, here we go again! EXCELLENT. Great new series and am biting my nails for #2. Thankz

[@UncleDoug]

+Audio Tech Labs You're welcome, ATL. I am in the process of uploading a companion video in which I use an oscilloscope to demonstrate half-wave rectification and how the ripple is smoothed by a filter cap. I hope you enjoy it too.

[@audiotechlabs4650]

+Uncle Doug That's a great idea! Not only explain it on paper, but show it on a scope! Thankz

[@UncleDoug]

You're welcome, ATL. The oscilloscope video is posted and ready to watch.

[@Earlvis]

Hi Doug-The bias tap from the transformer feeds the grids with negative voltage which I understand. I presume there is no current flowing in this circuit, correct? Thanks for all you do for the amplifier community. You have changed many lives for the better!

[@UncleDoug]

A tiny bit of current may be generated by the capture or loss of electrons by the grid, but it is negligible. We are concerned only with the net charge upon the grid and its effect on current flow from cathode to plate. Thanks for your kind words :)

[@tectalabyss]

Fantastic to see a new series, Doug. Jack is truly like Molly :) even to the way they curl their tails and the laying down on the job Lol. Your videos has always something I very much look forward too. Give Rusty and Jack a pat and scratch for me. All my best. Bobby

[@UncleDoug]

+Bobby Tectalabyss Thanks, Bobby. Rusty and Jack send their regards :)

[@crabejoss]

Another great serie ! Thanks for your work !

[@UncleDoug]

+Josselin Soteras-Condé You're welcome, Josselin :)

[@killarmy220]

Very basic, good for young players ! Thank you sir.

[@UncleDoug]

+killarmy220 You're welcome, KA....glad you liked it :)

[@AndyWragg]

Great work once again Uncle Doug.

[@UncleDoug]

+Andy Wragg Thanks, Andy :)

[@davidportch8837]

Thanks Doug for another good video. I was just asking myself at one point of this video... if the mains voltage is peak to peak, why does it measure 240 volts (here in the UK) when - as if by magic - you then went on to explain how the voltmeter automatically reads the rms voltage on the AC range! So I learnt something new again... :-)

[@UncleDoug]

You're welcome, David. I'm glad the video was able to answer your questions.

[@alexanderross2786]

Realy great!! Filled a few gaps!!

[@UncleDoug]

+Alexander Ross Just like the filter caps :) Glad you liked it.

[@Bleats_Sinodai]

There's an amp project from the tube amp section off the Brazilian forum Handmades, where they use a 30v+30v power transformer with a doubler to get 150v B+ for a parallel-single-ended amp with 2x PCL82, giving about 6w of power output. The way they did it was connecting one of the 30v wires to ground, a half-wave doubler connected to the other 30v wire, and then they tie the tubes' filaments in series to power them from 30vAC. The pentodes are connected in parallel for the output stage, and the triode make 2 gain stages. They proposed something akin to AX84's P1, but I'm currently looking to build it based off the Supro Super 1606 amp.

[@UncleDoug]

Thanks for sharing, BC. That sounds like an interesting project.

[@tubical71]

Very good, as always, Doug!

[@UncleDoug]

+TubiCal Thanks, TC. I am in the process of uploading a companion video in which I use an oscilloscope to demonstrate half-wave rectification and how the ripple is smoothed by a filter cap. Although this is old news to you, I think it will be helpful to many.

[@michaelmasin1996]

Love the content you do, really, your videos are ones of the most instructive on the whole "youtubeland"

[@UncleDoug]

+Michael Masin Thanks so much, Michael. Rusty and I really try to make concepts as clear as possible, and comments like yours are very reassuring.

[@MarkPilipczuk]

Nice work as always Doug! You're making things very easy to understand for me. I appreciate the effort and time you put into making these videos! P.S.--as a cat guy, more Jack!

[@UncleDoug]

+Mark Pilipczuk Thanks, Mark. Jack, Rusty, and I appreciate it :)

[@cassvirgillo3395]

Hey Uncle Doug & Rusty, I never fail to learn something from your most excellent videos. I know RMS is Root Mean Square, I believe its the point midway between the peak and valley of the sine wave, be it positive or negative, correct me if I'm wrong, and I could be. When I build a power supply, I always use the full wave bridge, and smoothing caps. Still learning so I really appreciate your great hand drawn graphics and insightful explanations of the process. I think it was just Teacher appreciation day and I really do appreciate your teaching and sharing of your knowledge and experience, Thankyou. You and yours take care & be good, C.

[@UncleDoug]

+Cass Virgillo You're welcome, Cass. As Wikipedia says, "For a cyclically alternating electric current, RMS is equal to the value of the direct current that would produce the same power dissipation in a resistive load". It's not the midway (0.5 out of 1.0) point......it is the .707 point. Thanks for your very nice comments. Our best to you.

[@utubehound69]

Old Black Jack Haha. Enjoyed the upload as always, Thanks Uncle Doug!

[@UncleDoug]

+Watchman4u You're welcome, W4 :)

[@StonyRC]

Uncle Doug, have you ever written all this "stuff" down? Your educational musings would constitute the finest reference source on electronics and valve amp technologies. Others have tried, but they are pretty inaccessible as they miss out on the underlying theory that you must have to understand how it all fits together. Sir, you are a natural and gifted Professor.

[@UncleDoug]

+StonyRC Wow, Stony, thanks so much. No, although I do have files containing my notes and diagrams for each video, I have never written everything down. I guess I consider the YT videos to be a verbal transcript.....sort of an Internet "book"......of theory, practice, projects, etc.

[@kwsailer1]

Great presentation! Thank you for sharing!

[@UncleDoug]

+kwsailer1 You're welcome, KW :)

[@bullthrush]

Pop quiz 262V. In Jacks first clip he looks like he's saying " man, your drying my oils" :)) Rusty says bone first, then we'll negotiate a work deal. Looking forward to the rest of the series.

[@UncleDoug]

+bullthrush You get one more try, Andrew. Recall that the peak voltage is always higher than the RMS and in this case is measured across the entire secondary. Thanks for watching and commenting :)

[@bullthrush]

+Uncle Doug After studying a few videos from my favorite tube amp channel, my second answer is 524vpp. If I'm still wrong, I'll stamp my own meal card "No Dessert". :))

[@UncleDoug]

If the two secondaries are 325VAC RMS each, then the pair would total 650VAC RMS. This value times 1.414 would yield a total peak voltage for the secondary of _______ .

[@bullthrush]

+Uncle Doug 919V pp, I'll do some more reviewing.

[@bullthrush]

+bullthrush I've found my mistake..... I wrote down the turns ratio as 1.54 :1

[@TheGuitologist]

An interesting side note to the .707 figure when calculating RMS from peak voltage, I believe this is why when you bias output tubes in push-pull, you use the 70% of max plate dissipation rule.

[@TheGuitologist]

+The Guitologist another great series I've already learned from. I'd totally forgotten (if I ever knew) the 120VAC from wall was RMS.

[@UncleDoug]

+The Guitologist Thanks :) I caught some flak on my first power supply video (several years ago) when I forgot to include RMS, so I made sure it was emphasized in this series. To me, it's actually rather abstract, since at no time is peak voltage ever physically converted into RMS, it's simply a theoretical/mathematical way to equalize their respective energy contents. However, since voltmeters report values in RMS and oscilloscopes deal in peak voltage, you have to be aware of the difference, or strange problems will arise when you try to use both instruments in tandem. I always thought the 70% value for fixed bias tubes was rather arbitrary, a simple rule of thumb, and allowed room for the average expected increase in plate current that accompanies high input, high volume use.

[@handwoundpickups6555]

Brilliant again thanks 👍

[@UncleDoug]

It was our pleasure, HWP.

[@seanhornibrook]

I just wanted to thank you once again for your excellent videos. Really great work you're doing here. Also - my cat will fetch but ONLY when she feels like it and ONLY when no one is watching - not even I. LOL Cats...

[@UncleDoug]

+SYNTHS!! You're welcome, Synths. Yes, indeed, cats are quite obstinate. Like yours, Jack will only perform when no strangers or cameras are around. Thus our claims of his brilliance often go unheeded :)

[@daleburrell6273]

Cats are very independent creatures.

[@tobiasgertz7800]

Any identical signal that appears on the grids of a pp output stage will cancel out. Just like in your analogy of the horses pulling in opposite directions. CMRR is usually something that applies to only differential pairs, but it applies in it's own way here as well. You are right about the ripple voltage being close to or under the noise floor of most output stages.

[@UncleDoug]

Quite so, Tobias, which is why push-pull circuits have less hum, since it tends to self-cancel in the output stage.

[@billguitarvin]

Hi Uncle Doug, and once again, thanks for all the incredibly informative videos you have posted over the last few years. One basic thing that keeps tripping me up is the AC positive waveform vs. the AC negative waveform. My understanding is the AC current is continually reversing direction back and forth, so when the current goes one direction it is a positive waveform and when the current reverses direction it is a negative waveform. If that is correct, does the positive AC waveform actually have a positive charge or lack of electrons when compared to the negative waveform?

[@UncleDoug]

You can look at it that way if you wish. The negative wave form reflects the number of electrons flowing, from 0 at first to the peak and then back to zero. The positive wave form reflects the departure of the electrons, beginning with 0 to the peak and back to zero. The overall "peak" voltage is measured from the height of the positive peak to the trough of the negative peak.

[@bertuspa3grn]

good morning as always a pretty understandable video Bertus

[@UncleDoug]

+Bertus pa3grn Thanks, Bertus. I like the use of the work "pretty" understandable :)

[@LanceHall]

Gotta skip through 16 minutes of electronics something something just to see that adorable black kitty. :-)

[@UncleDoug]

Jack agrees that his appearance is the best part of the video, Lance :)

[@umajunkcollector]

umathunkin a car transmission with drive and reverse to control direction for some reason, hmmm. Well done Dougski! Don

[@UncleDoug]

+umajunkcollector Thanks, Don :)

[@otteronbass]

thanks Doug.

[@UncleDoug]

+otteronbass You're welcome, Otter :)

[@saturn5tony]

Great review of Rms Doug! Too bad Jacks getting those lazy issues from Rusty. hehe. Thx4sharing.

[@UncleDoug]

+saturn5tony You're welcome, Tony, and thanks for the nice comments :)

[@mosestewelde8163]

Hi Uncle Doug, I just wanted to say I love you! I might as well drop out of college and learn from you, but I need that paper.

[@UncleDoug]

Thanks, Mussie, Rusty and I are flattered, but agree that a college degree should be your first priority.

[@thomasmiller5057]

I really enjoy the videos especially the jokey pet interactions. My question on this video is in the first example where the ac is rectified and half of the wave is clipped off... do the clipped off parts automatically push together like your drawing so that the clipped off tops of the dc “waves” only have to fill in the smaller ripples instead of the larger gaps that you mentioned later? Also further on you talk about the transformer taking in 120 VAC after you said wall current is actually 170 VAC until it is rectified. Maybe I missed something. Thank you so much for the videos

[@UncleDoug]

The filter caps don't "clip" the tops of the waves.....they absorb them.....then they discharge to fill in the valleys. I say 120VAC only because people are accustomed to hearing the RMS value. If I said that peak wall voltage is 170VAC, which it is, most people would not recognize the value.

[@petedazer2556]

Good job!

[@UncleDoug]

+Pete Dazer Thanks, Pete :)

[@daveogarf]

LOL! Jack is such a FELINE! :-D

[@UncleDoug]

Amen, Dave. He is 100% tomcat :>)

[@noreaction1]

Hi uncle Doug, could you make a video series explaining all about amperes, power, power variance and current flow? I am beginning to understand the use of voltage in an amp circuit, and would bet if you explained how current flows and how power changes in different stages of the circuit id just about have everything I want for Christmas.

[@UncleDoug]

I have already done so. Watch all of my videos and I believe your Christmas wishes will be answered.

[@lelandclayton5462]

Thanks for sharing this. I had no idea if you put a diode in backwards i will produce negative voltage.

[@UncleDoug]

+Leland Clayton You're welcome, Leland. Diodes are like selective gate keepers that only allow + or - current to pass, depending on the way they are oriented in the circuit.

[@lelandclayton5462]

I had always thought it would block the current or at lest most of it when a diode is backwards like with DC. Can't wait to see what you got in store next. Maybe a better way to do a charge pump / voltage doubler.

[@UncleDoug]

With DC, the diode will block any current that is of the wrong polarity. With AC, it only blocks half. Stay tuned.....good things are on the way :)

[@moodyga40]

yup can't wait got the popcorn

[@UncleDoug]

+ian “valve doctor” forster Neither can Rusty :)

[@brucewailes7744]

Thank you Doug. I'm currently dumber than a rock, but thanks to you, I am slowly getting a little better.

[@UncleDoug]

You're welcome, Bruce :)

[@CoolDudeClem]

Shouldn't the rectified and smoothed DC voltage be 170 volts? Like you said, the mains AC peaks at 170 volts, so wouldn't it just hold the peak voltage? That's what I get when I build simple power supplies for my projects. (although it's 240 volt over here, so i get around 340)

[@UncleDoug]

+CoolDudeClem The winding ratio in a 240VAC power transformer compensates for the higher (than 120VAC) primary voltage, so the secondary output voltage is the same as from a non-compensating 120VAC transformer. AC can be measured in either peak or RMS values, but DC can only be measured in RMS (since there are no "peaks"). You can talk about peak AC all day, but when you decide to convert (rectify) it to DC (which is only expressed in RMS) you must change the peak AC value to RMS (i.e. x .707) to calculate an accurate DC value.....otherwise it's apples and oranges.

[@kardRatzinger]

+Uncle Doug I think the question was about the part of the explanation that starts at 4:36, where you talk about how a filter cap turns a rectified sine wave with 170V peak voltage into 120V constant voltage. This is not actually the case. The rectifier diode + filter cap form what essentially is a very crude peak detector, it will hold the peak voltage, so the resulting constant voltage will be 170V, not 120 (at the cost of increased current draw from the supply of AC power).

[@UncleDoug]

I understand your point, Kard; however I think it boils down to what is the clearest, simplest way to present a topic in a video aimed primarily at relative newcomers to electronics. As you say, "increased current draw" is required to compensate for the 30% difference between 170VAC peak input and RMS VDC output. Is it best to simply state the basic reality of the 30% peak-to-RMS difference (as I did) or to also delve into the increased complexity of "peak detectors" and increased current draw compensation. When I make these videos, I try to cover all the bases for all the audience (hopefully without saying anything that is patently incorrect) but also by editing the content to avoid the endless digressions that would be required to cover every single detail of every issue. I apologize if my editing made this presentation incomplete for you, but I hope you can understand the diversity of my audience and the compromises necessary to reach them all.

[@kardRatzinger]

+Uncle Doug Hello, thanks for the response. Current draw aside, the point is, constant voltage will have the value of the peak rectified (unfiltered) voltage, not RMS. This is very beautifully shown in your next video with the oscilloscope waveforms - the filter keeps voltage at the level of the peak of the unfiltered voltage (or at least tries to, with varying success). I think this is very important, because when you design an amp with, say, 300V of B+, you have to be aware when ordering the power transformer, that the secondary winding cannot be a 300VAC winding, as this would give 423V DC (or maybe slightly less under load, but not a lot), which is way too much. Best regards.

[@UncleDoug]

Thanks for your informed and helpful input, Kard. Rusty and I appreciate your time and interest.

[@hadireg]

❤👍

[@BartManNL]

Hello Uncle Doug, at about the 14 minute mark you explain that 200 Vac is being run through a resistor "of some kind" to reduce the voltage to about 100 Vac. Is there a simple way to determine what resistor is needed? The only way I know needs to have data about the current (to apply Ohm's law) or needs two resistors (between Vin and ground) to 'divide' the voltage. Maybe I am just too impatient and need to view the other parts? Thank you for explaining all this in a way even I can understand!

[@UncleDoug]

+Bart Prins You're right, Bart. The reason I didn't state a specific value for the resistor is that it would vary based on (as you said) the voltage being delivered and the current passing through it. My method to determine the value would be to install a 100 or 1000 ohm resistor, measure the voltage drop, calculate the current, calculate the exact resistance needed to achieve the proper voltage drop, install that value resistor.

[@julesl6910]

Dr. Doug, I plugged my multimeter into the wall and got 117 volts. Just for fun. Am I to understand that the power supply can reach the heights of 170 volts, but we're getting a steady 117? Something is missing here, I'm not understanding. Is this a capacitance in the supply like it can temporarily supply that 170 volts? This is completely turning my brain upside down as I have learned to trust my multimeter. Edit - I reached 8:10 in the video and heard your explanation. What gives man. So the multimeter calculates RMS instead of peak voltage.... Now I need to explore multimeters that don't lie.

[@UncleDoug]

Almost all meters read in RMS. You need an oscilloscope to see peak voltages.

[@johnnybloom5729]

Thanks for producing your excellent video series! And good luck with Rusty and Jack; my own cats are even less helpful.

[@UncleDoug]

+Johnny Bloom You're welcome, Johnny. It's hard to imagine ANY pets that are less helpful than mine :)

[@rcard-eh7qi]

I used to see voltage doublers in Tektronix 600 series monitors. The problem with voltage doublers is the capacitors in the circuit would always go bad. Is this common with all voltage doublers?

[@UncleDoug]

I haven't had any capacitor problems in my voltage doubler circuits. Perhaps the capacitor voltage ratings were too low in the Tektronix monitors.

[@liumander]

Hi Doug, I got a bit confused. When u talk about the 170VAC I can see in the drawing 170V positive and 170V negative, making a total difference of 340V. Then you transform it to 170VDC positive. But when you talk about the 120VAC RMS and you rectify it only 60VDC positive (or negative) pass through? Why not 120 as the previous example? 120VAC wouldn't be 120V and -120V equals 240V? Anyway you are always teaching what I want to learn the next every time. It's kinda creepy XD. Thank you very much for your clarity on the explanations. PS: I think Jack is picking up bad habits from Rusty cause if he acts like Rusty maybe he'll be able to get any of the food that Rusty is stealing from him at next time.

[@UncleDoug]

+Edu "Turupá" Sánchez What happens when you add +170 and -170, Ed? It's definitely not 340. Same with +120 and -120. AC is not measured peak to peak, but is the height of a single peak, either up or down, with the appropriate sign. When AC is rectified to DC, 170VAC (peak) becomes 120VDC RMS. Watch the video again and hopefully it will become clearer. I'm glad my choice of topics matches your interests. Thanks for watching.

[@liumander]

+Uncle Doug but when u talk about the diodes and the half wave rectification, why 120V RMS (which is 170V peak) becomes 60VDC instead of 120?

[@UncleDoug]

You make a good point, Edu. The reality of what is happening is actually much more complex than I have represented. When the irregular (quite rippled) DC output emerges from the diode, the peaks are indeed as tall as the input peak (as you say), but its RMS DC value is equal to the original AC peak voltage (170V) times 0.318 which is 54.06VDC RMS. This value is a little below 60VDC, but for the sake of brevity and ease of understanding, I simply say that it is 60VDC. I hope this makes sense.....and that you can see why I glossed over the details.

[@etbilu5031]

If the full wave bridge rectifier is much cheaper than the full wave, why some old fenders were made using the full wave reticifier like the Twins ? Is there some diference? thanks

[@UncleDoug]

Any diode rectifier is much cheaper than a tube rectifier, Marshall. The Twin Reverbs had diode rectifiers because no single tube rectifier could provide sufficient current for the circuit.

[@etbilu5031]

@@UncleDoug I was wondering, what´s the diference between the old Twin (340 0 340 full wave) and the modern twin (350 full wave bridge) ? Is there any sound or quality diference? I build an old AB763 twin with a PT 340 0 340 full wave rectifier using a 25AWG secondary wire(420mA) and 18AWG 120volts primary, with a 3.88 square inch core. O notice some hot temperature on the PT. thanks

[@DollySvengali]

Here's another dumb question. I found some parts, and want to make a thing. I want a preamp made of 2 12ax7, done similar to jcm 800, so: Preamp1 , Cold clipper, Preamp 2, cathode follower, output. I found an old rack-mount chassis in a junkheap for an old cable TV rf amp, with 9 pin sockets and a power transformer, fuse holder, etc. So the power transformer has a secondary for filaments at 6point something, and a high voltage secondary which is center tapped. The volts on the secondary is 235/117/235 if you get me. There's no rectifier secondary, so it will be diode. So I'm thinking rectified, I ought to have 331vdc before filtering. Should this be plenty to run the preamp of 2 12ax7's? It's a big beefy transformer, and there won't be any power amp to drive, so I'm hoping to use it. Full or half-wave? And, how would I go about choosing the values of the filter caps? thanks.sm

[@UncleDoug]

The PT sounds like overkill for 12AX7's. Always full-wave if possible. When in doubt install a 20uf and two 10's for filtration.

[@DollySvengali]

@@UncleDoug Thanks. I knew you'd know! Maybe there's enough power left over for some output tube if I wanted to drive an OT and speaker some day. It's just a tinkering testbed right now. thanks again!

[@munceyboyjoe]

Can I ask why is the voltage halved in half wave rectification and not in full wave rectification? After the diode stage in both, it appears as though the size of the waveform would be the same in both techniques, only that full wave allows you to combine two out of phase waveforms for less ripple?

[@UncleDoug]

Half-wave rectification is like a picket fence with every other slat missing. Full-wave is like a solid fence. Obviously the latter contains twice as much wood (voltage).

[@munceyboyjoe]

Thank you, so is it that when you eliminate the large ripple/gaps in a half wave rectified waveform say with a filter capacitor, you end up with a lower DC voltage than say, a filtered full wave rectified waveform? I'd just like to add that your videos are hands down the best and warmest sources of information I could hope for. If you were a teacher, school would have been great!

[@UncleDoug]

@@munceyboyjoe Actually the voltage is about the same, Sed, since the overall amplitude is not reduced in the half-wave form, but the ripple is much more pronounced and can be a bit noisy unless fully filtered.

[@Satchmoeddie]

I bought a BIG HUGE SCARY MONSTER power supply that was supposed to put out 0-600 Volts fully regulated between 0 and 1000 mA, but all I could get was 300 Volts. When I started chasing down problems I noticed my Fluke 87 was showing the WRONG AC voltages. All of the AC voltages shown on the schematic were PEAK voltages, not RMS. Some old schematics might show PEAK Volts, RMS Volts or even AVERAGE Volts for Voltages too. You really have to be ready for that with some of the old electronic schematics. RMS voltmeters were not very common at one time. When I saw 1200 instead of 1697, it became rather obvious that I was reading the RMS of 1697 volts peak. Then I got to the reference supply trans, and I should have seen 800 volts RMS or 1156 peak, but instead I got 480 volts RMS. Someone had blown up the 400-0-400 RMS transformer and installed a 240-0-240 in its place. That explains the 300 Volts that I was missing. I found a 578-400-0-400-578 volts transformer, added a 115 to 240 and a filament supply, and now it's running at its rated 0-600 Volts RMS and 0-1 Amps. If I swap to the 1156 taps, it will run up at 840 Volts @ about 600mA. The voltmeter didn't like it, but a resistor I added adds another 2x range to it. So now 420 Volts=840 Volts. I don't run it at 840 very often.

[@UncleDoug]

An interesting example of why we need to know the difference between peak and RMS voltages. Thanks for sharing this with us, Seth.

[@jjheaphy]

Good stuff! Jack needs more training though.

[@UncleDoug]

Thanks, John. He's young.....give him some time.

[@MrMac5150]

I wonder if a burglar could bribe Rusty with a few milk bones, he would probably get a hand shake on his way out.. lol

[@UncleDoug]

+MrMac5150 For half a cookie, he would probably lead them to where the gold doubloons are buried in the back yard.....and help to dig them up :)

[@ianhames2465]

Great video Uncle Doug, but .... Isn't it about time you credited Jack and Rusty,? I know those techies are responsible for the great audio/visual work. I'm guessing Jack is the mic boom operator and Rusty the camera operator as Jack is always lounging and stretching like most noise boys. Credit where credit's due. :-)

[@UncleDoug]

+semahnai Thanks, Ian. You're right.....Rusty and Jack are definitely the brains behind this little production company. They write the scripts, set up and operate the cameras and sound equipment, get all the legal clearances, do all the editing, etc. I just show up from time to time and mumble my lines, like a network news anchor :) :)

[@wtangodelta1715]

Maybe it's the catnip that I've been missing all these years...believe it or not I haven't tried it yet...Thanks for the Idea! I promise to let you know if it leads to any shocking revelations. Okay then...on with the show.

[@UncleDoug]

You're welcome :)

[@BrianMcNamara1]

Interesting that 170 V/1.414 = 120 V because 1.414 is also the number used to determine the length of the hypotenuse in a right-angled triangle. Is this just a coincidence?

[@UncleDoug]

The square root of 2 is one of the factors in the formula, DB. It doesn't have anything to do with the Pythagorean Theorem as far as I know.

[@eugenepohjola258]

Howdy. With all due respect. I feel obligated to comment your presentation. The filter capacitor does not clip off the peaks. Unloaded the rectifier will charge the capacitor to the peak value. However. If we use a choke large enough to uphold a constant current for filtering the load voltage will be close to the aritmethic mean value (not rms). The AC rms voltage does the same amount of work or energy that the equivalent DC voltage does. It is worth making sure to use a true rms meter when we want to measure the rms. True rms meters used to be called torque iron meters before. If we want to charge a battery the true rms of the current is not the value we should use to estimate charging time. We should use the arthmetic mean value. Arithmetic mean value meters used to called torque coil meters before. The true rms reading will be way larger than the arithmetic mean value. Finally. A cheap AC voltmeter is likely to be a torque coil meter (mean value). The needle scale is calibrated to show the rms, however. The correction coefficient is 1,11 times. Rms = 1,11 x mean. And please observe. This is valid for sinusoidal AC only. In high regards.

[@UncleDoug]

Thank you for your very detailed and helpful input, Eugene. We really appreciate it :)

[@eugenepohjola258]

@@UncleDoug Howdy again. Got inspired by your presentation. In my blog eugpoh40.blogspot.com I take the full wave power supply one level deeper. Some math is inevitable but should not be too difficult. I don't have the skills to make video presentations. My thinking gets convoluted when speaking. I have more success doing papers. Then I can use a pencil eraser ... Regards.

[@daleburrell6273]

5:10...that's only under a "no load" condition- when the amplifier circuit draws power, the ripple starts to re-appear.

[@UncleDoug]

Thanks for the info, Dale.

[@EUC_Senior]

Your cat reminds me of my dog. You throw something and she just looks at me with a smile and thinks, “I’m not getting that”

[@UncleDoug]

Jack actually does retrieve.....when he's in the mood :)

[@gioremi2161]

In 1998, a friend of mine came to me and ask if I could double the charging capacity of his tricycle....,a motorcycle with a sidecar used as a public transportation here in the Philippines....,without changing the coil of the magneto, the motorcycles at that time have only a 6 volt battery, he wanted to change the battery to 12 volts so he can install his car stereo. I used a voltage doubler ( multiplier) that I took from my television repair book, it's from the flyback section, using diodes and capacitors, I got more than a hundred volts so I removed a few diodes and capacitors and end up with a 17 volts DC which is just enough for charging a twelve volt battery....and it lasted for so many years.....

[@UncleDoug]

You are a true innovator, Sonny. Congratulations on a very clever and successful solution.

[@machinimafan27]

Uncle Doug, Is it a coincidence that 0.707 is the sine of 45 degrees in a unit circle?

[@UncleDoug]

To be honest, there may be some relationship, but to me, it's simply a matter of 0.707 being the reciprocal of 1.414, which is the square root of 2, and when the square root of 2 appears in the denominator of an equation, it's the same as multiplying by its reciprocal.

[@machinimafan27]

@@UncleDoug Thanks for the explanation. I remember just enough about trig and calc to be extremely dangerous lol. I think it's better or me to KISS!

[@UncleDoug]

@@machinimafan27 It's good that you remember it, MF. Most people don't :)

[@kevinwilkins9926]

Why are the power transformers used have so much output if we end up putting dropping resistors in to reduce it so much?

[@UncleDoug]

Almost all of the output of the power transformer is sent directly to the output tubes. In the remaining output, the voltages are lowered to suit the needs of the pre-amp tubes, which have lower voltage requirements.

[@kevinwilkins9926]

@@UncleDoug thank you for your quick and informative responses. Appreciate it.

[@UncleDoug]

You're welcome, Kevin.

[@tommyfoley]

My guess at the pop quiz: 170 PVAC X 5.4 winding ratio = 918 Peak Voltage AC.

[@UncleDoug]

+tommyfoley Yes, indeed, or you could multiply 325 x 2 x 1.414. Either way, that' a LOT of voltage :)

[@slyfoxx2973]

I dunno...I think allowing "Ripple" in my output tubes would cause some form of "electrical intoxication" leading to slurred notes, rhythmic irregularities as well as frequent bathroom breaks and possible lose of balance. Might even be a fire hazard!

[@UncleDoug]

Yes, but in case of fire, you could simply take the "bathroom break" on the fire.

[@montygore]

Hi Uncle Doug. You might think It is a lie but my wife taught our cat to fetch.

[@UncleDoug]

I believe you, Monty. Obviously, cats are capable of learning it.

[@moodyga40]

325 volts from centre tap to each side

[@UncleDoug]

+ian “valve doctor” forster It depends on the PT, Ian, but for most of the ones I work on, 325-0-325 is correct.

[@willthiessen6361]

Hey UD, do you have a Paypal tip jar?

[@UncleDoug]

We have a PayPal account, Will. The account address is [e-mail] Thanks :)

[@willthiessen6361]

Uncle Doug perfect. Will send something soonish. Buy some treats for Rusty and Jack. Your amp knowledge and teaching is great, but Rusty's camera work is even better! 😂

[@willthiessen6361]

done! get some treats for Rusty and Jack. They are are doing most of the the hard work, right? ;)

[@moses1202]

It’s 100v in the country I’m living.

[@UncleDoug]

I believe Japan uses 100VAC for smaller devices and 200VAC for large appliances.

[@moses1202]

@@UncleDoug most of the appliances are 100v, the only one that uses 200v in my room is air conditioner.

[@UncleDoug]

@@moses1202 How about the water heater, stove, and clothes drier ??

[@moses1202]

@@UncleDoug the rest were not in my room. water heater looks use 200v, we have only gas stove here but the portable electric one uses 100v and the embedded one should uses 200v. I’m living in a shared building which is more like student dorm. It was reformed into commercial share house from employee dorm of Mitsubishi heavy industries. Everything here in Japan is tiny.

[@UncleDoug]

@@moses1202 Thanks for the info, Moses.

[@biebikolu916]

Brian face mas

[@UncleDoug]

If you say so, BL ;)

[@MrMac5150]

Maybe you should stop Rusty, from hanging around Jack, he is shedding off his bad habits.

[@UncleDoug]

+MrMac5150 Just like he sheds his fur :)