VALVE/TUBE Amp Circuits EXPLAINED! | Too Afraid To Ask

[@ScienceofLoud]

Valve amplifiers are still the most desirable sound in guitar music despite the vacuum tube being made obsolete by transistors in the 60s. What is going on inside to make them still sound so good all these years later? We analyse the circuit of the Orange AD30 to find out more. Get your AD30 - Thomann - www.thomann.de/gb/orange_ad30htc_gitarrentopteil.htm?offid=1&affid=367 Sweetwater - imp.i114863.net/WZN7M Reverb - reverb.grsm.io/orangead30 AD30 Gain Appreciation: kzbin.info/www/bejne/pmLXl3VjfaeXmcU This video contains paid promotion from Orange Amplification #valveamp #tubeamp #orange More from CSGuitars: Gain access to exclusive content at: www.patreon.com/csguitars Join CSGuitars Discord - discord.gg/d7b6MY8 Buy CSGuitars Merchandise - www.csguitars.co.uk/store Website - www.csguitars.co.uk Contact - [e-mail]

[@doctorscoot]

in my memory, if it has push pull then it's class AB. a strict class A would have a single amplifier stage (one output valve) and then removal of the DC bias via the output transformer

[@ScienceofLoud]

Class A push pull is also possible as described in this video. What you are thinking of is Single Ended operation which can only be Class A

[@doctorscoot]

@@ScienceofLoud ahh yes ok. I was taught in a naval workshop but it was goddamn years ago now - thanks ;)

[@davidfuller581]

I think it would have been prudent to mention that a gain stage with grid input and plate output has an inverted output polarity compared to the input, which is part of how the phase inverter/phase splitter works. (This amp's phase inverter is a kind of circuit is called a Long Tail Pair or Williamson inverter, but I'm sure you know that). Otherwise kudos on a good basics video.

[@okayestguitar66]

Your simplified description of class A vs AB is, in my opinion, one of the best and easiest to understand. Thanks for that. On a side note, do you record to tape? Or was that just for show?

[@achannel1818]

Mad respect for teaching some real engineering here.

[@mihailmilev9909]

90th like

[@steveg.3022]

I learned this in electronic tech school back in the ‘70s. Great to see this here.

[@johnegginton]

Possibly the best PSA I've ever heard! "I'm not responsible for any electric shocks, injuries or deaths that result from the stupidity of you ignoring this warning" 😂 On another note, brilliant explanations! This kind of thing is something I really enjoy learning. I've been building pedals for a bit now and have a background in electrical and electronic engineering. I don't have any valve amps to tinker with though so I'll not die just yet 😂

[@mihailmilev9909]

Same! Ikr lol. Loved that

[@Geopholus]

i've been tinkering with tube based amps for almost 60 years since before age 12, with the amount of caution that a reasonably mature 12 year old can muster. Though I appreciate the warning, one can go too far with such things, and not describe how to be careful (which one should) in such a video), and not encourage people to try things at home,... no one really learns anything except through experience.

[@hazrod13]

One more perfect TATA video that I'll be re watching many times !

[@Tehstroyer]

Me too. Maybe I'll even understand it one of these times.

[@armax00]

with all these diagrams and wonderful explanations, I am still waiting hopefully to purchase some day the guitar related electronics course :)

[@ScienceofLoud]

If I ever take a break from weekly videos here on YT then I'll have the time to make it happen.

[@mihailmilev9909]

Lol

[@mihailmilev9909]

Lul

[@PJ-hn4cg]

Ha ! Yep !

[@glassappreciation8883]

Such an underrated series, couldn’t ask for more.

[@attilacsaba]

its not like im going to go and build an amp but this was interesting and good to know ... thanx

[@ikestoddard2458]

Colin, this is a marvelous explanation. I am an electrical engineer but just into the transistor era of training. I think you covered it well. Thanks!

[@Ten80pete]

Can confirm that the old tube electronics pack a hell of a punch. I only wish my Dad or brother had given me this warning when they were fixing an old floorstanding radio model when I was 5. It was off and unplugged, but don't expect a little kid to NOT touch something that has that warm glow.

[@Alex-tm4th]

Showed my 8 year old my old 90s 5150. He said it was loud and asked what the volume was at. I told him zero and his jaw dropped. Lol

[@hankgesmag9650]

From one scientist (MSEE) to another (Colin): Nice presentation! Probably one of the best on KZbin...

[@jcool0122]

I build amps as a hobby and I have to say that is a very clear and concise explanation. Can you do that with the switching section of a Boogie?

[@jcool0122]

@@dr.know-it-all5148 actually, Brad the Guitalogist is the only person I've seen on KZbin take on a Boogie.

[@knowmusicman157]

@@jcool0122 he's qualified

[@castleanthrax1833]

@@knowmusicman157 He's also nuts. ✌️🇦🇺

[@yoshi-808]

That was a two-sentence masterclass in impedence matching!

[@Jesterhead21]

This channel is pure gold. Thanks a lot mate!

[@jamessilver2748]

Brilliant vid, I learned a lot there Colin. The "too afraid to ask" series has been inspired.

[@dougstewart6581]

I love this channel sooooo much instantly. It has science, sound, a Scottish accent and you just described a sound as a “saggy bottom”. Love it. Thanks dude

[@grberendzenproductions312]

Very thorough! I wanted to watch just to see how well you'd explain things. (Plus, I like it when you say "zed") I'm impressed! You went through phase splitting and impedance matching as well. The only thing you didn't do was explain how to drain a capacitor so you could safely handle it, but you weren't teaching how to work on an amp, just how they work. And you let us know never to turn on a tube (or valve) amp without a load. Well done!

[@castleanthrax1833]

When I bought my first valve amp (many) years ago, pre-internet, I didn't know anything about them but I kinda guessed the importance of attaching a speaker, going by the bright red indicators around their input jack sockets. ✌️🇦🇺

[@silasfatchett7380]

Turning on a tube amp with no load is not a problem. Attempting to amplify a signal with no load causes damage.

[@kevinhernandez2594]

Therapist: Southern Colin isn't real and cannot hurt you. Southern Colin: 18:03

[@WwYnN]

I like your explanations. Not boring, not over complicated. Well done sir.

[@johnrodgelatenemusic7262]

This has to be one of the very best explanations of how valve amps work that I’ve seen in over fifty years of working with the damn things! Loving your channel Colin.

[@vincentl.9469]

All well & good but will this stop valve amps ending up on the scrap heap?

[@johnrodgelatenemusic7262]

@@vincentl.9469 mine certainly won’t. But I’ve got a few spare sets of valves which will see me out. Long term I don’t know, maybe you’re right.

[@admnovsk88]

This brings me back to analog circuit class back in college in 2006, thank you

[@parkerdavidson5868]

Working on my amp like a cheap dum dum instead of taking it to a repair technician. I did once before and it actually worked out, but my job was minimal and just enough to keep the amp running, so I'm gonna go back in soon and redo it properly. I'm on a kick of researching more how amplifiers work, and how to safely work on them, and it's an absolute win that the example you have today is my amp! Thanks for this video!

[@ChrisBlackLabel90]

Just watched this after a 12 hour shift; my brain hurts now. Thanks Colin.

[@StratsRUs]

Your perfect presentation and pacing takes you beyond just the guitar world.You make a great teacher that expresses themselves because you are a musician too.Amazing work.Thank you.

[@Paul_Lenard_Ewing]

Excellent, Excellent, Excellent!!!! I would love to see a series of shows breaking it down into smaller chunks so you can use more layman's terms in your description. Things like what's a diode need clarity. It is like explaining how a house is built and using the words brick and bricks when one does not know what a brick is. This does give one a good overview in a short time so it serves it's purpose. In short one gets the big picture here. For example I like to start with the A/B thing with the idea it is a bit like a old fashion hand pump to pull up water from the ground.

[@Yupppi]

This is the good basics stuff that is still difficult to find unless you browse through forums and it's almost never as coherently explained. Even the literature is a bit here and there and not necessarily available anymore. Very good episode. Does the single half of a triode invert the signal btw? In the graphics it was still in the same phase, but how does the blocking of the grid actually affect the electron flow? Does it depend on other features if the valve inverts the phase? I also sometimes see techs preferring to bias for slight crossover distortion, which to me is very interesting when many times you see people talk about crossover distortion as something you absolutely don't want. I understand that most of the time if the amp is rated much above 5 W, you can be almost sure it's class A/B instead of A, that it would become so costly to amplify with more power in A. Any thoughts on the common ranges of class A? And like you said, probably the first part of the amplification is in A often times.

[@MagyHimself]

Yes, the triode inverts the signal (when its provided through the grid), if taken from the anode. When taken from the cathode, it keeps the original phase.

[@Geopholus]

Yes, the signal is inverted relative to the input control grid signal, by a common plate circuit, in which the output is taken at the plate resistor ( higher value or equal to the cathode resistor ). Magy Himself, is correct,.. although in the case of the phase inverter, the bottom half of the circuit , which is called a "differential pair", produces a non inverted output signal relative to the top signal grid because it's grid is referred to ground, but the sum of the two currents at the cathodes (where they join together is a point of unity (no signal)), so the grid of the lower part of the differential pair receives a degenerative feedback signal at it's grid which, is out of phase with the signal applied to the top grid. I know that sounds confusing, but that is how it works. The bottom half of the circuit receives a "virtual" signal at it's grid because the two currents sum together to equal a constant current, at the cathodes.

[@silasfatchett7380]

The varying current (electron flow) flows in a plate resistor to the positive supply. At idl

[@silasfatchett7380]

Sorry, changed my mind. I remembered that I posted an explanation elsewhere in these comments, then hit the wrong button.

[@emmettyoung7603]

i don’t play metal, but i love your channel a ton. it’s useful for everyone who’s interested in music or audio.

[@KRAZEEIZATION]

I’ve been using tube amps since 1994 and nothing else can match the sound and touch sensitivity. Now I’ve 6 tube amps amps and have no issues with owning many more!

[@bigboidadcoq]

This is a goldmine of a channel. Thanks Mate !

[@williambock1821]

That was the best explanation of what true class A vs AB are I’ve heard yet! Very nice! It DOES get confusing when you see amps calling themselves class A that have more than one output tube. If you REALLY want some sag, stick a 5y3 in there! A GZ34 is extremely close to SS diode performance.

[@justincary1599]

Such well presented, accurate information. Subscribed!

[@Forest0922]

Super good video, really appreciate it. Also in North America it's actually 120v. There is a standard called ANSI C84.1 that effectively says we allow +/-5%, meaning 120v is the target but anywhere between 114-126v is okay. Also it's 120v because we are splitting a single phase of 240v in half.

[@mingram008]

Excellent job explaining the sections of the amp! It was very easy to follow AND made sense! Keep these videos coming and we DO appreciate the work you put into them! Will be following.

[@Okla_Soft]

I’ve been watching some real in-depth videos over the last year or so about how tube amps and transistor amps work, and it’s so cool to see this channel go so in-depth on the circuitry. Apparently Colin has some engineering knowledge.

[@paulzytsel3557]

WELL DONE - FROM A TECH WITH OVER 40 YEARS EXPERIENCE.

[@richardmawdsley2589]

Great explanation, thankyou. I still use my Fender Bassman 135 silver face for regular gigging on bass!

[@abirbhabsengupta0007]

Can we use the modern electronics with the same specifications in this amp circuit

[@Mikey__R]

A fun way to find out if a valve output stage is actually push pull Class A, is if the shared cathode resistor is missing its bypass cap. In a true Class A amp, the current signals through each valve will cancel, so you'll get no AC component superimposed on the DC bias voltage, so the amp would be unable to operate in Class B. If you do have bypass caps, which are necessary if you dont have shared cathode resistors, then it /might/ be Class A at all output levels, but it'll probably start to push it's way into Class B as the stage begins to saturate. You're right, it's all marketing, and TBH I think most people think Class A means cathode biased EL84s, no matter what the actual class of the amp really is. Final point: cathode based amps actually have worse crossover distortion the deeper into Class B they go. It's not a bad thing, it's part of the sound and bloom of the amp.

[@rotaxtwin]

Brilliant, your addendum to go into detail on Class A, B AB was very good.

[@Spivonious]

Fantastic! This really helped me understand the schematic for my Genz Benz El Diablo 60 and identify the various pieces of the circuit.

[@emptyMan0]

Thanks for the video, Colin, it has cleared some of the mysteries, but some still remain. Could you possibly elaborate in a future video on some of these topics? - If I have a multistage preamp, does the gain knob actually turn multiple potentiometers, one for each stage? - What is a valve bias? - How can a valve amplify in the negative portion of the wave if it only allows current to flow in one direction?

[@silasfatchett7380]

In an amp with an input stage followed by two gain stages, a single gain control is positioned before the 1st gain stage, controlling the amount of signal which goes to the 1st stage from the input stage. As the gain control is advanced from zero, at first both gain stages amplify cleanly, then as it is advanced further, the amplified output from the 1st stage overdrives the 2nd stage clipping the signal resulting in distortion. Eventually, the increased input from the input stage to the 1st stage overdrives the 1st tube adding more distortion. At maximum gain, both tubes are heavily overdriven for maximum distortion. When no signal at the grid, there is a current flowing in the tube, so that a positive going signal on the grid can increase the flow, while a negative going signal can decrease the flow. To accomplish this, with no signal at the grid it must be at a negative voltage with respect to the cathode which is known as 'negative bias' 'Biasing' is the process of determining the negative bias voltage during the design of the amp. It can also mean adjusting the negative bias on output tubes, which in turn, controls plate dissipation.

[@emptyMan0]

@@silasfatchett7380 Thank you very much! The gain control now makes sense to me. I am still not sure I understand the bias thing. Does it mean that the amp is set in such a way that the plate is the input voltage plus a constant voltage roughly in the middle between the cathode and anode and that is then somehow subtracted before it hits the speaker?

[@silasfatchett7380]

@@emptyMan0 At idle, the plate current in the tube flows from the plate through the plate resistor to the positive supply, so according to Ohm’s Law there must be a voltage dropped across it. This means that the supply voltage is shared between the tube and the resistor. The negative bias voltage is set so that the plate voltage at idle is at around 2/3 of the supply voltage. A signal on the grid varies the plate current which varies the voltage across the resistor so that the plate voltage varies in sympathy with the grid voltage, resulting in a much larger (and inverted) copy of the grid signal at the plate. This varying voltage is fed to a coupling capacitor which blocks the DC idle voltage but allows the AC signal to go to the next stage.

[@emptyMan0]

@@silasfatchett7380 Thank you again, I think I get it now.

[@DesertRat332]

Explained so well, even an old mechanical engineer can understand it! 😄 I'm still glad I didn't go into electrical engineering, because that stuff is a magical black art!

[@beaarthurmiller]

Discord notification squad!

[@hazrod13]

Squaddddd

[@ScienceofLoud]

SQUAD!!

[@dc4019]

SQUAD

[@kirkbolas4985]

Le squad

[@NashTheGreat]

Сквад!

[@jessebreakspear6656]

That was awesome! now I understand the class A vs class AB concept so much better. I still don't fully understand how the myth of the Vox AC30 being class A got started but that would be more of a history lesson right?

[@effsixteenblock50]

I'm not sure but perhaps AC30s are biased in such as way as to spend most of their time in class A. They certainly sound more class A than your typical Fender or Marshall amp.

[@nairanvac79]

Thumbs up for the Laphroaig 👍

[@dc4019]

I absolutely adored this video! Thank you!

[@johnterpack3940]

Okay, the post-credit bit got me. Howdy from Texas.

[@matiaslopezvarela926]

Love that laphroaig 10 next to you. Valvs and Single malt 🙌🏻

[@AlbusBand]

Well said my dude….I love the science behind why things work the way they do; even if I have to re-watch to digest it all. You sir, are second to none. Hope you’re well.

[@ronniemoysey8854]

Brilliantly delivered warning. And fair. Out of curiosity, how many deaths / shocks did this video generate?

[@BrandochGarage]

Love your channel. Took me 50 years to figure out what high tension meant. And I learned it from a guitar Channel. You gotta have the valves if you want to be haired. Peace.

[@OsLapsosBandaRock]

Valve Amps are the electric guitar best friends!🤘🤩 Great video, by the way!

[@altemose_prime]

Exactly what I was looking for. Cheers.

[@fink94]

Great content!!! I just can't get over how much I LOVE your accent!

[@defectdesigner1]

Thanks for the video, Colin! Can you do the same video about Nanotubes used in BluGuitar and Master Tube Design used in Taurus amps?

[@TyroneNorthcutt]

I wonder how many people just skipped to 3:55.... 😛 Love what you do brother, thank you for all the great info over the years.

[@ronniemoysey8854]

And missed the brilliant safety warning

[@saarangnarayan123]

Thanks for this! I have so much to talk about at parties now!

[@Christopherjazzcat]

Great sounding amp and informative video. Thanks for all you do mate.

[@sgtcaco]

Can you please do a in depth tutorial on plugging the power cable on. Thanks, made respect

[@fatpad00]

TATA- is there any difference between tube/valve amps and transistor amps besides the component doing the amplifying? I have a surface level understanding of transistors from some classes almost a decade ago, and all that low power contro circuits

[@AlexdeLarge6655321]

Hi Colin! I have a Vox VR30 hybrid amp. The manual is like a timeline of Nigel Farage tweets: it contradicts itself a lot. One part says the pre-amp is valves, while another says it's the power section that utilises the tasty tubes. I've never worried about it, because it sounds great, and just recently got me told off for 'coming in like an earthquake' when I insisted I didn't need to go through a mixing desk and could control my own levels in the local church, which I was suitably chuffed about. "Forgive me Father, for I have strummed."

[@rafaelbustos4758]

Thank you hope to meet you some time .stay cool

[@aspeguitars4071]

Nice amp, great distortion tone. The added digital(?) reverbish effect however takes the tone down. Thanks for your pretty well made video.

[@PooNinja]

Danger makes things exciting!! It’s why motorcycles are soo fun!

[@joedebono4012]

Great video very informative

[@chrisc2882]

I’m a couple old fashioneds deep but this is the video i was looking for

[@ForTiorIJohnny]

great video. here´s a follow up TATA - what makes two different amps sound different even though they use the same tubes?

[@ScienceofLoud]

The rest of the amp

[@MrMshossain]

@@ScienceofLoud then could you do more videos on why these amps sound the way they sound aka the rest of the amp. Like what makes a vox sound like vox or marshall stuff like that

[@TheCrimsonIdol987]

Colin said it right, it's the rest of the amp. When a designer is making a guitar amp circuit, they're carefully considering things like resistors, capacitors, potentiometers, and such within a certain tolerance for two reasons: 1. So the signal gets amplified. 2. For tonal reasons. As such, they consider vacuum tubes a mere component that falls within the parameters they want for their circuit design. These different parameters, tolerances, components, as well as the design of the circuit itself is what makes these amps unique. This is why, say, an Orange Rockerverb sounds different from a Mesa/Boogie Dual Rectifier, beyond the tubes they're using.

[@felinekaiju4517]

I'll have to watch this a few times to understand what I need to. I'd also like to make a dual rectification set up like the road king so that Valve rectifiers for clean and edgebof breakup tones and diode rectification for crunch and distortion.

[@shaunoleary8740]

That was such an excellent explanation, thank you!!!

[@MindsDozer]

i've got pretty strong comprehension skills and this stuff flew right past me. is there any prerequisite material you can recommend so that I can digest what looks like it would have been a very interesting video?

[@pooshNchums]

This is amazingly informative. Thanks Colin!

[@acook213]

Thank you, Scottish Macauly Culkin!

[@PJ-hn4cg]

I was about to start recording when my Fender Blues Jr. decided to quit on me. So I thought, hmmm , perhaps I can save some money by fixing it myself. Ha ! While this viedo was wonderfully precise and interesting, it only served to make me realize I am out of my league entirely ! I think I'd need a degree in electircity in order to comprehend the complexities. And, make no mistake, the warnings about tinkering around inside a tube amp are well taken. I DON'T want to die ! So anyway, I suppose I'll have to spend my hard earned $$$ - AGAIN - to fix this bloody problem !!! Methinks I'd do better to invest in a solid state ... 🥵

[@koyzumie]

Excellent explination and great visuals! Thanks for making this 🎉

[@johnmac8084]

Great explanation, liked & subscribed, thanks

[@mrgunn2726]

Great presentation, thank you so much!

[@silasfatchett7380]

Another clue that the AD30 operates in Class AB is the sag when digging deep. While all the output tubes are conducting, the current draw from the rectifier is constant, but increases when two valves are cut off, so there would be no sag if the amp were true Class A.

[@Yogi-Megan]

One of the best explanations 👍👍

[@AxelHavoc]

I'm looking into making my own tube amp. My solid state fender champion 100 made magic smoke. So I may put a tube amp in place of the solid state circuits. Since i have an empty cabinet now

[@andrecepeda1]

What an incredible video! Congrats!

[@jjclem8759]

Oh wow, I bought one of these around when they first came out, then, I guess, in ‘05. Sold it a few years back, just way too much for me to lug around between apts when I had so much other stuff. Now looking for my first tube amp since I started playing again and gotta get sth lower wattage.. I loved this thing tho!

[@tacos666]

Really really interesting topic ! I learned a lot, next video, more in depth on each part of the circuit component wise ;) I want to create one now ^^ Thanks a lot for all these informations !!!

[@Geopholus]

CS guitars. This video has a lot of good information, including a lot of facts that are often overlooked by typical forums or other guitar amp video's. You also have several confusing and or misleading statements, that I must attribute to who-ever came up with the script for this video. It is very good that You explain here, that this type of tube amp with an output transformer and a long tail phase inverter "attempts' (due to it's topography, and the behavior of output transformers coupled to typical voice coil / magnet speakers) to supply the speaker an output power, proportional to the input signal voltage. Most transistor amps (unless specifically designed not to) will attempt to supply an output voltage that is proportional to the input voltage. The tube amp circuit has an advantage for accurate coupling of power across the audio bandwidth for two reasons. Speakers generally have their highest impedance value at their resonant peak, (meaning lowest frequency limit), and lowest impedance about an octave higher than that, with a gradually increasing impedance as the frequency increases until the point at which the speaker ceases to be an effective transducer ( usually above 6 Khz). So at resonance a typical 8 ohm guitar speaker with a medium "q" may have an impedance of 12 ohms + at say 75 Hz, about 7.5 Ohms at 150 Hz, and an impedance that gradually increases to about 10 ohms at 6 Khz. A hi-end transistor amp would drive all the frequencies perfectly proportional to input voltage into a resistor load, but would be delivering half the power at the speakers resonance (unless compensated for), and proportionately less current to the higher frequencies, as the impedance and high frequency input goes up. The tube amp on the other hand attempts to provide output current proportionate to signal voltage so the output voltage goes up to the point where impedance loading, limits the available current. With most transformers and power supplies one finds in use, that increase is no more than about 20 percent. In most tube amps if You do not plug in a speaker, the output jack shorts the output transformer High side to ground, which,.. amazingly enough, usually doesn't do too much harm (overheating) unless the amp is driven hard. Most transistor amps will not survive this kind of treatment unless they have a current limit circuit built in. Conversely if one doesn't connect an output speaker or load as CS guitars suggests at about 14:58 the amps output voltage will NOT ATTEMPT TO REACH INFINITY, burning out the amp. The amp will attempt to increase it's output about 20 percent with signal present, and stop proportionate to the gain of the amp and the power supply voltage potential, (which ever it reaches first)... the other reason it won't do too much at all, except perhaps go into ultrasonic oscillation if it is an unstable design, is that unloaded the output transformers inductance , and therefore inductive reactance will increase many times over, so it will pass less signal, and almost everything it will pass will be at the low end, and so far out of phase that is will almost entirely be cancelled out. The only danger of unloaded tube amp outputs, are that due to the change in output transformer inductance ( which is normally nil when correctly matched to a speaker ) some amps with a lot of negative feedback, or generally too many stages of high frequency emphasis, can become unstable and go into high frequency (often ultrasonic) parasitic oscillation which can ruin output transformers, as arcs can appear across the primary. That is why most tube amps load the output to ground when the speaker is unplugged maintaining low inductance and phase linearity into a constant impedance load (which still amounts to an ohm or so due to the secondary's resistance of the output transformer itself). Your description of class "A" and class A/B & B is fair but not entirely accurate. This Orange amp is being operated in triode mode (no screen grid resistors) and Cathode bias so it very likely really can't deliver 30 watts rms. It is probably slightly out of the pure class "A" push pull, and at least slightly into class "A/B". Unless the power supply voltage is really excessive, I'm guessing this amp does about 15 -18 watts rms when adjusted as far into class A/B as it can goes. Of course with the output doing almost square waves as You show on the 'scope at 7:10, that could be close to 60 watts worth of square waves. Clipped square waves deliver 4 four times the power of clean sine waves.

[@silasfatchett7380]

The output valves do have screen resistors and are working in pentode mode.

[@Geopholus]

​@@silasfatchett7380Yes YOU are CORRECT. I stand CORRECTED, in terms of the tubes operating in pentode mode and that there ARE screen grid resistors, my bad. But If this orange amp were truly acting in class "A" mode throughout it's range, meaning until You reach the power supply "ceiling" at which point the amp starts clipping, the amp would still only reach an output of about 11-18 RMS sine wave watts. because for all intents and purposes the tube is operating ALMOST as though it is in triode mode because neither output tube ever shuts off fully. If operating in a fairly lean Class A/B with tubes in pentode mode, the specified output for 4 EL84s is about 36-38 watts. There are some very rugged EL84s that can operate with higher than specified power supply voltage, into Output transformers with fairly low impedance that can produce slightly more clean power,... but if class "A" You still don't get into the 30 watt area. I understand what they are saying about "class A, most of the time, which is where many class A/B tubes amps are anyway, with an overlap of + & - waveforms somewhere between 25 & 60 %, but that is really not class "A". Single sided class "A" with its emphasis of 2nd harmonic (2 x fundamental) sounds noticeably different ("warmer") than class A/B or class "A" pushpull . But with 4 EL84s running in parallel with single sided class "A" (in triode mode) that would give you perhaps at best about 6 watts RMS. When overdriven into the square wave realm, 4 EL84s, in class A/B can produce about 120 watts or more of "peak power."

[@mattheweady615]

Can I ask what camera you use for your videos? They are very high quality :) Great content by the way

[@rileyioacura]

KZbin seemed to have unsubscribed me which I didn’t know.. so I’ve subscribed again

[@JoeMueller-v6c]

Colin, your videos and succinct explanations of these various topics are brilliant. I’m probably not the first to ask, but have you done any content on “valvestate” amps? Or would you? I own a Marshall AVT150 that I acquired years ago and played it for a little while before moving in the direction of Fender tube amps. I like the idea of acquiring another Marshall but I’d like to explore what that AVT150 can/can’t do first. Anyone’s thoughts are appreciated! Thanks

[@rossbalch]

Does anyone know why preamp tubes have the metal jacket? I've noticed some tube amps use them and some don't.

[@woodchucksquirrel]

I think it's to reduce interference.

[@allenwarfield9262]

Yes, it's a tube shield to prevent interference from power supply and transformers. They also usually contain a spring which will keep the tube locked in the socket, preventing vibrations from unseating them.

[@marinosvafeiadis2655]

Great video! However please explain how you managed to connect the reverb/delay rack since there is no fx loop on this amp!

[@rikwylde6074]

I have no idea what the Mad Scientist is talking about! But I love to listen!

[@calyodelphi124]

That phase splitter circuit at 8:30 is a long-tailed pair in vacuum tube form! :D en.wikipedia.org/wiki/Differential_amplifier#Long-tailed_pair

[@frankdstrack]

I would love to see one of these on how attenuators work. 🤘😫

[@jerryjones698]

Where did you learn all of this?being able to work on your amp is valuable knowledge

[@trevorjohnson8142]

Thank you so much; this video is perfect!

[@stayoutoftheswamps]

Suggested TATA, how does channel jumping work and how do different 4-input amp circuits compare?

[@IanHaghighat]

I was hoping there would be AD30 content!

[@rydinorwin]

Fantastic vid man, many thanks!

[@alexcorona]

It was well before the 60s, I have a solit state amp from the 50s and it sounds fantastic. Germanium transistors an all. Just had to replace the caps that went bad. Other than that shes a beauty.

[@Lukas_Hart]

Nice explanation! Very interesting and understandable, well done. :)

[@timburle4980]

Great explanation!

[@bpabustan]

Again, AMAZING AMAZING AMAZING VIDEO! But here is a nagging question: do power tubes have an inherent tone? Let me elaborate: When we talk about Fenders (a Twin Reverb for example) - we automatically think of the 6L6GC power tubes. On the high gain side, the Mesa Boogie Dual Rectifier Then when we talk about Marshall (a JCM 800 for one or say a Super Lead) we automatically think of EL34 tubes On Vox AC30, we think of EL84 tubes. We guitarist can almost instantly know each amps sound without looking at it themselves That is why I asked that question. Ceteris Paribus, can a Twin Reveb still sound like a Twin Reverb if we use EL34s? Or will a JCM800 still be JCM800 if it used 6L6GC?

[@ErebosGR]

The differences are subtle but notable. There are amps designed to work with either EL34 or 6L6s and they do sound differently depending on the valves used. There are even amp sims that let you change between different power amp valve types and hear the difference with ease.

[@bpabustan]

@@ErebosGR thanks for that reply. Then what's with those tubes that gives them their own sound?

[@ErebosGR]

@@bpabustan Different grid bias voltages, the design of the control grid and plate assemblies, size and shape of the tube etc. In short, they amplify the input signal slightly differently because of their design.

[@bpabustan]

@@ErebosGR ok I am beginning to understand: the tubes not only do they look slightly different but also work "quite" differently too. Got it! 😀

[@bpabustan]

@@ErebosGR thanks so much again! 😀

[@Merjia]

It's saturday night, I've got my dram of Laphroaig, lets go!