How to read guitar amplifier schematics

[@howardthegasman]

When a newcomer to all this, this is exactly the content you need. Very instructional and thank you Stuart

[@stuartukguitarampguy5830]

Thanks Howard

[@delatronics3257]

Thanks for sharing, I am also a service engineer was based in Harrow, then Milton Keynes, worked for Roland, Yamaha Line 6 and Alesis (mostly digital with some transistor circuits, since relocating to Brazil, I am called to repair guitar valve amps and authorised by Marshall, Fender, Bugera etc. I only have just over 35 years of experience but not a huge amount on valves. Thanks to your channel and Uncle Dougs, I have refined my knowledge and also learnt about substitution of tubes and their characteristics (ie. EL34, 6L6, 6V6..). You'll be glad to know I already knew 99% of what you said, but it's good to be reminded and I wasn't too sure on how the negative bias was derived. Unfortunately many amps don't have a bias pot, so you need to calculate the relevant resistors.

[@stuartukguitarampguy5830]

Great to hear from you and thanks for shating. I went to Recife once!

[@mariofabrizi5050]

As a guitar player I really enjoy you walking us through these amps

[@stuartukguitarampguy5830]

Thanks Mario!

[@stevemitchell9848]

​@stuartukguitarampguy5830 wow...your so smart...and the way you explain is so good..

[@michaelevans3852]

Thank you so much! I will watch this many times I'm sure. I'm amazed at how much this opens my understanding and brings new questions at the same time.

[@stuartukguitarampguy5830]

Thanks Michael I'm pleased you found it useful.

[@miguelrichartmellado2834]

Very very good video. Thank you Master.

[@stuartukguitarampguy5830]

Thanks Miguel.

[@StephenEgertonMusic]

This was great, and even having watched a great many “basics” videos, you clarified several points for me. Thank you!

[@stuartukguitarampguy5830]

Excellent thanks Stephen

[@braaijmakers]

Hi Stuart I also have a schematic of a Preamp by Langner. It is a bit complicated. Maybe you can check it out.

[@PhuketMyMac]

Really useful. Thank you!

[@goodun2974]

A useful automotive-themed mnemonic device for understanding the symbols for resistors and capacitors is that a resistor is like a series of speed bumps for forcing traffic (voltage and current, ie: electrons) to slow down and lose energy; and a capacitor is like an automated tollbooth gate mechanism that needs to be charged up (a handful of coins thrown in the basket) before it can let the current pass through.

[@stuartukguitarampguy5830]

Nice thanks.

[@Ten2More]

Thanks! You explain it well!

[@electrolytics]

Fan-Flippin'-tastic! Solid Value in this video. I did pick up a little bit more with your video and I got reinforcement on what I learned before but maybe kind of forgot. Thank you Mr. Stuart. Much obliged.

[@stuartukguitarampguy5830]

Excellent!

[@decleafs4]

Thank you VERY much! Very informative...to me anyway. I'm a rookie. Subscribed.

[@stuartukguitarampguy5830]

Great I'm so pleased.

[@Kate_Short-For-Bob]

Excellent. As a mechanical engineer (!) But some (30 year old) electrical training, this is really interesting to understand whats happening in my valve amp. 1 question - whats the purpose of the 220k resistor after the pre-amp stage (after the coupling capacitor) ? In my simplistic head, doesn't that just lose some of the hard-earned increase in power just made in the pre-amp ?

[@stuartukguitarampguy5830]

Hi those 2 x 220K resistors are where the bias voltage is fed in. They are very high value resistors and so the loss is very small.

[@cuinoz3569]

Excellent presentation Stuart. Really enjoy your videos. Would be a blast hanging out with you in your shop for a few days. Thanks for sharing your knowledge. Looking forward to watching some more of your videos.

[@stuartukguitarampguy5830]

Thanks I'm pleased you enjoyed it! Feel free to drop in if you are down my way (Reading)

[@davidthomas1356]

I really enjoy your videos. I am an "automotive technician," so I get the diagnostic process. Have you made a video of th ahop, or more specifically, your special and not so special tools? I have been able to pick up on a few watching your videos. Thanks for doing what you do . P.S. im especially interested in your magnified and lighted work glasses.

[@stuartukguitarampguy5830]

Hi David I'm pleased you are enjoying the vids! No I haven;t made any vids on the tools I use apart from the variac setup I have.

[@camielkotte]

I am building up courage and confidence to "repair" my super twin reverb" also i have a twin reverb with several known issues . In my search in the last year this video is the most valuable in understanding how amps work. Thank you a bucket of tone for your generosity in educating people! Cheers!🎉

[@stuartukguitarampguy5830]

Thanks and good luck fixing it.

[@FenderStratWannaBe]

Thank you for the spot on amount of information here. I matched the rest of the schematic to the components .. I think 🙂. The 3 CAPS in the POWER amp, and the 2 series caps of the Power supply are in the "doghouse", is this correct? By showing us the Vibrato Preamp section, it was easy to deduce the pre-amp for Normal and Reverb (on a SuperReverb). Awesome, thanks again!

[@stuartukguitarampguy5830]

Yes that's correct. Glad you enjoyed it!

[@tom1263]

Very cool. Trying to follow along on my Marshall JMO schematic. Fender definitely is easier to follow.

[@stuartukguitarampguy5830]

Great that's how you learn!

[@MiniShowProductions]

I’m currently building a deluxe reverb with this AB763 circuit i have absolutely no idea about any of it but it was brilliant to learn a little and i am sure i will come back agin and again until it all syncs in properly so thank you very much indeed

[@stuartukguitarampguy5830]

Great I'm pleased it was useful and good luck with the project!

[@dangoldbach6570]

On the high tension rectifier, are there three diodes stacked in series to allow for a lower voltage rated diode to be used to withstand the 440V B+? ( Im thinking along the lines of three 250v diodes could withstand 750v in series...)

[@stuartukguitarampguy5830]

Hi Dan Yes I believe that is why they do it.

[@dirtybird850]

Can you explain what B+1,B+2,B+n stands for? Thanks for the excellent lesson!

[@stuartukguitarampguy5830]

They're just old deginations from way back when. Mught as well call the A, B and C for want of anything better. They are DC voltages.

[@Ritchie1954]

hi Stuart.. Thanks for the basics very much appreciated Top man ..

[@stuartukguitarampguy5830]

I'm pleased you enjoyed it.

[@tomfoolery2082]

I worked in civil engineering for 30yrs I'm hoping this will be similar enough tht it will be a smooth transition. I'll see soon enough . Thks

[@stuartukguitarampguy5830]

Let's hope so!

[@michaelevans3852]

Stuart, I completed my first cap job on my Fender Concert today. I also replaced several resistors that were out of spec. I plugged it in with my variac and bulb set up. It no longer blows fuses, but I found the vibrato channel was still weak. I couldn't figure this out until I pulled the tube and one of the connectors came off on the tube. It must have been broken. I will replace this socket and see if that clears it up. It is your videos that Gave me confidence to do this and the ability to do it in a safe manner. The video on schematics has helped me greatly in understanding how tube amps work. I'll continue watching and learning while exercising my skills. Thank you so much for your continued tutoring. Mike.

[@stuartukguitarampguy5830]

Excellent well done Michael.

[@kitwarren2493]

Thank you very much for this! Learnt so much from you already and excited to get stuck into some less beginner friendly content soon!

[@stuartukguitarampguy5830]

Excellent thanks Kit

[@jamescox1815]

Thanks for the great tutorial. You have a real gift for making all the seemingly complicated very easy to understand for the novice, without unnecessary waffle or condescension. It's much appreciated. I've subscribed and I look forward to diving into more of your videos. I'd really love if you could do the same breakdown with some guitar pedals. Cheers.

[@stuartukguitarampguy5830]

Thanks James. Hmm, guitar pedals are SO varied and often fiendishly complicated. They even have 100 pin computer chips and suchlike in them!

[@tomasfuchs4277]

Absolutely fantastic video, thank you so so much!

[@stuartukguitarampguy5830]

Thanks Tomas!

[@lousekoya1803]

It's me again ! hihi ! I'm a house builder and so frustrated that I didn't choose electronics when I was youger at school . Trying to understand and re-visiting this video and I must say that the way you explain things is really good so thanks for the second time ! Will watch them all and like them all !

[@stuartukguitarampguy5830]

Hi lou. I'm an electronics engineer and so frustrated I didn't become a builder5 - would have been minted by now!! :) I'm glad you're enjoyong the vids. Keep learning!

[@lousekoya1803]

@@stuartukguitarampguy5830 Haha ! That is funny ! I love the vids ! Take care !

[@JONNIE_ROCKER]

Thanx for sharing

[@dumbbanshee5799]

Found this really useful! I would find another walk through like this with a class A solid state amp really helpful as well. The way you explained everything was at the perfect level of specificity.

[@stuartukguitarampguy5830]

Thanks for the great feedback I'm glad you enjoyed the vid.

[@BR-kj3fp]

Thank you so much for taking the time to explain this.

[@stuartukguitarampguy5830]

I'm pleased you liked it.

[@PurposefulPorpoise]

Would love to see you go through each half of the 12ax7's and what they do, cathode follower vs driver stage vs phase inverter(long tail vs cathodyne) ect. Thank you

[@lousekoya1803]

Oh man , how come this one slipped ! So happy ! Thank you Sir !!

[@stuartukguitarampguy5830]

Glad you enjoyed it!

[@silasfatchett7380]

36:41 The choke and the first 20u/525V capacitor form an LC filter, applying a stage of smoothing to the DC supply to the screen.

[@curtiseverett1671]

how come every time I drink too much beer, I get shocked?

[@stuartukguitarampguy5830]

Ho ho!

[@johnc.4625]

What a brilliant video. Thank you!

[@stuartukguitarampguy5830]

Thanks John

[@2222222aaa]

Thank you

[@user-sh9du2nv5y]

Well done 👍

[@Bob-1802]

I had a home-made amplifier in the 70's using a single 12AX7 in class-A ouput stage. It was good enough for me.

[@stuartukguitarampguy5830]

Ooo, nice, About half a watt then!

[@Bob-1802]

@@stuartukguitarampguy5830 Probably closer to 100mW. Nevertheless with a good sensitive speaker and a decent enclosure it was loud enough to make my neighbors angry 🙂😠

[@ertreri]

In this video, the guitar input circuit looks interesting. The input signal seems to be going through resistors to the preamp grid, but there's also a path for both inputs 1 and 2 that appears to be grounded. Is this intentional, or are the ground wires supposed to connect to the jack's ground lug instead of the hot connection? it is hard to imagine a short to ground from the hot would make any sense. thanks

[@stuartukguitarampguy5830]

I think what you're seeing is the fact that when the guitar lead is UNPLUGGED, the hot contact is grounded. This is to stop the amp humming. When you plug in, this ground connection is broken.

[@ertreri]

@@stuartukguitarampguy5830 Thanks, that was most definitely not obvious. While a direct short to ground on the hot input during normal operation wouldn't necessarily damage the circuit, it's not a typical design choice for a couple of reasons: 1. **Potential for Ground Loops:** Even though the hot isn't connected to a power source until the guitar cable is plugged in, a direct short to ground on the input could create a ground loop if there are other grounding inconsistencies in the circuit. Ground loops can introduce unwanted hum or noise. 2. **Unexpected Behavior During Troubleshooting:** If a technician were troubleshooting the amp without a guitar plugged in, a direct short to ground on the hot could lead to unexpected behavior, making it more difficult to diagnose the actual problem. In a well-designed amp, grounding the sleeve of the input jack is the preferred method to minimize noise when no cable is plugged in. This avoids potential ground loops and unexpected behavior during troubleshooting. Would you agree?

[@ertreri]

Fantastic video. Thanks so much. It would be cool if you could explain in the input jack the low impedance and the high impedance inputs. Also, when we see connections to ground, is it really the amp ground or is the ground connected to the Neutral power supply cable?

[@stuartukguitarampguy5830]

Glad you enjoyed it. Yes the ground is the metal chassis and that's connected to the eartn wire in the plug, definitelty not neutral!

[@ertreri]

@@stuartukguitarampguy5830 Hi, thanks for your reply. Is it normal to have circuit that just dumps a massive amount of current to the ground as part of normal operation? The giant smoothing capacitors with the 400 volts rating in series, are acting like some sort of high pass filter right? The AC signal starts becoming like DC to feed the voltage of the power tubes but the high frequencies are constantly sent to ground. I suppose this is normal, but still somewhat surprising as sending signal to ground is normally we intuitively see happening as a safety mechanism when something shorts and connects a voltage source to the metal casing. Still too much of a ignorant in respect to electrical circuits, it's what it is.

[@stuartukguitarampguy5830]

@@ertreriHi It's a bit hard to explain in short reply. Maybe the mest way is to consider a battery connect to a lamp. So the positive goes to one side of the lamp and the negative to another. The amp lights. WHere is the current from the positive terminal (which goes through the lamp) being 'dumped' to? It's dumped to the negative side of the battery, right? Now if I happen to also want to connect that negative terminal to my metal case and also the mains ground, nothing changes. No current is being 'dumped' to ground in that case. It's the same with mains powered gear. That's the best I can do without a coirse in electrics! Keep studying and learning.

[@AudioStorm1980]

Man you are awesome....I subbed.

[@stuartukguitarampguy5830]

cheers Josh!

[@ronnocm8633]

Hello, great vid, I am looking for the best place to get a schematic for Peavey valveking 112 version one, that shows the valve positions V1, 2 and 3 so I can experiment/try different pre amp tubes, any pointers would be appreciated.

[@stuartukguitarampguy5830]

V1,2,3 are all 12AX7 (ECC83). LEave V3, that's the one nearest the power tubes and is the phase inverter. V1 is nearest the input jack. There's not a lot you can experiment with really. You won't hear any difference between valve makes. All you can do is reduce the gain but putting a 12AY7 in the V1 position. What are you trying to achieve?

[@ronnocm8633]

@@stuartukguitarampguy5830 Thanks very much for replying Stuart, I was after exactly what you said, I have a HRDLX I got an amp tech to swop out the original Caps, I put a ecc81/12AT7 in V1 and changed the speaker for a TREX and bingo, sounds great i'm into SRV. I can find schematics for the fender but nothing decent for the valveking, so I wanted to know which was V1, you answered that and I am very greatfull, what do you think of the 12AT7 in V1 on the Peavey ?

[@stuartukguitarampguy5830]

@@ronnocm8633 I have the schematic for the VK if you want it. At the end of any video you'll see an end graphic with my email on it, contact me via that. I prefer an 12AY7 to the ECC81 if it's a gain reduction you are looking for.

[@ronnocm8633]

@@stuartukguitarampguy5830 Theres a website cant see an email

[@Roy-xe9is]

thank you so much for this!

[@stuartukguitarampguy5830]

Glad you enjoyed it Roy.

[@jimcastillo8950]

Hello Stuart, great tutorial.... I changed my normal circuit on my Vibrolux reverb amp. I changed the .047uf coupling capcitor to a .033uf and changed the tone stack bass .047 uf cap to a .022uf like the super reverbs. I now enjoy the normal channel. It seems more open and not muddy . Very useful.

[@stuartukguitarampguy5830]

Ok interesting thanks.

[@Tanax13]

Really great explanation! Would you be willing to make a video how guitar schematics map to the actual circuit boards? That's what I conceptually don't understand because the board obviously looks nothing like the schematics, even though it follows it (I guess) :D

[@stuartukguitarampguy5830]

Hi. The problem with that is that it varies from amp to amp, there is no standard tranlation. It's not usually too difficult to follow though. E.g. find V1, then find pin 2, ah... there's the 100k resistor which is on the schematic etc. The layout is usually fairly logical.

[@TheAustinGuy]

You’re the best!!🙏🏼

[@stuartukguitarampguy5830]

Thanks Jason.

[@edwardhannigan6324]

Hey Stuart, just a fab video..Lots learned again...This explanation of the circuit certainly does remove some of the fog I have with regard to the schematic and it's reading. Thanks again for posting, keep em' coming..Ed..UK..😁

[@stuartukguitarampguy5830]

Thanks Ed

[@ssiowi]

Excellent primer; thank-you. Looking forward to more. Topics of interest: a) amp biasing demonstration, b) Class D amp schematic primer. Thanks again!

[@stuartukguitarampguy5830]

Thanks David. I wonlt be doing the class D primer - barely understand it myself!

[@gbtcstl]

I've had been interested pretty recently into electronics, specifically for amp construction and studying more deeply a Mesa/Boogie Mark IIC+ schematic. Stuart, I can't thank you enough for this video as it's shedding a light on what it seemed like pretty much rocket science so far as a newcomer 😂

[@stuartukguitarampguy5830]

Great I'm pleased you liked it.

[@brendanwalsh108]

Hi Stuart. I've owned a few amps over the years (from a 200w Marshall stack back in the 70's to a Vox 2w [two w] Night Train now!) but never really understood what goes on under the bonnet. Your videos are fascinating and very easy to understand because of your style of presentation. Thank you.

[@stuartukguitarampguy5830]

Thanks Brendan

[@starscream007]

Hi Mr. Stuart, your beginner tutorials are amazing. I have learned more about electronics and power circuits from your 3 videos about how tube amplifiers work than in all the hours of classes in school and university. I am a bit ashamed to say it frankly, but the truth is that mechanical engineer degrees in my country don’t go very deep into electro-engineering. Is there a possiblity that you make similar videos for transistor amplifiers like the ones you made for tube amplifiers? Cheers.

[@stuartukguitarampguy5830]

Thanks very much! It's the same for me. My degree in electrical engineering didn;t really do much on the mechanical side. Yes that's a good idea, I'll do one on transistor schematics.

[@Jonobueno]

Thanks mate, that was really informative and well explained. I built a couple of 5E3 Fender Deluxe clones that wen really well and enjoyed the build. It's good to have an understanding of how things work. Cheers !!

[@stuartukguitarampguy5830]

Great well done Adam

[@icchinn4971]

Hello Stuart, I'm a Japanese guy who builds his own guitar amps as a hobby. I found it helpful to remove the thin wire coating inside the reverb tank by melting it with the tip of a soldering iron. I don't want to put tension on the thin lines, so I'll try it next time.

[@stuartukguitarampguy5830]

Yes that's the best method.

[@cpchris2]

Awesome explanation.. iv done an electronics degree but never did valve amps .. loved this thanks

[@stuartukguitarampguy5830]

Thanks Peter.

[@raedwulfone]

Very well done cleared up a lot of questions ....I have worked on my own and some friends' amps for years and schematics are a weak point. I have been doing a deep dive on them for a few months now and this was very helpful. Thanks and Regards

[@stuartukguitarampguy5830]

Great I'm glad it was helpful!

[@GiulioLuzzardi-xf1xo]

I watch and listen to this before any DIY on my amplifiers, it helps keep my mind clear of clutter and gives me a bit of "Why" these components work, thankyou.

[@stuartukguitarampguy5830]

Thanks Giulio I'm glad you find it useful.

[@old2begin]

Really useful video - thanks for sharing your extensive knowledge.

[@stuartukguitarampguy5830]

Thanks Greg

[@ronniemonday]

Thank you for taking the time too share the knowledge , my kind of entertainment for sure. From across the pond ,thumbs up!

[@stuartukguitarampguy5830]

Cheers Ronnie

[@ThirteenToOne]

can you do one for the triple X....

[@stuartukguitarampguy5830]

Hi Jay What is the triple x?

[@ThirteenToOne]

@@stuartukguitarampguy5830 peavey amp.. my first real badass amp I got around 2001 and it just died... dont know why... not places around me that fixes them... had a guy looking at it... he does some stuff with amps... its got him stumped... I have another one, but thats my baby...

[@thomasmogensen1]

Keep up the great work 👍🏻👌🏻

[@mickel7b]

Thank you so much for all your videos Stuart! You have really helped me learn a lot. Your channel is worth its weight good (and I'd venture your channel has featured quite a few ac30s, so that's a lot!)

[@stuartukguitarampguy5830]

Thanks I'm really pleased you enjoy it!

[@shredx81]

Amazingly informative again Stuart! Thanks!

[@stuartukguitarampguy5830]

Thanks! Glad you enjoyed it.

[@circlemover]

As a novice - this is explanation has been invaluable. Thank you for taking the time to do this. Areal gentleman and scholar.

[@stuartukguitarampguy5830]

Thanks very much.

[@pda49184]

Great video Stuart especially showing the part of the amp's actual circuit relating to the schematic. It certainly helps if you can read resistor values which helps you identify from the diagram which part of the amps circuit your looking at or trying to identify.

[@stuartukguitarampguy5830]

Cheers Pete

[@divebomb99]

Stuart, you rock more than all the amps you've ever serviced combined. Thank you for taking the time to make this video.

[@stuartukguitarampguy5830]

You're too kind!

[@nune8074]

Very informative video. Thanks.

[@stuartukguitarampguy5830]

I'm pleased you enjoyed it.

[@sensor-sweep]

you have no idea how helpful this was. thanks!!

[@stuartukguitarampguy5830]

Thank you so much!

[@rgbplumbinghilton]

Very informative for beginners. It's nice that you take your time to teach here 👏

[@stuartukguitarampguy5830]

Thanks Richard

[@MichaelSmith-rn1qw]

Good presentation Stuart! If you want to give yourself a headache, track down a schematic for a Fender Super Twin Reverb amp. They were only produced from about 1976 thru 1980 or so. 180Watts RMS, 395 Watts Peak. Six 6L6CG power tubes, and a couple of unusual tubes in the circuit. (6C10 and 6CX8). If you want to see photos of the inside of mine, let me know.

[@stuartukguitarampguy5830]

Hi Michael I have that schematic do you need it?

[@miguelrichartmellado2834]

That amp is a monster. In my city there are two, 2x12" combo.

[@MichaelSmith-rn1qw]

@@stuartukguitarampguy5830 Hello Stuart. I have that schematic. I actually printed it out on four letter sized pieces of paper and taped them together. I showed "Uncle Doug" how to set up the printer to accomplish that. It comes in handy for complicated schematics where you want a hard copy to make notes on.

[@MichaelSmith-rn1qw]

@@miguelrichartmellado2834 Yes, 2 x 12 combo. Mine has the UTAH speakers with the large square magnets. Very heavy. I built a head cabinet for the chassis, and left the speakers in the original cabinet so it's easier to transport.

[@stuartukguitarampguy5830]

@@MichaelSmith-rn1qw Ok great. I usually just print off the bit I'm interested in. Tbh I rarely have to do even that.

[@miguelrichartmellado2834]

👍👍

[@tagacale1733]

thank you!

[@stuartukguitarampguy5830]

Glad you enjoyed it.