Cathode Bypass Capacitors: How they Affect Gain and Tone 

Watching this in 2023. Congratulations on this significant milstone and thank you for being so generous with your knowledge!

I'm retired now and finally getting back to trying to teach myself elctronics. Your vids are the best. You sir are a great teacher

That sneeze by Rusty had me giggling. A very late congratulations on 100!

This is one of the most informative RU-vid channels I've ever seen. I'm just getting started repairing old amps and would be totally lost withOUT these videos. THANK YOU!

Happy 100th Doug, What a cool video, and explains the CBC very elegantly.

You can effectively voice an amp without any traditional "tone stacks" simply by selecting the right cathode and gain stage coupling capacitor values. Tone stacks lower your gain and they dampen the amps chime. Single-Coil pickups require larger coupling cap values - 0.1, 0.047, 0.022 and humbuckers sound their best with lower values - 0.01, 0.0056, 0.0047. Fender built his amps for his single-coil guitar line, therefore the 1k5 cathode resistor and the 25uf bypass cap, so that they sound full and not thin. The Marshall line sounds best with humbuckers, hence the 820 ohm with the 0.68uf arraignment, in order to manage the low end harmonics, especially when pushed. I often place a switch on the first gain stage in order to select one or the other.

I am going thru your older videos and trying to absorb all your lessons. I think i will need multiple inoculations as it is pretty new to me, but you method of sharing is just so damn good. it is a fun learning experience. Thank You Dennis

Thanks again, Doug, for the well thought out and presented tutorials on demystifying the tube amplifier.

Excellent again and thanks for sharing your wisdom, congrats on 100 videos!

Wow! Congrats on the 100th video Uncle Doug, I must say I've seen and enjoyed most of them!

Happy 100th anniversary to you and Rusty!

Thank you for going into this in detail. Very much appreciated!

Not just "a 100th video"... 100th of 100 awesome, super helpful, videos!! Crank it up Uncle Doug and Rusty, all the way up! :)

100th Congrats, Doug!! And thanks always for making amp goings on understandable to folks like me. ;) Cheers from Japan!!

Doug, this is fantastic you give us private lessons on something that we could never learn any place else! Simply amazing, I can't thank you enough. Keep up the good work..... and make Rusty do something okay

Congratulations UD. Your first hundred have been invaluable for all us circuit board curious musicians.

Congrats on the 100th vid! I am happy to say that with the great information from your videos and hours of research, my own Champ clone will be coming to life pretty soon. Thank you for the the high caliber videos and wealth of knowledge that you are passing on. Keep up the great work, and pass on my compliments to your outstanding videographer, Rusty. Best Regards!

Watching these videos all night..good stuff! Well done too.

Hi Dough, a warm thank you taking so much time to produce all this videos! I really like it and it inspired me to build my own amp. I'm desperately waiting for your next meeting!

Another excellent piece of teamwork! Thanks Uncle Doug for the very pleasant lesson and Rusty for the solid camera work.

Great video Uncle Doug, keep up the good work & congrats on the 100th video milestone! Now I am anxious to start tweaking the values of the cathode resistors & bypass caps on my amp.

Man. These videos are great. I have about 1,000,000 noobie questions I'd like to ask. Thanks for the vids and congrats on #100

Congratulations on passing the 100 mark. Really enjoying your videos and appreciate Rusty's contribution!

Congrats on the 100th video! We love you! Send Rusty my regards. =)

Great video Doug !! I learned a lot !! Thanks a ton for all you do !!

Hey Doug and Rusty, congratulations on the 100th video! I came across your channel a few weeks ago and was instantly hooked. I think I must have watched nearly all your videos! With your help and a bit of my own research I've been able to have a look around inside my current amps (nothing vintage but still a learning experience) and have started sourcing parts for my own vintage clone. Just wanted say thanks. Keep the videos coming!

...........always happy to see rusty provide his usual assistance and supervision........ ;-)

Hi Uncle your info and teaching on guitar amps is very helpful. I have been adjusting things in my 1960s blackface fender champ. I use it. At mass in church so I can hear every one else through it by putting a low signal to the amp from the sound board. Works good as an extra monitor. Thanks for all your Help. Dwight Allenpark,mi. near Detroit

Excellent explanation, Thanks!

Nice job Doug .. a very informative vid for #100. Looking forward to the next 100.

These videos are amazing, thank you so much for your effort! There is something about the way you explain things that makes it so much better for me to understand than any other resource I have found! Greetings to Rusty and Jack

The last part of this video, with the screen shot of the calculator program with graph, was fantastic. Thank you for all of your work.

Another good one! Thanks Uncle Doug and Rusty!

Thanks again Uncle Doug for your relaxed matter-of-fact deliberation style. I always learn something significant from your videos.

i never said thank you for all of this, you really helped me out in the earlier days.

Congrats on the 100th video and thanks for another clear and concise tutorial. You are, as already stated, a gifted teacher.. Thank you.

this is REALLY helpful......thank...

Rusty steals the show. Not just for guitar amps, your videos have helped me understand important concepts that apply to stereo and radio tube amplification. Eagerly awaiting each of your next 100 videos, congrats.

Thanks a whole bunch for the link to ampbooks.com - great resource!

Your videos are the best Doug. You explain so well even I can understand. Thank you

Great video and thanks for the link. Very helpful to many of us I'm sure.

Thanks again Uncie Doug you are an excellent teacher!

Congratulations on 100 of the best videos about tubes and related! A surprising amount of emotion shown by Rusty, whose camera work is first class. The hand acting with dramatic backlighting has reached a new zenith! :)) I might have to add a bypass cap to my 5F1 now.

I just wanted to say congratulations on your 100th video and thank you for your time and energy, and knowledge you put in to making these videos. I spend way too much time on youtube watching videos that interest me. Might I say, I have learned a lot watching your videos and I look forward to each and every one. I don't know you, but I like you. Thank you friend!

Thankyou so very much for all your video's Uncle Doug - All of us amp building madmen appreciate your contribution to this beautiful art form.

Thank you TubCal for that wonderful explanation. Through Uncle Doug and his subscribers I think I have found a tube amp Gold Mine!

Very cool stuff once again

Thank you for all of your time and knowledge

Congratulations for your excellent 100th video which you performed beautifully well described with very practical examples , as usual. Thanks .

From 4k to 87k... Called the Law of Accumulating Returns. (Great bit of kit, by the way. The biggest library ever does have some gems hidden in the landfill).

Excellent video's, well presented, and a world of information. I have looked at many of your videos on the subject of valve amplifiers and written pages of notes from them. My regards to Rusty and the cat.

I forgot this: *celebrating your 100th episode!* and *bless you* Rusty! Excellent video -- as it is a nice and easy lesson about of what a common cathode operation point is basically all about...!

Another great and informative video!

Excellent Vid! Wow, 100th video and still no ads! Very generous of you Doug. I once aquired an early Mesa Boogie schematic and found the first two gain stages had diodes in place of the Cathode resistors. So I tinkered with my 65' Deluxe Reverb using 1N914's with different capacitors (the schematic did not show any part numbers for the diodes). Using my Telecaster, I found some interesting gentle overdrive and sustain effects.. Eventually I went back to stock preamps but the OT-NFB circuit is another story...:) Still enjoy giging with my little sweetheart!

I am a self-learning electronics, I love old tube style amps and your videos helped me a lot understanding how they works, I have seem them once and again. I just build small tube-type circuits emulators (jfets instead tubes) cause is not easy to get components or build something here in Venezuela but I hope someday to build a nice 5F1. Until them I'll keep watching your videos and taking notes.

Wow... to think I was gonna leave that out of my 5f1 champ build... I probably would've been pretty disappointed with the sound. Very helpful!

Another great job!

Thank you for this video, it was very informing, I had never thought of this online calculator before

im late cause i just found you recently and im binging.. congratulations on 100 !!!!!

Another great informative vid! Plus, Rusty juice too! LOL! Happy 100th, now on to the next 100.......

Great teachings on tubes and amps. You have really helped my understand the mechanics. 72 k subscribers in 2020, Glad your channel is still here!

brill videos thanks for takeing the time so good

If I've not said it before, just wanna say your vids are clear, beautifully done and even make me feel I may still have a workable brain... Thanx so much and best to all of you and yours from us and ours... cheers

I'm slowly gearing up to build my first tube amp. A champ with your variable feedback modification. These series of videos have generated many pages of notes and many more ahhh moments. Thank you!

Very useful stuff here. Thank you Uncle Doug

Awesome video! Thank you!

Thanks, great calculator link!

Doug and Rusty :-). your lessons are just rocking. Totally focused on the spot. Not the usuall blabla. You have deep, very deep knowlegde about the stuff you are talking and you have the gift to explain complex things in an easy way and not "oberlehrer"- ly (you have to look that word up). I appreciate all your videos and keep the good work up... you guys are just AWESOME !!!

Enjoyed the video very much!Bob

Congrats on your 100th. Love the website calculator. I unusually use a decade box. This is much easier. Plus it has more choices than the box.

Thank you for the video! The info was very useful for building a Eurorack-format tube preamp module.

Thank you for a very informative video. I’ve bookmarked the calculator.

My Quest has ended. Perfect information presented perfectly! Thank you very much.

Thanks!! Great video!

You inspired me to drag out an old project that's been sitting in my closet for a couple years now. Just sprung for 70 bucks in parts. 🤦 Your videos are all over my RU-vid videos feed, so I suppose that's some kind of message the universe is trying to send me, lol I do watch your videos from time to time, but boy are you in my feed a lot lately! I thank you for the very informative tube amp videos ☺️

Curing cathode constipation without a laxative one cap at a time. Thank you Uncle Doug!

Amazingly useful and interesting. Thank you!!

thanks to u uncle doug for sharing your knowledge this is my favorite channel on youtube btw

Another great vid, Uncle D! I've never thought too deeply about this, but now I understand exactly why the income signal is almost always connected to the grid of the triode, and why your signal gets hotter (or louder) the harder you strum the guitar, due to the signal becoming more positive, which caused the grid to do less suppressing of the signal. Prior to this vid, my only thought on this was "signal hits the grid, amplification happens". I'm always surprised by what I learn watching your vids!

Thank you Doug.. great info...

Yeah! The 100th video. Time to party. Time to thank you again for your work, your just awesome! :)

Congrats to the 100th from Austria.

Just subscribed thanks so much for sharing your knowledge. I will be spending a lot of time learning from you.

Hi Doug...and Rusty too, This reminds me when I owned a Sunn Sentura II and was in the process of replacing some bad caps with audio grade caps which were somewhat expensive. Anyway after talking with an Engineer at Fender/Sunn I discovered the use of a bypass cap at the cathode. I don't recall what value was used but after I installed it I noticed a marked improvement in the high end response. The amp sounded much clearer and had some sparkle to it that it did not previously have. These were all audio grade caps that I bought at some expense...they still are expensive and really don't recommend using them unless you want to end up with something like an overpriced boutique amp. Anyway, I appreciate all your videos as they fill in a lot of blanks compared to when I went to school for electronics. Cheers and Merry Christmas.

thank you for sharing your knowledge and wisdom kind sir.

I know next to nothing about electronics, but you explained this in a very understandable and educational way. The link to the other website is appreciated. I will be subscribing to your channel and look forward to learning more!

Doug- As luck would have it, I've been trying to find info about the relationship of cathode bypass caps for days, and here you are with the perfect video! I'm a visual learner and thinker, and I have to tell you, I've been reading and studying theory of amplification for a while, but I've gained more practical knowledge from your videos than from any other source. This gives me the best overall comprehension when paired with the theory I've been trying to grasp. Thanks!!!

That you Uncle Doug and you to Jack, like all your video’s they are very interesting and informative. It’s amazing how much the cap values change so much in the way of tone. I just replaced all the 25uF cathode bypass resistors in my 67 Pro Reverb because the originals were all reading 36-38uF and now the amp sounds totally different. Previously I had to use the bright switch to get it to sound decent, it sounded muffled with it off. Now it sounds better without the bright switch. Highs and lows are so much defined and alive. Just figured out the bright switch isn’t heeded anymore and thats why I wasn’t happy with the results of the new caps. Everything is good now.

Thanks Doug, as an Electrical Engineer (guitarist) your explanations are great and sometimes amusing but keeping away from the maths helps a lot. In my student days (50 years ago) everything started with maths making the understanding of what circuits did exhausting to understand. I love your method learn to walk before you can run, thanks again.

Dear uncle Dough, thank you for all of your videos, especially educational ones. I had at home old, rotten music box: Jubilant 1101A made in 1958 by Tesla. And thanks to you, I was able to fix original final amp stage and even build my own preamp and tone stack for it. It is no masterpiece by any means, but it freakin' works and I am thirlled with joy, especially when a few months back, anything more complicated than a switch was out of my league.

This was your hundredth vid and you were happy that you had over 4,000 subscribers. It's a tad more than that now :o) Great site. I visit it daily.

Great video thanks 😊

Brilliant! Thanks

Greetings Doug and Rusty. Your amazing videos from even a decade ago are still so very enlightening. You are the Guru in this amazing technology especially in the art of teaching in a refined simplistic style. Wonder how the superstars Rusty and Jack are keeping these days....

Happy New Year Guys! Last month, I bought myself a 1974 Fender Twin Reverb (Silverface). All the original 1974 parts inside including the transformers and caps. Sounded beautiful with that distinctive Twin Reverb punch and tone. Like everything I buy, I had to open her up for a look see. I noted one of the brown electrolytics (Mallory 20uF 500V) in the dog-house had long spilled it's guts, yet the amp performed flawlessly, no hum or power supply issues. I figured it’s time for a capacitor change out, so I ordered some F&T's for the doghouse and IC 22uF 25V for the cathode bypass.. Once done, I found the amp lost it’s Twin Reverb lustre, something was tonally lacking. I figured it could not be the power supply caps, and decided to re-install the old, white Mallory 25uF 25V cathode bypass caps. Wow! That wonderful Fender Twin Reverb tone immediately returned! When doing the cap job, I decided to run all the bypass caps through my cap tester and here’s what I noted: The new 22uF 50V IC caps all measure 25.85uF with an ESR of 2 ohms (pretty much consistently) The old 25uF 25V Mallory (white) caps measure 32uF with an ESR of 2.8 ohms to 43uF ESR 3 ohms (each one different). Ran the Amp Books cathode bypass calculator and ran the numbers, nothing startling showed-up, can't account for the "black-art" going on here, but left the old white caps in and I'm happy with my amp.

Hey, loved the video and Rusty didn't do too bad himself.......I also caught the trailing value that persuaded me to go ahead with what I was considering, and yes, it gave the desired blues sound I was after.......Thank you

Uncle Doug, I appreciate greatly your videos as all of them are intelligent and genuine as well as hilarious at times..when you explain, we understand. I have builds many tube amps thanks to you. we want more of your superb videos..(Y) thanks loads..

Thank you! Helped me on bias switch mode I'm doing now

Can't thank you enough.

There is a signal inversion from control grid input to plate output. The sine at the plate should be inverted! Good job, however, I do enjoy your videos. Happy 100!