The Effect of Output Tube Bias on Tone, Gain, and Headroom.....A Side-by-Side Comparison

There is a lot of conflicting information on the Internet regarding the effect of output tube bias on amplifier tone, gain, and headroom. In this video, I will set up comparisons to allow us to determine once and for all, what the truth really is. Using digital recordings at 40%, 50&, 60%, and 70% of max PD for grid-biased 6V6's, we will audibly determine the relative tone quality, then using an audio editing program we will analyze respective gain for each percentage, then using an oscilloscope we will measure the output power of the amp, just prior to the onset of clipping, at each bias percentage to see if output power (i.e. volume or headroom) is related to bias.
In our second feature we will analyze in detail, the differences between the classic AB-763 Blackface Deluxe Reverb circuit and each of the circuits found in the Silverface models made from 1967 to 1977. We'll see which SF changes should be reversed to achieve BF tone, and which should not.
If you enjoy advertising-free videos like this one, please SUBSCRIBE to our channel and consider becoming a Patreon patron at / uncledougsvintageamps or making a PayPal contribution to account: [e-mail] Thanks so much for watching and supporting our channel.
I am indebted to the fenderguru.com/ website for some of the schematics and insights presented in this video. Do yourself a favor and check out their excellent site for a wealth of information regarding vintage Fender amps.

[@grazioso58]

all i can say is: i wish i had teacher of physics like Uncle Doug when i was young

[@UncleDoug]

Thanks, G58 :)

[@hahaagi]

Me two.

[@jazzFABRYk]

Me too!

[@whitneyschuster2439]

you mean you wish your physics teacher taught you about tube amps?? yeah, me too 😆 for real though, Uncle Doug is an excellent teacher and that's a skill in and of itself, on top of his skill with tube amps. i bet he would make an excellent lesson on literally anything on which he is well informed.

[@petemitchell6788]

A grammar teacher would have helped more. 😂

[@johnqpublic2718]

I have learned more from @Uncle Doug about vacuum tube/valve electronics than I ever did working on my ee major. I can't thank you enough for all the work you do, sharing your invaluable knowledge.

[@jenniferwhitewolf3784]

He is a great teacher.

[@UncleDoug]

Thanks so much, Luke. It's really rewarding to hear that our videos are helpful.

[@UncleDoug]

Thanks, Jennifer. From you, it means a lot.

[@cacornett58]

Exactly, again the old saying, They don't teach you this in school. I have learned more in one month of Doug videos about tube amps, than I can imagine. Very well presented with everyday English language.

[@CC-te5zf]

Amen. I was a technician in the Air Force. I was trained in Electronic Principles twice, with years of other formal training for electronic and electrical; yet, I emerged from all that training without being able to explain how to bias something. I often marvel at my notes that I took - I recognize the hand writing, but I suppose I held that information long enough to pass a test then dumped it. And in a nuclear weapon system, the troubleshooting is very narrow and clearly defined. One must have certain certifications to troubleshoot beyond what the book says for obvious reasons. But - watching Uncle (Professor) Doug has blown the door open for me and I'm recalling things I learned ins 1984. And the best part of all: I'm having FUN! I retired a few months ago for medical reasons and dreaded it. Now, holy cow - I'm digging into this and having a blast! I should've retired sooner to do this!

[@julian65886]

Doug; you have the best radio voice ever-------and your dominion of the English language is astounding. I type this before I watch the whole video.

[@UncleDoug]

You are so kind to say so, JG. Thanks !!!

[@arnoldshaner3351]

@@UncleDoug You are right up there with the guy from Distinguished Spirits.

[@jwingo7257]

I hear a Gene Shepherd clone in U.D.’s voice.

[@UncleDoug]

ADDENDA: 1.) My use of the phrase "plate resistor" to describe the 4.7/3.3 Meg wet or dry reverb resistor is meant figuratively (i.e. to describe its function), not literally. 2.) My definition of "Clipping" was inadvertently "clipped" from the video. Here is a proper definition: Clipping is waveform distortion that occurs when amplifier output tube(s) are overdriven and forced to deliver an output voltage or current beyond their maximum capability. Clipping is highly undesirable in both SS and HiFi circuits, while it is often utilized in tube amplification to enhance guitar tone. Crossover distortion, however, sounds awful and is never desirable. 3.) Clean "headroom" is the term used to describe the maximum amount of amplifier output possible before clipping begins. Maximum RMS output power is routinely measured pre-clipping, i.e. clean headroom only. 4.) I inadvertently expressed the decibel scale as being linear instead of logarithmic, during my explanation of gain vs volume. I should have stuck with "volts" instead ;) 5.) A few viewers have commented on the audio quality during the bias comparison. Recall that this is a "recording of a recording" so any artifacts are essentially doubled.

[@PetraKann]

Excellent video Uncle Douglas. It appears from oscilloscope outputs that the crossover distortion shoulders are present at low and high amplifier output/gain. Whereas clipping type distortion occurs when the amplifier volume is cranked past a specific level. Can our ears pick up crossover distortion? Cheers from down under.

[@rjprivate]

Imagine the confusion at the electronic stores with lines of people asking for wet resistors. Demanding to get them, small riots breaking out. Anarchy. Society breaks down and cats take over the world

[@UncleDoug]

@@PetraKann Yes, indeed, Petra. Crossover distortion is quite noticeable and unpleasant.....as you can hear in the 40% audio clip.

[@UncleDoug]

@@rjprivate We might be better off in the long run, RJ, considering the current state of affairs.

[@jochenhaug3764]

@@PetraKann - I am pretty sure, your ears can pick up Crossover Distortion... It does not sound very pleasing - hence all the efforts to avoid it...

[@Finom1]

Bless you Uncle Doug for sharing your wisdom with us. I have always wondered how changing component values in the Tone Circuit effects the Tone and Frequency Response:) You are an amazing Educator and Instructor. I am a visual learner and you have always exceeded all my expectations. Your educational videos will be used as a historical reference archive for this generation and generations to come. Your an honorable and humble man spreading love to all your viewers. Great Karma in your community!!!

[@UncleDoug]

Wow, thanks so much, F1. We truly appreciate your very nice comments.

[@gwinn7830]

A great presentation as always. Hypothesis, experimentation, validation and calibration very clearly and concisely presented. Also room for the subjectivity that is real, meaningful, and at the heart of all music. Bravo!

[@UncleDoug]

Thanks for a very kind appraisal. Our goal was each of the criteria you mentioned.

[@adenihil]

Dear U.D : The quality of this channel is unmatched! Thank you so much for your generosity and willingness to share your knowledge with us. As usual : you the man! 🤘🏼

[@UncleDoug]

Wow....thanks so much, Adrien. Hearing from great viewers like you makes it all worthwhile :)

[@vadenk4433]

Love me some Uncle Doug in the morning. It’s 20 degrees here in Spokane and this upload warmed me right up.

[@UncleDoug]

Bask in the warmth of our output tubes, Vaden :)

[@drlonghair19]

@@UncleDoug} g 00 gold 9

[@hestheMaster]

If your looking for how to videos on building any kind of amplifier THIS is the right place. Congratulations on a wonderful explanation on this particular part of practical amp design Uncle Doug. You and Mr. Paul Carlson are the best teachers when it comes to electronics design on KZbin in my honest humble opinion!

[@UncleDoug]

Wow....thanks so much, HM. We really appreciate it :)

[@johnmarshall3903]

Doug, this is one of your best presentations yet. I learned a lot from this one, thank you!

[@UncleDoug]

Thanks so much. I really tried to make this a good one, and I appreciate your kind words.

[@mrsconley666]

I love when you go through schematics and explain in detail what is going on, etc. This is what makes your channel so so so special, your ability to teach in a very direct and understandable way, show us what is happening in the amps physically and then show us again on paper. Very comprehensive. I LOVE YOUR TECHNICAL VIDEOS TO DEATH.

[@UncleDoug]

Wow.....thanks so much, Sean. I'm glad the videos are clear and enjoyable.

[@michaelwebb4082]

I love your technical videos. I am almost confident enough to tackle an amp build myself because of how well you explain things. I’ve gone back and watched all of your old tutorial videos multiple times.

[@UncleDoug]

That's great to hear, Michael. It makes it all worthwhile for us.

[@kenhancock8931]

Thx uncle Doug . Your videos bring happiness and a light of hope lately. 2020 is the worse year so far in my life. Thank you so much. Hope you have a great day.

[@UncleDoug]

You're quite welcome, Ken. I don't think any of us would choose to relive this year, but hopefully 2021 will be a better one.

[@RHR-221b]

@@UncleDoug 👍 🎄 🍻 😎

[@GL64]

Also, yes, please continue the tech talk! I'm loving it.

[@UncleDoug]

Will do, GL.

[@russellsmith4615]

As someone who enjoys working on my own Fender amps but does so with enough knowledge to be dangerous, your videos help keep me out of trouble by being my first "Go-To" reference. I've learned so much from you and continue to learn something new with every video you post. Many thanks for sharing your knowledge, experience, and insights - it's a great privilege to be in your virtual classroom. And your 4 legged teaching assistants help make these even better! Bravo, and many thanks, Uncle Doug!

[@UncleDoug]

You're quite welcome, Russell. We're glad you find the videos to be helpful.

[@mp-ov9dh]

Love new Uncle Doug videos. I can never get enough of these. I go back to them all the time because there is so much info. This video is a treasure and I learned a bunch. Thank you!!

[@UncleDoug]

You're quite welcome, Mp. I'm glad you enjoyed it :)

[@olipito]

I'd like to add my extra upvote for the part2 of the video. I really enjoy this kind of content.

[@UncleDoug]

Thanks, O. Your vote is noted.....and appreciated.

[@weld4beer106]

Everyone out there in you tube land needs to see this.. absolutely broken down to the ground and built back up with full explanation for what you did. Then break down the differences between a 900 to 4+k fender amp . With fantastic guests commentary towards the clipping. Uncle doug busting there butts . Thank you . We all love you and wish you well . Cheers ! .

[@UncleDoug]

Wow.....Thanks so much, W4. So glad you liked the video :) Likewise on the good wishes.

[@michaelmcginley7412]

So great! Please keep up the 2nd half analysis. I'm learning so much.Thanks for all the great videos, Doug!

[@UncleDoug]

You're welcome, Michael. Will do :)

[@RobertWrightOneManCovers]

You're a national treasure, sir. After 2 days of searching fruitlessly for any useful content to help this first-timer bias a 1972 Earth B-2000 for its 4 new 6L6WXT+ tubes, I found your videos and not only biased the amp with no problem, I can now understand simple schematics as well as how tubes actually work. I can't thank you enough.

[@UncleDoug]

That's great news, Robert. We're really glad the videos were helpful.

[@VJRKC]

Mi estimado Uncle Doug, it is amazing the teaching skills you have, you was, if not in this life in some past, the best "Maestro" I've ever known or existed. Me quito el sombrero para saludarlo! Un fuerte abrazo desde Mexico.

[@UncleDoug]

Wow, thanks so much, Juan. We really appreciate your very kind words and wish you the very best :)

[@centerfoldstands2750]

That was excellent Uncle Doug! Thank You 👌

[@UncleDoug]

Glad you enjoyed it, CS :)

[@ringostarr4520]

Always love your videos Uncle Doug! Your approach to making these videos is very well thought out and educational. I have been going back and rewatching the older videos again during this damn pandemic. Sure makes the time go by more enjoyably. Keep on rocking those amps!!

[@UncleDoug]

Thanks so much, Ringo. Will do :)

[@VJRKC]

This type of video is the best educational and informative that I can remember. Your knowledge and also the level of documentation take the "class" to a level of comprehension that even a non-technical skilled person can understand. Great Job Uncle Doug!

[@UncleDoug]

Thanks so much, Juan. I sincerely appreciate your kind words and am glad you enjoyed the video.

[@JasonTHutchinson]

I always click the thumbs up on all your videos before watching them. I have learned so much from watching these.

[@JasonTHutchinson]

The amp sounded at it's best at the highest bias level tested. The bass tightened up, and the highs and mids sounded more defined. I guess I'm not too surprised by the results. The tubes were designed and engineered to run optimally around 70% plate dissipation. Anything below that did not sound great at all. I would say that 60% is even too low. I would be curious to hear what 65% sounds like. I'm also curious how it would sound at above 70% up to the point of redplating. Perhaps that test would be better done with a fresh set of tubes.

[@UncleDoug]

Thanks so much, Jason. I agree that the 60% to 70% range was the sweet spot. I doubt that going beyond 70% would yield any significant improvement in tone.

[@caryrodriguez7040]

i can definitely hear the goodness at 60% and 70%. Good looking DR you have there Doug! I have a Blackface DR myself and it's biased around 68% because that's what sounds good to my ears. Another excellent video sir! Many Thanks!

[@UncleDoug]

Agreed, Cary. The sweet spot varies but somewhere between 60% and 70% seems to give the best bang for the buck. Thanks !!!

[@richardpope9985]

Please keep 'em coming. I cannot believe how much more, I now understand, how amps work ! ! ! Your method of teaching is off the charts awesome.

[@UncleDoug]

Thanks, Richard. Will do :)

[@jagjet9153]

Bravo Uncle Doug! Once again you have added an insightful, technically important bit of content that should help everyone with their understanding of the best use of their amplifiers. You should continue with the technical series as it does give so much necessary information about various types of issues. Thanks again for all your efforts on our behalf about these interesting and important topics.

[@UncleDoug]

You're quite welcome, Robert. We will definitely keep producing technical videos.

[@Finom1]

Bless you Uncle Doug for another amazing educational video. We are all locked down, so we turn off the TV and turn on Uncle Doug's inspirational videos. We want more:)

[@UncleDoug]

Thanks so much, F1. We are working furiously on future videos for you :)

[@timclay2510]

Uncle Doug can you get me some schematics on your volt and amp meter that you put your tubes in to measure the amps and volts on the match tube.s@@UncleDoug

[@dale1956ties]

OK, who's the yutz that gave this a thumbs down. There's one in every crowd I guess.

[@UncleDoug]

Perhaps it was a leper whose nose detached from his face while coincidentally over the thumbs down key ;)

[@v12dot]

3 now , it’s a beak fest of epic proportions:(

[@shekador]

@@v12dot maybe they're just biased against this video for some reason

[@iroffman]

They saw "Headroom" and thought it was porn.

[@kbkman7742]

I don't know who thumbs down any uncle doug videos but there are some real spiteful people in the guitar/amp tech world

[@oimate4201]

The double feature was great, Uncle Doug! Thank you for another top quality video!

[@UncleDoug]

My pleasure, OM.

[@michaelbutler2312]

both parts were great. i'm so impressed that you not only show that there are bias differences but that you are also open to change your mind based upon your testing. and, the differences in the circuits was very educational. thank you! i'm lucky i have a 66 deluxe reverb that everyone who plays it won't play any of my other amps!

[@UncleDoug]

Thanks so much, Michael. I appreciate your kind and accurate comments. You are a lucky guy to have such a great amp.

[@GilgaFrank]

Always good to see someone dispel amplifier myths and half-truths through the application of science. Maybe next you could convince guitarists that measuring DC resistance of pickups in isolation doesn't tell them anything about the output voltage!

[@UncleDoug]

Thanks, Frank. I'll keep your suggestion in mind :)

[@forthwithtx5852]

Unless your dream amp (circuit) already exists, or you’ve already built it, I’d like to see you build one. All the bells and whistles. I’ve seen about 90% of your videos now. Going into reruns to reinforce what I’ve learned. I bought a late 50’s Stromberg Carlson AU57 PA amp and had the schematic blown up to blueprint size. It has 4 inputs, 5 12AX7’s, 2 6L6G’s, 2 12AU7’s, a 5U4GB, and a 6X4. I’m not sure if I’m going to restore it or turn it into something else at this point. Should be an interesting winter project.

[@UncleDoug]

Thanks, FT. I think a Princeton Reverb is pretty close to my ideal circuit.....great tone and effects but not too bulky. Good luck with your project.

[@jeffsullins7555]

That was an outstanding educational video that described complicated electronic principles in a way a layman can understand and it answered so many questions that Fender lovers have wondered for years...you should be proud of yourself Uncle Doug.....thank you for the knowledge...Keep up the great work!!

[@UncleDoug]

Thanks for your very nice comments, Jeff. We will :)

[@DetroitWrecker666]

This video is one of the most useful videos on KZbin regarding this subject. Thank you SO MUCH for doing this, and clearing this up. You're awesome!

[@UncleDoug]

Wow, thank you, DW :)

[@TimBinns68]

I definitely think the 40% sounded clippy but above 50% it started to clean up. IMO 70% sounds best, maybe that's why that's they suggested 70%.

[@UncleDoug]

Agreed, Tim. The 70% recommendation does seem to be the best. Now we can actually understand why.

[@codezero6023]

Cross over distortion is very audible

[@duncan-rmi]

have I missed the link to the actual recording used for the test? :-/

[@hallanvaara6106]

This video is a classic already.

[@UncleDoug]

Thanks, H :)

[@zopilotesky3014]

Both portions of this video were excellent. Part 2 especially. Thanks so much for explaining the reasons why the changes were made. It's a big help in understanding these circuits. Repetition is the key to learning!

[@UncleDoug]

Thanks, ZS. Glad you enjoyed the video.

[@jeff7807]

Very interesting and informative video. Great job Uncle Doug, Thank you for going the extra mile.

[@UncleDoug]

You're welcome, Jeff.

[@guitarsofold100]

Excellent presentation as usual Uncle Doug, could you expose the Dumble myth as a fact or fiction?!

[@UncleDoug]

Thanks, John. That's beyond my ability at the moment. I would have to get my hands on a proper Dumble amp in order to make any legitimate observations.

[@johnsimms3957]

I'm thinking 65% dissipation may sound best. Might EL34s be different than 6V6s when it comes to optimal tone?

[@UncleDoug]

It's a personal preference, John, and yes, I think different tubes respond differently to bias levels.

[@thomasburnett4712]

Bravo Uncle Doug! What a masterful tour de force tutorial! Thank you so much for using a rigorous application of scientific method to dispel the subjective opinions that constitute conventional wisdom regarding the sound qualities of Fender amplifiers! I also really appreciated the in depth analysis of circuit differences and their consequences for the different variations of the Blackface and Silverface Deluxe Reverb models. This video is truly a gem and you Sir are a generous and valuable national treasure!

[@UncleDoug]

Thanks so much, Thomas. Comments like yours make the effort required for videos like this all worthwhile. I sincererly appreciate your kind words.

[@brucebuckeye]

Very well explained! I enjoyed both parts! Yes, please continue the schematic comparisons! God bless and stay healthy!

[@UncleDoug]

Thanks, Bruce. Will do.

[@ericst-louis110]

Kids should listen to your channel just to learn how to speak English.

[@UncleDoug]

Thanks, Eric :)

[@MichaelBeeny]

Yes Doug, you need far more LIKES, you knows, init's then children will also understand you!!

[@frmcf]

@@mrman3565 The first recorded use of 'kid' as a colloquial term for 'human child' was in the 16th century. By the time Charles Dickens used it in 'Oliver Twist' it had been in use for over two centuries, so yeah, I agree that it's a bit early to accept it into the language just yet. Let's give it another 400 years or so and see if it sticks.

[@UncleDoug]

@@circusbrains Yes, indeed, CB. I was a classroom Math & Science teacher for many years.

[@UncleDoug]

@@frmcf Well said, McF :)

[@jenniferwhitewolf3784]

School is in session! Great way to start the day. In the hi-fi world, when designing an amplifier, a lot of work goes into deciding where you want to 'specify' the bias point, as it sets how much Class A region ( lowest distortion) you have and how much power you can deliver, and how the idle current will effect the tube life. Take note youtube viewers, this IS meat and potatoes tech, teaching the REAL facts and how engineering choices alter the sound of an amplifier. In the hi-fi world we not only listen, we use test signals and distortion analyzers. Right now I am designing a push-pull 6BQ5 amplifier output stage. It is going to be switchable between triode and ultra linear pentode modes, and have a 2 position bias switch, allowing choice of shorter tube life lowest distortion larger Class A region, or for less Class A overlap giving longer tube life and a few more watts, at the sacrifice of slightly higher coloration.

[@UncleDoug]

Thanks so much for your very knowledgeable and informative input, Jennifer.

[@bluesteel48]

Hi Uncle Doug, all I can say is this was awesome. Wonderful lecture and super labs. Thanks so much. I feel the extended videos are great and hope to see more of them. Please stay safe and stay well. Regards, Steve

[@UncleDoug]

Thanks so much, Stephen. We will......you, too, I hope :)

[@larrydering1598]

Like others have said, I learn more here than all the study materials available period. Thanks Doug for your detailed information and resources.

[@UncleDoug]

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

[@shyammohabir8283]

Every Video from Uncle Doug is "Classroom in Session"

[@UncleDoug]

Thanks, Shyam. I hope the "classes" are enjoyable :)

[@jayster.k.wiseguy]

little hair on the peach at higher volumes~

[@kressimentto]

Mr Doug, I'd really like to call you a master of knowledge transfer and I really think you have a gift! Your videos are great in so many aspects and they are a jewel for anybody that knows how to recognize it. Best regards and please do keep up the excellent job. With great respect, Kreso

[@UncleDoug]

Wow, thanks so much, Kreso. We will :)

[@dogbarley7178]

Hi Uncle Doug, your latest video couldn’t be more timely for me. The day before this video dropped, I picked up a ‘74 SFDR with a serial number just a little lower than your amp. Can’t wait to open her up to see which circuit I have! The explanation of what each change does frequency/voltage-wise is so incredibly clear & valuable. You, sir, are literally a amp tinkerer’s Godsend! Thank you from a very grateful viewer & Patreon supporter. DB

[@UncleDoug]

That's great news, DB. I'm glad the video was helpful and wish you the best with your investigation.

[@dogbarley7178]

Hi again Uncle Doug, it appears that my ‘74 SFDR is the A1172 circuit. The PT does NOT have a 6.3v CT wire (but does have factory virtual CT set up). Very odd mystery. The standby is also wired pre-reservoir caps (which I am fixing right now.) Thanks again for this invaluable circuit analysis!! I am grateful for you sir! Merry Christmas, DB

[@jayster.k.wiseguy]

hearing trouble with the spectrum, as if pieces of the sound get eaten~

[@marblelee]

The interface and the daw may be clocked differently.

[@UncleDoug]

Yes, that happens a lot ;)

[@damagestudiosca]

Thank you Uncle Doug. You made sense out of the hours of videos with conflicting information and over or under technical detail and just plain nonsense that i have endured trying to learn the skill of tube amp biasing. This is the last video i need to watch on the subject, i wish it had been the first. Thank you Sir.

[@UncleDoug]

You're welcome, DS. We're glad you enjoyed it.

[@phillipyannone3195]

I obviously missed this video when it first came out. I most certainly enjoy the technical review and analysis of these circuits. Although I am not a musician I am fascinated by the technology and your love and enthusiasm for these Fender Amps is contagious. Thank you for sharing your vast knowledge of these beauty’s, I have learned a lot from your videos. This is a keeper and I will revisit it again.

[@UncleDoug]

Thanks for your kind words, Phillip. Glad you enjoyed it.

[@tremelo68]

Another excellent tutorial on Bias and circuit changes from Blackface to Silverface! Thanks, Uncle Doug.

[@UncleDoug]

You're welcome, T. Glad you liked it :)

[@danieliiiadeva8368]

Uncle doug your channel is just so awesome. Whenever I have a question about tube amps, you always have a video for it. And yours always has the best explanation!

[@UncleDoug]

Thanks, Daniel. We're glad you enjoy our vids :)

[@oldguy5381]

Thanks for all the great videos this year. Hope you and yours have a merry Christmas.

[@UncleDoug]

It was our pleasure, OG. Likewise :)

[@carloschafin9144]

Excellent comparison of the black face vs. silver face versions. Super informative. Thanks a million as always Doug!

[@UncleDoug]

You're welcome, Carlos. Glad you liked it :)

[@patricklozito7042]

This presentation is outstanding! Yes, please continue such subjects.

[@UncleDoug]

Thanks, Patrick. Will do :)

[@chrisjackson2212]

You're so right! It's all about TONE! Thanks so much for all of your incredible work. You're a true inspiration for anyone that's into valve amps. I keep watching some of your vids over and over again because they're so compelling and there's so many nuggets of knowledge there. I always look forward to what you're doing next. If you ever get your hands on more British amps such as Orange, Vox, Marshall, I'm sure we'd love to see what you think. ATB and give those naughty kitties a good old stroke from us over in the UK!

[@UncleDoug]

You're quite welcome, Chris. Thanks so much :) I hope to get a 60's Vox in the next few months.

[@lazarsfiftythree8996]

Thanks for another great vid uncle doug! Youve been teaching me about amp science since i was an 8th grader and im 20 now!

[@UncleDoug]

You're welcome, LF. You're making me feel old ;)

[@jdmccorful]

Great deep discussion of circuits' changes.Through explanation of "headroom" , which was new to me. You made it quite understandable. Long but enlightening. GOOD education. Thanks.

[@UncleDoug]

You're welcome, John. I'm glad it was helpful.

[@clydetaylor2448]

best electronic teacher/engineer I've heard explanations spot on. I have qualification in industrial electronics all for solid state micro processors and digital I always wanted to learn about vacuum tube technology and now I have learned from the master. I am now servicing my own valve amps and building valve equaliser preamps. You do have the best voice, very therapeutic.

[@UncleDoug]

Thanks so much for your very nice comments, Clyde.

[@jeffkellogg76]

As always, EXCELLENT VIDEO. Tons of valuable information that applies to any tube amp. Great Reverb information as well.

[@UncleDoug]

Thanks so much, Gonzo. Glad you enjoyed it :)

[@butchlauer]

Hi Uncle Doug, Man did I get warm and fuzzy when I saw that silverface deluxe reverb. I am 56 and seeing your amp was one of the best flashbacks a guitar slinger could have. I realise I'm more of the pull boost era of 79 or so, but the deluxes are some of Leo's greatest accomplishments. Thanks for all you do.

[@UncleDoug]

You're welcome, Phil. I agree :)

[@stoneybologna186]

After watching Uncle Doug’s videos all other content pales. Thank you for making these, Uncle Doug. I feel like I learn more and more even on the 10th+ rewatch.

[@UncleDoug]

Wow.....thanks so much, Stoney.

[@stevepiper9034]

I thoroughly enjoy your "Technical Second Features" as you described at the tail end of the video. I actually enjoy watching all of your videos, you speak my language. Thank You for your work!!

[@UncleDoug]

You're welcome, Steve.

[@sixstringsofjoy9053]

always such a pleasure to watch a man at the height of his expertise demonstrate in a kind ,organised ,and well worded challenge to amplification lore.

[@UncleDoug]

Wow, thanks so much, GL :)

[@kennethgroves6552]

Thank you Uncle Doug. I totally understand what you explained. A true professional teacher. Good on you Sir.

[@UncleDoug]

You're quite welcome, Ken. Glad you enjoyed it.

[@tomjust7421]

Just this morning I was thinking "It would be great if Uncle Doug developed some new circuit tutorial videos". I checked to see what you had uploaded recently, and I see that this one is fresh out of the oven! I have suggested your tutorials to a number of folks interested in learning about tube amp circuits, and the reviews have been universally positive. They were essential to getting me started with circuit design a few years back, and I think they're the best of what's out there on the subject.

[@UncleDoug]

Thanks so much, Tom. I'm glad you enjoy them. Next will be a BF/SF comparison of the Super Reverb.

[@suomi35]

I enjoyed both first and second features, as usual. Thank you, Uncle D!!

[@UncleDoug]

Glad you enjoyed it, Suomi :)

[@jayster.k.wiseguy]

wow, such subtleties~ thanks for taking the time to figure all this out for us~

[@UncleDoug]

our pleasure, Jay. Glad you liked it!

[@ReFretted]

Another terrific learning experience. Thank you Uncle Doug.

[@UncleDoug]

You're welcome, ReF. Glad you enjoyed it

[@rmg471]

Wonderful experiment, Uncle Doug. Just the facts. You’re a treasure.

[@UncleDoug]

Thanks, Ryan :)

[@koulis70]

I ve been watching your videos and find them extremely informative and useful. I would really be happy to watch you talking some day about the , not so clear , subject of Grounds and proper grounding techniques in tube amplifiers.:-)

[@UncleDoug]

Thanks, Mark. I'll keep your suggestion in mind for the future.

[@framusburns-hagstromiii808]

Learned all of this 43 years ago....but never really 'got it' until I watched this! Really appreciate your straight forward, logical approach. When I went through tech school we always got wrapped around the axle with all the math and technical jargon and the practical application kind of took a back seat. The info was there but we were more focused on passing certification exams than actually understanding how it worked in real world applications. Thanks Uncle Doug!😀😀👍👍

[@UncleDoug]

You have described the shortcomings of most formal education, FB. It tends to exist to provide certifications rather than genuine knowledge. It was our pleasure :)

[@framusburns-hagstromiii808]

@@UncleDoug Agreed. Spent much of my working career chasing various 'certifications'...FCC , Novell, Microsoft,Cisco, Watchguard, etc. Most were sorely lacking in practical real world application...Thanks again!

[@jerryhatrick5860]

This channel is keeping me awake all night. I wish all this info was out many years ago when I wanted to do this kind of work a lot more. I work on my own amps well enough but not to this depth. I can't seen to stop watching video after video. Nothing better to do anyway lol.

[@UncleDoug]

We're glad you find the videos addictive and helpful, Jerry :)

[@ima640]

Great video, takes me back to my college days. love the technical second feature, and the development fo these circuits.Thanks for sharing your knowlege and experience.

[@UncleDoug]

Thanks !! Glad you enjoyed it, Ima.

[@cassvirgillo3395]

Hello Uncle Doug & Family, A new Uncle Doug video always makes my day. Been working late nights, so, a little late viewing, when done and home, I'm tired and thinking sleep. It did sound cleaner as the PD went up, at least to me. You can't help but learn a great deal from your most excellent tutorial videos. Voltage, squared, divided by the ohm's of impedance will equal the watt's of output, as learned from you, and, John Audio Tech on KZbin, an excellent channel well worth a view, where it is solid state chip amps, John is very knowledgeable and has a lot of good information. What a great experiment and explanations of the tests and the results. As we should know from watching you, it's all about the tone, like a sweet sounding, lower watt single ended amp. Great video. Glad your doing well. Still commenting, you know what that means, still kickin'. Wishing you and yours a Happy Year End, Christmas, if you do it, and, all the best in 2021, Cass.

[@UncleDoug]

Thanks so much, Cass. Likewise to your and yours for a great Christmas.

[@greenyodamaster]

Thank you for yet another great video. I feel inspired to go through my amp collection and do a similar analysis. With my ears getting older, a scope analysis may yield new results. I would however inject the input signal (possibly pre-amplified by an external transistor-based booster) directly into the phase inverter to make sure that any distortion resulting from overdriven preamp-tubes is eliminated.

[@UncleDoug]

Sounds like a worthy experiment, TSX. Good luck with it.

[@JanLarsenFredriksen]

The dear old uncle from the heaven of tube knowledge and pedagogy did it again. thank you so much for making these wonderful videos. So much knowledge put in to a beautiful package of clear and precise language and no nonsence methodes. Easy to skip x-mas shopping :-)

[@UncleDoug]

Thanks so much for your very kind words, Jan. We really appreciate them :)

[@ReneStover]

Nothing like a Practical mind for solving problems and teaching others, and Uncle Doug, you have a great practical Mind, thanks!

[@UncleDoug]

Thanks so much, Rene :)

[@cougar1861]

Excellent lesson in scientific methodology applied to tube amplified audio! Yes, please, MORE of these technical "second feature" videos. JP

[@UncleDoug]

Thanks, C. Will do :)

[@golgothaassassin5035]

Thank you Uncle Doug, I really Appreciate you going into such detail, I'm leaning everyday from your videos.

[@UncleDoug]

That's good to hear, GA.

[@Ideal1980]

Great video, Uncle Doug! Knocked it out of the park as usual.

[@UncleDoug]

Wow.....thanks so much, Ideal.

[@thomjmoore]

Love this content. Please continue when possible.

[@UncleDoug]

Will do, Thom. Thanks :)

[@hotbrakepads]

Thanks so much. Finally data driven results showing what cold vs. hot biasing does. 👍

[@UncleDoug]

You're welcome, JM :)

[@alanbrower9969]

Great video Doug! Yes to more of everything!

[@UncleDoug]

You got it, Alan. Thanks !!

[@russellburdick]

Loved the science on the Tube Bias, and the circuit change info. Thanks Uncle Doug!!

[@UncleDoug]

You're quite welcome, Russell.

[@straggsmcstraggle6212]

fantastic & very informative, best video iv'e seen in ages, thanks Doug

[@UncleDoug]

Wow, thanks, Straggs.

[@DoctorCalabria]

Excellent topic with a peerless presentation. Thanks again Uncle Dave and et. al.

[@UncleDoug]

Thanks so much, Frank. Glad you enjoyed it.

[@darthbubba866]

Thank you for a "once-and-for-all" demonstration of what we all kinda guessed was true. 👏

[@UncleDoug]

You're welcome, Darth. Sometimes it's good to evaluate and confirm or discredit suspicions :)

[@MrsG7swr]

i have to commend you highly for the time and effort taken to make this very informative and educational video.

[@UncleDoug]

Thanks so much, Mike. Glad you enjoyed it

[@rjprivate]

Thanks for the great video. Bias is so important. I always tell my friends "bring me any great amp and I can destroy its sound by a wrong bias"

[@UncleDoug]

Well said, RJ. You're welcome :)

[@3MonkeysGarage]

excellent work. From a pair of shall we say, abused eardrums, I could notice more clarity and definition as the bias went up. And audibly, to me, it was distinctly better at and above 60 % and 70% seemed better. At the end of the first set of sound clips, I jumped the video back to the 40% to be sure and then to the 60%. I think you are right on it with 70 %. And then you probably move into diminishing returns zone. I really appreciate the time and effort you put into this. We can check off another box on our fact sheet.

[@UncleDoug]

Thanks so much for your careful evaluation of our video, AZ.

[@Ten80pete]

I think I speak for everyone when I say we greatly appreciate you using the dummy load, Doug. I also want to echo the sentiments of the other commenters and add that as someone who only recently started to gain (pun intended) an interest in the science of amplifiers, this exhaustive test/explanation/lesson on both an objective AND subjective front, you left no stone unturned and I didn't feel as though I was expected to fully understand a litany of technical vocabulary to learn from you. The long and short of it is this: Thank you for being a great teacher!

[@UncleDoug]

Thanks so much for your very nice comments and observations, Peter. I'm glad the video was helpful.

[@gustavoloebel]

Such a great class of audio, tubes and electric math! Thanks for sharing so much! 👏👏👏👏

[@UncleDoug]

Glad you enjoyed it, Gustavo.

[@davegeetarwrist5597]

Hi from England...heard about Uncle Doug's" valve channel" only this evening from a friend.We both have a collection of valve "babies",Fender blues juniors,Vox AC15's,Peavey delta Blues,and right back to a 1958 Watkins dominator...I am amazed at the wealth of information that is available here...an absolute gold mine for us" tone hounds"....and delivered with an authority and conviction that is easily absorbed,even if you don't have a major in electronics ..thanks Uncle Doug,keep them coming....and Stay Safe.......Dave ..midnight and still watching!

[@UncleDoug]

Welcome to our channel, Dave. All "Tone Hounds" are welcome :) Have a great holiday season.

[@stratcat4450]

Thank you for the tremendous amount of work that you did to put all this great info together. I love all the proof that dispels all the disdain for the silver faces out there. If I ever needed that kind of volume again I'd be very happy to find a deal on one.

[@UncleDoug]

You're quite welcome, SM. Thanks for your nice comments.