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Hello Paul. Really enjoy your videos. Thank you. What is your opinion on whether same spec valves from different manufacturers really make a difference to the sound of audio amplifiers? For instance I have seen vintage NOS Telefunken ECC83/12AX7 valves (similar to those in the Harmon Kardon Citation you serviced recently) selling for £150 or more vs other makes for £10 - £15. Is there really any justification for this large price range? I can appreciate that some valves are more microphonic than others but many claim there are tonal and other subtle differences. Perhaps you could make a short video either debunking or confirming the facts on this sensitive issue. Keep up the good work and excellent content.
Thank you for your input Sharkey. The video would be great. I'm not so sure if people can handle the truth when it comes to this question. I find many want to believe in magic. The video would be controversial, that's for sure.
Hi Paul. Yes I am sure it would be controversial, my belief is that one strong tube sounds the same as another but I don't have "magic" ears like some. Perhaps you could do a video specifically about matching valves, why and where it is important. ie phase splitters, stereo gain stages and outputs. I have valve hifi amps but rarely use matched valves in anything but the output stage. I am interested to know what matching tolerances are acceptable especially in phase splitter circuit. Perhaps a demo illustrating the circuit with mismatched tubes vs matched and the problems if any that arise from mismatched tubes. Which characteristics are matched by vendors, ie. In the past I have bought GrooveTubes EL34s in matched quads. GrooveTubes claim to match their tubes for gain AND distortion, How is this achieved, is it just marketing.
You make things very clear and very understandable to folks like me. I don't know much about electronics but this was fascinating. Thanks for not talking "above" me.
I find myself more and more these days, in a state of awe and wonderment. The fact that resources like this exist, of a quality and depth that would have been unthinkable just a few years ago, for nearly anyone and everyone’s benefit...seriously, what a friggin’ time to be alive!I’ve got to remember not to take it all for granted more often. I’m light years from being considered a professionally competent engineer. My career certainly has a heavy technical aspect to it, but I also have just an insatiable curiosity when it comes to understanding the world around me. Thank you for sharing your knowledge. Thank you for making these videos. Their value, to me, is inestimable.
I know right? I don't have a ton of cash so I try to spend what little patreon money I have on people I feel really make a difference. As soon as I saw the first couple of videos I jumped on his patreon. Paul is amazing, super easy to follow, incredibly thorough and the test equipment that you build in his course are almost beyond belief in their abilities, especially the SIFT capacitor tester / Prognosticator and the Super Probe. I'm like you and far from being anything more than a Simple hobbyist. These videos and the test gear that you build have me much closer to the "Somewhat Advanced but not a pro" Level...
The resource that is amazing and beyond belief is Mr. Carlson himself. Everything you see around you was once a thought in someones or somethings mind, even the stuff not man made.
You are so correct sir. I got really serious about electronics troubleshooting around 1999 or so. I was about 17. I used a lot of Internet newsgroups back then. It wasn't great all the time, but now, it's just amazing what we can do and learn. The funny thing is when I wanted to start learning about repairing power supplies and things like stereos and tvs, everyone said I was wasting my time, that nothing is worth fixing anymore, etc. I didn't listen to anyone. I did what I wanted to do and i'm happy with that. I got such tremendous pleasure out of fixing an old 14" CRT monitor then, and I still do to this day. I don't regret my choice at all. This channel and Mr. Carlson help me get better at this, and i'm grateful to him for that.
Haha the battle between musicians and technicians...awesome. Good explanation with the load issue. I had a Boogie Dual Rectifier on the bench once and some guy had stepped over the speaker cable on stage at full power disconnecting the speaker from the amp. The plate voltage sparked into the heater as it is the closest thing to it and evaporated the metal clips in that socket completely. After replacing the socket luckily the amp worked fine but this could have been a total blow of the complete amp easily. I wonder why manufacturers are not putting over voltage protection into there amps. I use 2x 1N4007 in series reverse at the plates to ground which gives me a 2kV protection and if these blow it is much cheaper then everything else that is in an amp. Another great video and awesome stuff on Patreon!
15:58 props for mentioning 'doghouse' cap can cover. A lot of times they cannot even be there, making for interesting times for hands checking out the speaker connections, or pulling the chassis as the output transformer is right there and a go to for leverage. The last high-powered UL pro I was in which is almost exactly like that 70's twin you have had 525 on plates, and although it was functioning well, one of the electrolytic under the dog house had intermittent connection so free to charge I would imagine. Pretty sure that design uses two 350V 220uF in series for 110 + - at 700V... Lately I've been reading people's know-it-all Stance that there's not enough electricity (current) to kill you... I invite them to give a lick to the guts, or would they allow their kids, or pets to play in there. Heck I washed my car and touched the auto garage door track and shocked the hell out of me.
Hi Paul, I did some checking with a 10uF e-cap in parallel with a 10K resister, and my Peak Atlas LCR45 tested the cap better than my Brymen, Fluke, and other meters. I didn't expect that.
Was an owner/operator of an electronics repair shop, did warranty and non-warranty repairs for some major manufacturers of radio/tv for almost 40 years. I still learn from watching the workflow of others. Enjoy your videos... loved the Hammerlund restorations. Keep up the great work... Rich
You know you are getting old when they start talking about old Fender Amps that are the black tolex. I worked at Fender or at that time CBS Fender Musical Instruments assembling Twin Reverbs and all the others like Quad and Super Sixes. I also assembled all the Speaker Enclosures like the Baseman and Dual Showman. At that time everything was built in the whole plant by piecework another words you were given a standard you had to build in an hour to be equal to your pay. If you built more than that an hour you got a percentage on your hourly pay like a raise. There were like 4 people remember that could that could build at over 200% with zero issues and I was one of them. For instance, a Twin Reverb had a time standard of 9.6 an hour for 100% of of your pay. I could assemble them at 20-21 an hour. So that equaled like over 200% of my hourly pay, which making double your hourly wage was pretty good pay back then. If you did less than 9.6 you still got your regular hourly pay, but you were not going to last long if the company only got that out of you. The only problem was that if you turned in over 200% they would send down the Time Studiers to adjust the standard they really wanted people to only make no more then 150% so us top assemblers would stop working at the 7th hour and just sit around until the shift was over. Boy do I have some great memories of all those guys I worked with and the great times we had together. Glad to see they are still working out there.
GentIlemen, I've been doin tube guitar amp repair for a living since 82. I used to do Fender warranty i n the 90s. I got to know Fender employee,John Fouch. I saw a picture of Nez Pierce leader Chief Joseph from 1890s. The photographer was Johns ancestor.
Jeff thanks so much for Your post, and work. I am sure many of the amps I still see alive and Kick'in ass are the result of Your work ! Fenders are my favorite amps to work on!
Jeff Hook, what you describe is exactly how management operates when I did machining for an aerospace and aeronautics company. If you found a way to beat the time standard, you dare not beat it by too much because you wouldn't get a raise or a bonus; you ---- and everyone else --- would then be expected to make those "extra" parts each and every time!
I have been working on electronic equipment for several years now and have even taught a rather condensed and relatively advanced electronics course recently. I must say that I've always loved my field as a total science nut, however finding Mr. Carlson's videos has changed everything for me. I didn't expect to find someone so in touch with this world of electronics. This is either formal training as an instructor or the greatest naturally talented instructor I've ever seen, and I've met many great professors and teachers. Mr. Carlson has turned my profession into more of a passion than ever before. Watching Mr. Carlson work is a very humbling experience for me as it shows how much there is to learn as well as how exciting electronics can be!
I'm here as a musician that uses tube electronics that is quite interested in them, except I usually sit right around 40 to 150 hz, as a bassist. It's funny you say that about the master volume twin reverb, Fender actually made them less prone to distortion(not that a regular 85 watt Twin is pleasurable to be around at that volume), I had read that it was due to a shift to ultralinear output transformers. I've never been able to drive a UL 70s Fender amp to the point of overdrive that wasn't painful to be in the same building with. Even as a bass player, running my 8 ohm UL Studio Bass(200w, "enough") into a 4 ohm load it was still hearing damage volume at power tube breakup. Incredible amps, these are. I've learned so much over the last two days watching your videos about tube electronics, easily the best electronics videos on the internet.
You, along with Uncle Doug, DLabs and The Guitologist, are by far some of the best channels on youtube for troubleshooting vintage gear. Props to all of you. Invaluable information.
Hi @@UncleDoug I just watched your current limiter protection video and I have one question. What does it matter the black wire or the white wire for the bulb? I thought AC was AC and both sides were in effect the same? electricity is fascinating and channels like yours and electroboom make things simple enough for an ignoramus like me to understand. Thanks for teaching mate. New subscriber
What an enlightening video! I was hooked as if I was watching a good detective film. An hour and six minutes flew by in no time. Please make one about a solid state circuit.
Your warning about high voltages reminded me of a time in High School Electronics class when we were dissassembling old computer monitors. One student was gone when the teacher explained how to properly discharge the tube capacitor. There he was taking the monitor apart. We asked him if he discharged the tube. He looked confused. We explained the high voltages inside. He carefully put his screwdriver down and slowly backed away from the workbench.
Your channel has quickly become my new favorite. So much knowledge and such a good teacher. Lesson #1: RE-CAP EVERYTHING. I've learned so much about capacitor failure from watching your videos. Keep it up Mr. Carlson, you're awesome!
At 32:27 or so, you tell us how to explain to a customer how we need to replace the wax caps for the amp to be dependable. All it takes is one customer to tell you, "You've destroyed my sound!!" and you realize that another tactic can be added to placate them before you start replacing caps. Basically, what I do is draw a small trapezoid (triangle on its side) on the left side of a piece of paper, and a larger one on the right. Then I tell them that the trapezoid on the left represents the guitar input, and the one of the right is the output. Next, I tell them that what we want is for the output to be an exact copy of the input, which means that the amplification chain has to be very linear for this to take place. "If you want to have a particular tone, the best place to insert this tone is before the input of the audio amplification chain." I then explain the use of guitar pedals. "They are distorting the audio signal of the guitar; however, what is important to note here is that the audio-amplification chain will duplicate this signal exactly, as it's a linear amplifier, and if I don't replace those wax capacitors, it won't be able to amplify in a linear fashion. I will show you how to duplicate your tone, once we have the amplifier working correctly and safely. I also tell them about possibly destroying the amp, as you do, Paul, for added impact :D. Another thing you can do is go here to UA-cam and show them what happens visually to improperly-biased tubes. One good red-plating video speaks 1000 words :D. I've often thought about injecting a two-tone signal into the amp and displaying the output on a scope of their amplifier in a before-after analysis, but I haven't had a reason to get this far -- AHEM! -- yet :D. That day will come soon -- I'm sure of it! Another thing I do is explain the reason we want to use high-quality electrolytic capacitors in audio circuits. Some might say this is overkill in a guitar amplifier. Maybe. OTOH, when I tell them that this amp will sound so good that you could also use it for semi-decent HiFi audio on their computer or home entertainment systems -- although it will increase the repair cost a bit -- I get an instant "Do it!" from them, and all is good :D. Should any of them doubt this, that's when I turn on my Deluxe Reverb and play a song they are very familiar with, folks. That seals the deal completely, and from that point on, you are thought of as the local amp guru, even if you deserve that moniker or not :D. It's all about the marketing, especially with people you don't know. Show them things visually and teach them verbally, because this is how most people have been taught to learn. It's also the reason UA-cam is such a great resource for learning as well. 73...
@@domi7007 I take it you're talking about the amplifier for ham radio, as in the LDMOS amplifier? Haven't played around with LDMOS just yet. Too busy fixing guitar amplifiers and old tube radios for my collection. A lot of folks are learning to play guitar during the coof, and that industry is booming. Here's an interesting aside. I watched a video from Premier Guitar on Brain May's setup that he uses while playing. He uses an old VOX amplifier, and he removed the negative feedback so his amp distorts easier. Doing my homework on audio amplification, I've found out that this would allow him to use fewer pedals, and the more pedals you use, the more noise is introduced via amplification. Personally, I'd never go this way. One would think that doing so would be a bit harder on the tubes in the audio-amplification chain in the final, but now I'm not so sure that my original assertion is totally correct. LOL! OTOH, it is my belief that A.I. is going to completely change audio amplification, and it has already done so, via something known as "modeling amplifiers." I'll step out on a limb here and say that all new amps will be modeling amplifiers, in the not-too-distant future, and pedals will be a thing of the past, although I'm sure will still see a ton of purist.
It would be nice to see a Part 2 of this video testing the Electrolytic Capacitors and replacing them, Testing the Output tubes and looking for matched pairs and also Biasing the amplifier. Thanks
I signed up today for Mr Carlson's Lab Patreon $20 per month option because need to support quality videos like these - Very Well Done!! I look forward to learning more on your Patreon area.
I worked as business equipment engineer for many years and I used to service automatic bank dictation equipment I.e. connected to telephone exchanges. The GPO engineer at the exchange told me the painters were in to brighten up the rooms around the equipment. There was racks of lead acid batteries all connected in parallel for power backup if the mains failed! they remarked “it’s safe enough as the total voltage is only 50 volts! They forgot to mention that the total current available was massive (several thousands of amps) There was a huge bang when somebody dropped an aluminium ladder among the terminals and part of the ladder simply melted! Lucky nobody was injured! H S wasn’t very strict in these days! Fraser
Old ground based aircraft navigation transmitters had 250 VDC as low voltage, 750 VDC as medium voltage, and 12,000 VDC as the high voltage with plenty of current. You paid attention really well when you did anything at all, anywhere.
Got a Twin Reverb like this sitting across the room from me that I bought in 1976 except it's an earlier 100w not 135w. Had it modified with a Rivera/Boogie sort of lead channel and used it from Egypt to Japan and points between back in my traveling days. Briefly had a 70w Pro Reverb which should be nearly identical to this Twin Reverb except half power. Now mostly use one or two of my other amps (69 100w plexi. 79 50w Marshall, 68 Bandmaster, a couple of newer Ac30 types) these days. I don't have as many amps as some folks but love them all, especially my Twin Reverb because it was my first REAL amplifier. Great to see Mr. Carlson feature this Twin Reverb amongst the vast array of gear he deals with.
On that kind of old amplifier, you cannot keep everything original more than about 20 years. Just because the capacitors don't last forever, especially the electrolytic ones. Same thing for the carbon resistors, they tend to become very noisy and unstable. You'll never get the original sound as it comes from the factory, just because component values tend to change through the years. If you prefer noisy stock amplifiers, it's your problem!
Hi Mr. Carlson, I just wanted to say thank you and tell you that your Patreon program has been so informative and valuable to me. It has not only taught the fundamentals of electronic repair but given me and the rest of your patrons the information and even the tools to troubleshoot the circuitry all the way down to the component level. It’s been an amazing bit of information and I can see why so many are joining up. In addition to learning, it’s been a lot of fun and I look forward to every new video. When I saw this video today, it reminded me of that. I know that this isn’t as easy as it looks, you don’t just sit down and knock out these videos, it’s a lot of work. Like I said earlier, I just wanted to say thank you, I’m having a great time! -Buddy
I agree. I became a Patreon months before I planned on starting to build anything because I knew that the information, projects, and teaching was worth much more than what I had to pay to be a member of Paul's Patreon channel. Thanks Paul!! You're the greatest!
What is sleep but a waste of life, sleep less, power nap and get more done, including enjoyment, life's too short, a couple of years ago I was 28.... now I'm 62 OMG where has it gone????
😢started learning electronics in the mid 70s from a tv repair man who was also an electrical engineer also tought me math that i could never grasp in school learned mor in 3months of working with him then i did the entire time in school you remind me much of him in my 60s now cant see for sheit but love whatching your videos makes me really miss my electronics
Thank you Paul for sharing this Patron video, because of it, I was made aware of snubbers in a bridge rectifier, then doing some research, learned of their value. Cheers, Adriel
I translate musician terms to engineering terms. What they talk about most is "tone." That refers to the overall characteristic sound of an amp. They aren't crazy, and they aren't really being picky. They have a sound that they like and they want to retain that. The plate resistors may have increased in value, and increased headroom. If they like that, you need to either install a corresponding current value of metal or carbon film resistor or just leave it alone. The original may read 120K instead of the marked 100K. But with caps, leakage is the worst thing.
BOY you are the tech EVERYONE WANTS....methodical...thorough....detailed.....you're TERRIFIC. VERY experienced. So great....THANKS Paul....(UNCLE DOUG....TWO OR THREE others.... such good tutorials.). Perfect for me. Your a GIFT really. Thanks again!
4:29 - ALWAYS take the user's 'diagnosis' with MANY grains of salt! Also, I can't help but wonder if it does turn out that all the electrolytics are original and the cost of replacing them would exceed the claint's budget, does he just take the amp to the dump? That would be a real waste!
If the customer doesn't want to pay for new caps in an old amp they're bloody crazy! "Here's your $2000 amp back that you don't want to spend 2 or 300 dollars on. Now piss off & take it to some dodgy tech you halfwit!"
And the hotter they get the better they sound! Right up until they break down. I've seen black goo oozing out of transformers (melting the potting compound) at midnight in a crowded venue. Man those amps sounded great! There's something about pushing them past their advisable operating limits that makes it all sing (until they break down).
One problem that I saw when fixing Fender amps took me years to finally get to the bottom of. Several Fender amps that I saw would have random "shot noise" that sometimes sounded like lightning interference on an AM radio, sometimes it had random whistles and squeals mixed in. I traced the noises to something in the interstage coupling circuitry. If I squirted the fishpaper and eyelet "circuit board" that Fender used with contact cleaner, the symptom would go away for a while, but would reappear once the cleaner evaporated entirely. Yes, I was mindful of the high voltages while doing that. The few times that I fixed it, I ended up removing certain tie points from the paper and letting the connection float in the air. I learned years later when working with other equipment with high impedance/high voltage connections that after the passage of decades, solder rosin flux residue becomes a noisy resistor. I now know that the original removal of the flux at the Fender factory had driven a small amount of flux into the paper which years later would cause the noises we heard.
Wow that's interesting Dobbin! I thought you were gonna say something about leaking electrolyte from a capacitor making the cardboard or elephanthide rivet panel conductive! But flux doing that? I'd never have thought.
For such a seemingly young fellow, you seem to have knowledge way beyond your years. Most thorough and comprehensive videos I've ever watched, and they are great.
Thank you so much Paul. I have watched many, many videos on tube amp servicing and followed along sort of understanding what was being said but the way you explained each step finally made the light come on. (No pun intended). I hope you do more.
Hi Ken, you are very correct about the microphonic aspect of ceramic capacitors. If they are used for bypass, and are not in the audio chain (or have been chosen for a specific quality) it's ok to leave them in circuit.
Yes. I should have said that I replace only the ones in the signal path. And, only if they are particularly microphonic. Otherwise, there is no need to replace them. Cheers!
It is always good of you to issue the warning about HIGH VOLTAGE. One time, as a young teen, I had a Motorola 2m VHF radio powered up. Managed to get the b+ across the chest and that really, really smarted. Worst shock I took. Of course, tube gear was the only readily available hobby material in the mid 60's. I did take a number of shocks and drew many sparks. I never got use to either. Later on, I learned to keep my left hand in my back pocket when probing live circuits. For those new to these circuits, make sure your scope probes can take the high voltage as some cannot. Keep the ground clip on ground.
I MY SELF have built a Marshall 18 watt amp . and also a fender champ 5f1 with my brother. 12 ax7 6v6 I like el 84s tube amps are great. have had a line 6 dig 75 watt spyder 4. Thank you Mr carlson for your great videos.
Love your videos. However, it makes me cringe to watch you point at live circuitry with your fingers so close to high voltage. Maybe it would be safer to use a non-conductive pointer and keep that second hand away from the chassis. Am I wrong in my assessment? I admit it terrifies me to think of working on a live chassis, or even one that might have residual charge in its caps.
The standby switch disconnects the caps in the capacitor tank from the bridge rectifier, so discharge them at the low end (away from the rectifier) of the standby switch for safety before sticking your fingers in there!
New subscriber here. Love your videos! I was working on a 1976 Fender Vibrolux about a year ago for a friend (similar vintage, but smaller amp with roughly 40 watts output, if I recall). I have another friend with the knowledge and test equipment who went through the chassis for me. I was mostly taking it apart and cleaning 40 some years of filth out of the thing. Other than replacing the tubes and cleaning some crackly pots myself, after he was done, my work was mostly a cosmetic restoration. Got it back together, plugged my guitar in, and it sounded great! Just like new! Returned it to my friend. He loves it! There was one step I found later that we had not addressed, wherein lies my question: adjusting the bias. There is a small nylon screw on the tube side of the chassis which was on or near one of the transformers. The Vibrolux, being smaller, is only powered by 2 6L6s, hence one bias adjuster screw. I believe the Twin, as it has 4 6L6s, has 2 of these bias adjustment screws. Could you do a follow up video, once your amp is back together and running, explaining the importance and/or procedure to this process? Another music/ gear-head friend of mine said that bias adjustment is important and I should get the amp back and have this done. I did go to the trouble of buying a matched pair of 6L6s, but think that bias adjustment may still be necessary. Would love to hear your thoughts on this!
I've been working on the "CBS" Fenders since the time they were new, and the black face Fenders since the time they were 1st released. Yes on the high flying filament wires. The black faced Fenders had cloth covered solid core wire that took a higher tight twist so they tend to be less hummy. Yes the 'blue molded" poly caps almost never fail.,and yes the mallory filter caps usually have to be replaced, even though often times they "still work",.. the electrolytes dry out. The one error in design seems to be the tremolo cap that You reference at 45:12. since the tremolo circuit tends to oscillate between a cathode follower and a common cathode mode, that cap sees way more than the 25 volts it is rated for, although the current is really low. I usually replace them with a small 200-400 V electrolytics that are now readily available. 10-22 UF. The Fenders are set up to play the output into a shorting speaker jack, when the speaker is not plugged in, which is much better than leaving the xformer open. I ALWAYS plug in a resistor dummy load with a speaker divided off that load, so I can see what is going on, looking at the signal across the load resistor.. Silver face Fenders often suffer from parasitic oscillation resulting from a change to the circuit (by CBS) with the bright switch wired so that the 250 pf cap sees a resistor to ground, creating creating 360 degrees of phase shift at some high freq (20-100Khz). That resistor, though not in any schematic I've seen, is hidden behind the brite switch and a bunch of wires. remove it! Silver face Fenders have a lot of problems created by the "hiFi" engineers from CBS. However the Transformers are better quality, but not necessarily to many guitarists taste. The bias balance control is not as good as a bias control for instance. Nice to see and hear Your excellent analysis , that brings up some things i seldom think about.
You got me. I love Fender amps but the 135 watt Twin has around 500 volts on the B plus.They arc power switchs and tube sockets,they are "anvil in the forehead loud".Now that I got that out,all new Sprague electrolytics,new JJ 6L6s,new Tungsol 12AX7s,new EH 12ATs.Better yet sell it and buy a Deluxe Reverb.
29:20 - The output stage is basically an AC current source. With no load, you get a *major* voltage-rise if you were to crank it up! The output transformer would arc and inter-winding insulation would melt!
"Don't replace the bumblebee capacitors! They are vintage and sound better as they age! The new ones are fake and don't sound as good!" - I hope you like your blown amp in a few months then.
I feel you have a lot to contribute to people wanting to better themselves in the field. Maybe you could do so with about half the words? I mean, if someone is watching this to figure out how to fix their amp, and they really need a in-depth explanation of how capacitors work, they're probably a bit in over their heads.
One thing I would add when probing around with an AC coupled scope probe, dealing with wide voltage swings on valve equipment, is that when moving to different parts of the cct, always ground the probe to discharge the DC stored in the coupling capacitor in the scope. Not so important with an all valve set, but if you were to put the probe onto a OP amp or transistor after you have been looking at an anode of something, a few hundred volts could cause an unhappy weekend.
I think it's best to do that after every measurement tubes or otherwise unless you are going right back to the same point in the circuit. It's actually a very easy habit to get into just like when you take high voltage measurements or are probing a high current environment always position your probe so that if it slips off the connection it does so in such a way as it doesn't short anything out. It's all in the way you apply touch pressure to your probe connection.
Aaaargggh! Don't worry about it. Most coupling caps will not be rated much over 50v, because most scope inputs can't withstand high voltages (not designed to). This is why you have a x10 probe, (also for bandwidth of course), to extend your vertical range. The probe has an average 10 million ohm impedance. Nothing is going to happen here - never has to me, and shouldn't to anyone else. Certainly there will never be 500 volts sitting on that cap...The probes are cat rated - or should be - and will be rated to a certain voltage.
@@martinda7446 I don't want to be looking at what's on a plate in an intermittent circuit and then just stab at the next grid and send a spike all the way down stream possibly "healing" the problem.
Excellent, I appreciate all the tech tips. Had a Fender Twin Reverb back in the 70; this thing eats speakers, as they were not matched for the power of what this amp can output. Also, the Reverb circuits are not too reliable. Otherwise, it's a lovely amp. The high voltage warning cannot be overemphasized.
This was excellent! The way you pointed out the signal path in the chassis and how that corresponds to the schematic was what I've needed to know. I've watched others explain about the circuitry, but nothing comes close to this.
Mr Carlson, I love it.Fender amps even of this era are like working on an old muscle car .I've owned my share of them my friends play them .They are the sound of rock,jazz,blues and American music in general.
AcceleratingUniverse I would not say that only for-sale videos deserve attention in the making. But as you are speaking about paying: are you aware hat we actually pay for these videos?
Guitar players pay big money for vintage, “classic” tone that modern electronic components (resistors and caps) - even with vacuum tubes - don’t reproduce. That’s why these guys are super touchy about what you replace and what you replace them with.
Hi Joe. I guess what isn't understood is: The amplifier parts are degrading now, and only now do they sound like that, (classic sound.) After the amplifier is rebuilt, it would sound closer too the way it did "from the factory" when it was released. Whats even more interesting is: People don't realize the magic is in them, not the amplifier.
You never fail to amaze me with your info and teaching ability, Thank you. Beings that I am a T-shirt junkie, have you thought about any advertisement bits, coffee mugs, T-shirts, just some odd and weird stuff that has your logo and channel name printed upon them... Try a small batch of test T-shirts, let the fan base know this is just a test run, of only 50 , just to see if this avenue is worth the effort on your behalf to deal with, setting up, like your time isn't already consumed, but, I would buy a T-shirt and where it proudly
Thought it might be worth adding that when testing transistor or valve amps, there are different considerations as to loading the speaker output. With a transistor amp it's generally quite OK to run it with no speaker or dummy load connected, even at reasonably high signal levels. The thing that will damage a transistor amp is a short on the output, and the damage can occur literally in milliseconds. Transistors can pass high currents because they have inherently a very low internal resistance. Even if the amp still works after the short, it may have been damaged and pack-up a while later. Since many such amps are DC-coupled, an output short with no signal can still do damage. As can shorting the output soon after de-powering if the supply caps are still charged. A problem can arise here with certain 1/4" jacks and jack sockets, where the jack tip can ground-down momentarily as it's put in or pulled out. The momentary short this creates can do damage. A Speakon or XLR connector is preferable. Somee people imagine that the fuse will save the output transistors. It will not. The fuse is there to prevent a fire. On stereo amps, never parallel the two channels to the same speaker. This is effectively the same as shorting both outputs, and is very likely to do damage. Some of the more powerful units have bridge outputs, on which both sides of the speaker have signal voltages. Therefore, never assume that you can safely ground either terminal of the speaker, for example with a scope probe shield. A further concern is that a fault in a sold state amp can destroy the speaker by putting DC onto it. Therefore, either use a speaker you can afford to lose, or test with a series resistor (say 100 ohms) to limit the current. With a vacuum tube amp, it's a rather different situation. Tubes have a high internal resistance, so the short-circuit current is inherently limited. An output short will generally do no damage so long as it's not sustained long enough to get the anodes red hot. Running the amp with no load at high volume though, will cause abnormally high voltages on the output transformer and tube sockets, and may cause a flashover. This is even more so if there is a faulty connection in the speaker wiring which makes and breaks. (That output transformer is basically a car ignition coil on steroids, and it will want to produce a spark if the circuit is suddenly interrupted.) I would always take a close look at the output tube sockets, and replace any that show tracking marks around the anode pins to any nearby ground. This is usually a sign that the have arced in the past, and once the insulation is weakened they may do so again. So, test solid state amps either unloaded or with a dummy load, but be especially careful to avoid shorts. Test vacuum tube amps with a dummy load, and beware of bad connections. In either case the dummy load need not be exactly the speaker impedance, somewhat higher resistance is better than lower though. A series resistor for your test speaker is also a useful addition, allows monitoring at low volume, and won't pass enough DC from a faulty amp to burn your speaker out. HTH. These video bring back fond memories of my time on the audio bench. In some ways more rewarding (and less frustrating!) work than maintaining computers. Oh, and do heed the safety warnings. They are not exaggerated. There are some truly evil voltages in guitar amps.
@@micametalgem3721 Hi mica. I agree. Much safer to connect at least a 100 ohm or less resistor across the speaker terminals just in case. You may accidentally cause a 'blurt' by touching a test probe onto a grid with your finger touching it (hopefully not!), or something similar. This 'blurt' may be enough to damage the amp. I don't think it's worth risking a $2000 amp by simply not connecting a resistor across the speaker terminals, especially if it's someone elses amp!
You use ge silicone II, too. I use it for heat shielding especially on induction coils. I put about 1/2” layers on them.. I’ve gotten inverters , high power drivers, fet’s etc to last for years using this method.
Very much enjoyed this video. Your skills far outweigh mine and that comes from learning and experience, something I hope to also acquire more of with the boost from your excellent presentations. 73's de N9ZN - Tampa Fl.
Thanks for this video. It helped me as I worked on an older Crate Blue Voodoo 6212 combo amp. Your videos are extremely good for building confidence in the repair process. Thank you!
I want to thank you for reteaching me electronics. Please keep on making more videos as so to benefit a lot of the newbees who have consent to go down this wonderful road of discovery.
You have the best videos ... Outstanding information!! WELL DONE!! Would enjoy to see a video sometime with your outstanding detail to know how to get that buzz/vibration out of Treadmill type DC Motors when they are under load ... Capacitors vs. Choke (Coil) ? ... seems to be a common issue with MC-60 Variable Speed DC Motor Controller using a 5K potentiometer ... I can put my DC Power Supply from my workshop to run my Treadmill motor and it is silent ... but with the MC-60 board it needs something to smooth out the DC power from the Bridge-Rectifier ... Thank You again for making your videos.
LOL, I know that simply because the video is posted, all is well but every time you point to a component in a live circuit I cringe. I also understand the foreshortening the video camera has but, ........ still, ..... it creeps me out :P AGAIN, another excellent video. Thank you!!!!
20:10 when I worked at an auto parts store, and a customer came in with a part, from a reputable manufacturer that did not last as long as it should have, I would say, "one day someone sneezed on the production line and part just won't last as long". You can make the best parts in the world, but you can't defeat statistics. *someone* has to get a bad part sometime. A mote of dust in a switch, greasy fingerprints on some solder joints, a worker had an argument with their spouse; the best factory in the world can't control all of that. If the company has a good reputation, and they make it right, you might want to give them a break.
Thank you for this video! I am finally getting back into electronics. It is finally time to see what the heck I messed up with my guitar amp build I did way back around 2008. I was young and while I learned a lot, it wasn't nearly enough. I just hope I don't end up spending a lot on more components. I easily spent $300 or more on parts alone for one of the most simple tube amps ever.
To learn more about electronics in a different and very effective way, and at the same time support this channel, go to Mr Carlson's Patreon page, click here: www.patreon.com/MrCarlsonsLab
the absolute madman, he actually did it
please teach how to download a copy of your brain into mine, thank you :D
Hello Paul. Really enjoy your videos. Thank you. What is your opinion on whether same spec valves from different manufacturers really make a difference to the sound of audio amplifiers? For instance I have seen vintage NOS Telefunken ECC83/12AX7 valves (similar to those in the Harmon Kardon Citation you serviced recently) selling for £150 or more vs other makes for £10 - £15. Is there really any justification for this large price range? I can appreciate that some valves are more microphonic than others but many claim there are tonal and other subtle differences. Perhaps you could make a short video either debunking or confirming the facts on this sensitive issue. Keep up the good work and excellent content.
Thank you for your input Sharkey. The video would be great. I'm not so sure if people can handle the truth when it comes to this question. I find many want to believe in magic. The video would be controversial, that's for sure.
Hi Paul. Yes I am sure it would be controversial, my belief is that one strong tube sounds the same as another but I don't have "magic" ears like some.
Perhaps you could do a video specifically about matching valves, why and where it is important. ie phase splitters, stereo gain stages and outputs.
I have valve hifi amps but rarely use matched valves in anything but the output stage. I am interested to know what matching tolerances are acceptable especially in phase splitter circuit. Perhaps a demo illustrating the circuit with mismatched tubes vs matched and the problems if any that arise from mismatched tubes. Which characteristics are matched by vendors, ie. In the past I have bought GrooveTubes EL34s in matched quads. GrooveTubes claim to match their tubes for gain AND distortion, How is this achieved, is it just marketing.
You make things very clear and very understandable to folks like me. I don't know much about electronics but this was fascinating. Thanks for not talking "above" me.
I find myself more and more these days, in a state of awe and wonderment. The fact that resources like this exist, of a quality and depth that would have been unthinkable just a few years ago, for nearly anyone and everyone’s benefit...seriously, what a friggin’ time to be alive!I’ve got to remember not to take it all for granted more often.
I’m light years from being considered a professionally competent engineer. My career certainly has a heavy technical aspect to it, but I also have just an insatiable curiosity when it comes to understanding the world around me.
Thank you for sharing your knowledge.
Thank you for making these videos.
Their value, to me, is inestimable.
I know right?
I don't have a ton of cash so I try to spend what little patreon money I have on people I feel really make a difference. As soon as I saw the first couple of videos I jumped on his patreon.
Paul is amazing, super easy to follow, incredibly thorough and the test equipment that you build in his course are almost beyond belief in their abilities, especially the SIFT capacitor tester / Prognosticator and the Super Probe.
I'm like you and far from being anything more than a Simple hobbyist. These videos and the test gear that you build have me much closer to the "Somewhat Advanced but not a pro" Level...
The resource that is amazing and beyond belief is Mr. Carlson himself. Everything you see around you was once a thought in someones or somethings mind, even the stuff not man made.
I concur.
You are so correct sir. I got really serious about electronics troubleshooting around 1999 or so. I was about 17. I used a lot of Internet newsgroups back then. It wasn't great all the time, but now, it's just amazing what we can do and learn. The funny thing is when I wanted to start learning about repairing power supplies and things like stereos and tvs, everyone said I was wasting my time, that nothing is worth fixing anymore, etc. I didn't listen to anyone. I did what I wanted to do and i'm happy with that. I got such tremendous pleasure out of fixing an old 14" CRT monitor then, and I still do to this day. I don't regret my choice at all. This channel and Mr. Carlson help me get better at this, and i'm grateful to him for that.
Haha the battle between musicians and technicians...awesome. Good explanation with the load issue. I had a Boogie Dual Rectifier on the bench once and some guy had stepped over the speaker cable on stage at full power disconnecting the speaker from the amp. The plate voltage sparked into the heater as it is the closest thing to it and evaporated the metal clips in that socket completely. After replacing the socket luckily the amp worked fine but this could have been a total blow of the complete amp easily. I wonder why manufacturers are not putting over voltage protection into there amps. I use 2x 1N4007 in series reverse at the plates to ground which gives me a 2kV protection and if these blow it is much cheaper then everything else that is in an amp. Another great video and awesome stuff on Patreon!
A coupla rect. diodes ay? That sounds like a very good idea pentode!
Also, a 100 ohm, say 10 Watt resistor soldered across the speaker terminals inside the chassis would provide additional protection.
15:58 props for mentioning 'doghouse' cap can cover. A lot of times they cannot even be there, making for interesting times for hands checking out the speaker connections, or pulling the chassis as the output transformer is right there and a go to for leverage. The last high-powered UL pro I was in which is almost exactly like that 70's twin you have had 525 on plates, and although it was functioning well, one of the electrolytic under the dog house had intermittent connection so free to charge I would imagine. Pretty sure that design uses two 350V 220uF in series for 110 + - at 700V... Lately I've been reading people's know-it-all Stance that there's not enough electricity (current) to kill you... I invite them to give a lick to the guts, or would they allow their kids, or pets to play in there. Heck I washed my car and touched the auto garage door track and shocked the hell out of me.
wish i knew 1/10000th of what u know.. love the vids.
This is great !!.............Thank you !...will go check your Patreon !
See you there!
Great instructional video. thanks!
Hi Paul, I did some checking with a 10uF e-cap in parallel with a 10K resister, and my Peak Atlas LCR45 tested the cap better than my Brymen, Fluke, and other meters. I didn't expect that.
Very interesting idea
Awesome! Fascinating!
Factually, "vibrato" is a change in pitch, "tremolo" is a change in level (volume).
U should make a twitch channel!!!
I NEVER understood Fender's upside-down tube orientation!
To save space on the inside
Three years ago this was one of the first tube amplifier video I watched, now I work on amps for a local shop and my own customers.
oof
Was an owner/operator of an electronics repair shop, did warranty and non-warranty repairs for some major manufacturers of radio/tv for almost 40 years. I still learn from watching the workflow of others. Enjoy your videos... loved the Hammerlund restorations. Keep up the great work... Rich
You know you are getting old when they start talking about old Fender Amps that are the black tolex. I worked at Fender or at that time CBS Fender Musical Instruments assembling Twin Reverbs and all the others like Quad and Super Sixes. I also assembled all the Speaker Enclosures like the Baseman and Dual Showman. At that time everything was built in the whole plant by piecework another words you were given a standard you had to build in an hour to be equal to your pay. If you built more than that an hour you got a percentage on your hourly pay like a raise. There were like 4 people remember that could that could build at over 200% with zero issues and I was one of them. For instance, a Twin Reverb had a time standard of 9.6 an hour for 100% of of your pay. I could assemble them at 20-21 an hour. So that equaled like over 200% of my hourly pay, which making double your hourly wage was pretty good pay back then. If you did less than 9.6 you still got your regular hourly pay, but you were not going to last long if the company only got that out of you. The only problem was that if you turned in over 200% they would send down the Time Studiers to adjust the standard they really wanted people to only make no more then 150% so us top assemblers would stop working at the 7th hour and just sit around until the shift was over. Boy do I have some great memories of all those guys I worked with and the great times we had together. Glad to see they are still working out there.
Thanks for sharing your story Jeff!
"by piecework another words"?
"were like 4 people"? So they were like people but not actually people? Robots?
GentIlemen, I've been doin tube guitar amp repair for a living since 82. I used to do Fender warranty i n the 90s. I got to know Fender employee,John Fouch. I saw a picture of Nez Pierce leader Chief Joseph from 1890s. The photographer was Johns ancestor.
Jeff thanks so much for Your post, and work. I am sure many of the amps I still see alive and Kick'in ass are the result of Your work ! Fenders are my favorite amps to work on!
Jeff Hook, what you describe is exactly how management operates when I did machining for an aerospace and aeronautics company. If you found a way to beat the time standard, you dare not beat it by too much because you wouldn't get a raise or a bonus; you ---- and everyone else --- would then be expected to make those "extra" parts each and every time!
I have been working on electronic equipment for several years now and have even taught a rather condensed and relatively advanced electronics course recently. I must say that I've always loved my field as a total science nut, however finding Mr. Carlson's videos has changed everything for me. I didn't expect to find someone so in touch with this world of electronics. This is either formal training as an instructor or the greatest naturally talented instructor I've ever seen, and I've met many great professors and teachers. Mr. Carlson has turned my profession into more of a passion than ever before. Watching Mr. Carlson work is a very humbling experience for me as it shows how much there is to learn as well as how exciting electronics can be!
I'm here as a musician that uses tube electronics that is quite interested in them, except I usually sit right around 40 to 150 hz, as a bassist. It's funny you say that about the master volume twin reverb, Fender actually made them less prone to distortion(not that a regular 85 watt Twin is pleasurable to be around at that volume), I had read that it was due to a shift to ultralinear output transformers. I've never been able to drive a UL 70s Fender amp to the point of overdrive that wasn't painful to be in the same building with. Even as a bass player, running my 8 ohm UL Studio Bass(200w, "enough") into a 4 ohm load it was still hearing damage volume at power tube breakup. Incredible amps, these are.
I've learned so much over the last two days watching your videos about tube electronics, easily the best electronics videos on the internet.
You, along with Uncle Doug, DLabs and The Guitologist, are by far some of the best channels on youtube for troubleshooting vintage gear.
Props to all of you.
Invaluable information.
Smithii I second that
I am gonna check those out, I would also add.
EEVblog, Louis Rossman, Ave, this old Tony and Electroboom for some high voltage comedy.
Thanks so much for including me in your list of preferred channels, S :)
@@UncleDoug Who are you uncle Doug?
I will check you out.
Hi @@UncleDoug I just watched your current limiter protection video and I have one question. What does it matter the black wire or the white wire for the bulb? I thought AC was AC and both sides were in effect the same?
electricity is fascinating and channels like yours and electroboom make things simple enough for an ignoramus like me to understand. Thanks for teaching mate.
New subscriber
What an enlightening video!
I was hooked as if I was watching a good detective film. An hour and six minutes flew by in no time.
Please make one about a solid state circuit.
Your warning about high voltages reminded me of a time in High School Electronics class when we were dissassembling old computer monitors. One student was gone when the teacher explained how to properly discharge the tube capacitor. There he was taking the monitor apart. We asked him if he discharged the tube. He looked confused. We explained the high voltages inside. He carefully put his screwdriver down and slowly backed away from the workbench.
Hah, that's... a surprisingly sober and proper reaction. ;)
Your channel has quickly become my new favorite. So much knowledge and such a good teacher. Lesson #1: RE-CAP EVERYTHING. I've learned so much about capacitor failure from watching your videos. Keep it up Mr. Carlson, you're awesome!
Thanks Nicholas!
Like the butler, the capacitor is nearly always guilty.
At 32:27 or so, you tell us how to explain to a customer how we need to replace the wax caps for the amp to be dependable. All it takes is one customer to tell you, "You've destroyed my sound!!" and you realize that another tactic can be added to placate them before you start replacing caps.
Basically, what I do is draw a small trapezoid (triangle on its side) on the left side of a piece of paper, and a larger one on the right. Then I tell them that the trapezoid on the left represents the guitar input, and the one of the right is the output. Next, I tell them that what we want is for the output to be an exact copy of the input, which means that the amplification chain has to be very linear for this to take place. "If you want to have a particular tone, the best place to insert this tone is before the input of the audio amplification chain."
I then explain the use of guitar pedals. "They are distorting the audio signal of the guitar; however, what is important to note here is that the audio-amplification chain will duplicate this signal exactly, as it's a linear amplifier, and if I don't replace those wax capacitors, it won't be able to amplify in a linear fashion. I will show you how to duplicate your tone, once we have the amplifier working correctly and safely. I also tell them about possibly destroying the amp, as you do, Paul, for added impact :D. Another thing you can do is go here to UA-cam and show them what happens visually to improperly-biased tubes. One good red-plating video speaks 1000 words :D.
I've often thought about injecting a two-tone signal into the amp and displaying the output on a scope of their amplifier in a before-after analysis, but I haven't had a reason to get this far -- AHEM! -- yet :D. That day will come soon -- I'm sure of it!
Another thing I do is explain the reason we want to use high-quality electrolytic capacitors in audio circuits. Some might say this is overkill in a guitar amplifier. Maybe. OTOH, when I tell them that this amp will sound so good that you could also use it for semi-decent HiFi audio on their computer or home entertainment systems -- although it will increase the repair cost a bit -- I get an instant "Do it!" from them, and all is good :D. Should any of them doubt this, that's when I turn on my Deluxe Reverb and play a song they are very familiar with, folks. That seals the deal completely, and from that point on, you are thought of as the local amp guru, even if you deserve that moniker or not :D.
It's all about the marketing, especially with people you don't know. Show them things visually and teach them verbally, because this is how most people have been taught to learn. It's also the reason UA-cam is such a great resource for learning as well.
73...
HF500?
@@domi7007 I take it you're talking about the amplifier for ham radio, as in the LDMOS amplifier? Haven't played around with LDMOS just yet. Too busy fixing guitar amplifiers and old tube radios for my collection. A lot of folks are learning to play guitar during the coof, and that industry is booming.
Here's an interesting aside. I watched a video from Premier Guitar on Brain May's setup that he uses while playing. He uses an old VOX amplifier, and he removed the negative feedback so his amp distorts easier. Doing my homework on audio amplification, I've found out that this would allow him to use fewer pedals, and the more pedals you use, the more noise is introduced via amplification.
Personally, I'd never go this way. One would think that doing so would be a bit harder on the tubes in the audio-amplification chain in the final, but now I'm not so sure that my original assertion is totally correct. LOL!
OTOH, it is my belief that A.I. is going to completely change audio amplification, and it has already done so, via something known as "modeling amplifiers." I'll step out on a limb here and say that all new amps will be modeling amplifiers, in the not-too-distant future, and pedals will be a thing of the past, although I'm sure will still see a ton of purist.
Oh, I joined your Patreon, Paul. Love your inventions and projects!!
@@davehebert3403 A I will only work in guitar amps if you've got a computer in them.
It would be nice to see a Part 2 of this video testing the Electrolytic Capacitors and replacing them, Testing the Output tubes and looking for matched pairs and also Biasing the amplifier.
Thanks
Betcha he does just that!
The Bob Ross of electrical and electronic videos. Calm, exceptionally knowledgeable, very well produced videos. Nicely done, Mr. Carlson.
Thanks Jim!
I signed up today for Mr Carlson's Lab Patreon $20 per month option because need to support quality videos like these - Very Well Done!! I look forward to learning more on your Patreon area.
I worked as business equipment engineer for many years and I used to service automatic bank dictation equipment I.e. connected to telephone exchanges. The GPO engineer at the exchange told me the painters were in to brighten up the rooms around the equipment. There was racks of lead acid batteries all connected in parallel for power backup if the mains failed! they remarked “it’s safe enough as the total voltage is only 50 volts! They forgot to mention that the total current available was massive (several thousands of amps) There was a huge bang when somebody dropped an aluminium ladder among the terminals and part of the ladder simply melted! Lucky nobody was injured! H S wasn’t very strict in these days! Fraser
Thanks for sharing your story!
It is a pleasure being part of your Patreon and I appreciate all the knowledge and skill you have shared with so many! Excellent channel and work!
Old ground based aircraft navigation transmitters had 250 VDC as low voltage, 750 VDC as medium voltage, and 12,000 VDC as the high voltage with plenty of current. You paid attention really well when you did anything at all, anywhere.
Got a Twin Reverb like this sitting across the room from me that I bought in 1976 except it's an earlier 100w not 135w. Had it modified with a Rivera/Boogie sort of lead channel and used it from Egypt to Japan and points between back in my traveling days. Briefly had a 70w Pro Reverb which should be nearly identical to this Twin Reverb except half power. Now mostly use one or two of my other amps (69 100w plexi. 79 50w Marshall, 68 Bandmaster, a couple of newer Ac30 types) these days. I don't have as many amps as some folks but love them all, especially my Twin Reverb because it was my first REAL amplifier. Great to see Mr. Carlson feature this Twin Reverb amongst the vast array of gear he deals with.
On that kind of old amplifier, you cannot keep everything original more than about 20 years. Just because the capacitors don't last forever, especially the electrolytic ones. Same thing for the carbon resistors, they tend to become very noisy and unstable. You'll never get the original sound as it comes from the factory, just because component values tend to change through the years. If you prefer noisy stock amplifiers, it's your problem!
Thanks Paul, what a great way to spend my morning while I should be working :)
getting zapped inside them only hurts a little bit, before you die ;)
Hi Mr. Carlson, I just wanted to say thank you and tell you that your Patreon program has been so informative and valuable to me. It has not only taught the fundamentals of electronic repair but given me and the rest of your patrons the information and even the tools to troubleshoot the circuitry all the way down to the component level. It’s been an amazing bit of information and I can see why so many are joining up. In addition to learning, it’s been a lot of fun and I look forward to every new video. When I saw this video today, it reminded me of that. I know that this isn’t as easy as it looks, you don’t just sit down and knock out these videos, it’s a lot of work. Like I said earlier, I just wanted to say thank you, I’m having a great time! -Buddy
Thanks for your kind comment Buddy! Lots of sleepless night go into these video's. I'm beginning to think, the lack of sleep is "video fuel."
I agree. I became a Patreon months before I planned on starting to build anything because I knew that the information, projects, and teaching was worth much more than what I had to pay to be a member of Paul's Patreon channel. Thanks Paul!! You're the greatest!
What is sleep but a waste of life, sleep less, power nap and get more done, including enjoyment, life's too short, a couple of years ago I was 28.... now I'm 62 OMG where has it gone????
😢started learning electronics in the mid 70s from a tv repair man who was also an electrical engineer also tought me math that i could never grasp in school learned mor in 3months of working with him then i did the entire time in school you remind me much of him in my 60s now cant see for sheit but love whatching your videos makes me really miss my electronics
Thank you Paul for sharing this Patron video, because of it, I was made aware of snubbers in a bridge rectifier, then doing some research, learned of their value.
Cheers,
Adriel
I translate musician terms to engineering terms. What they talk about most is "tone." That refers to the overall characteristic sound of an amp. They aren't crazy, and they aren't really being picky. They have a sound that they like and they want to retain that. The plate resistors may have increased in value, and increased headroom. If they like that, you need to either install a corresponding current value of metal or carbon film resistor or just leave it alone. The original may read 120K instead of the marked 100K. But with caps, leakage is the worst thing.
This video was an excellent campaign to the morning coffee.
BOY you are the tech EVERYONE WANTS....methodical...thorough....detailed.....you're TERRIFIC.
VERY experienced. So great....THANKS Paul....(UNCLE DOUG....TWO OR THREE others.... such good tutorials.). Perfect for me. Your a GIFT really. Thanks again!
uncle doug doesnt even know how to wire safety grounds properly. Id recommend psionic audio and brad's guitar garage for other experienced amp techs
4:29 - ALWAYS take the user's 'diagnosis' with MANY grains of salt!
Also, I can't help but wonder if it does turn out that all the electrolytics are original and the cost of replacing them would exceed the claint's budget, does he just take the amp to the dump? That would be a real waste!
Include grains of salt when accepting another tech's word. They can be wrong too.
If the customer doesn't want to pay for new caps in an old amp they're bloody crazy! "Here's your $2000 amp back that you don't want to spend 2 or 300 dollars on. Now piss off & take it to some dodgy tech you halfwit!"
"As hot as the blazes of hell"
And the hotter they get the better they sound! Right up until they break down. I've seen black goo oozing out of transformers (melting the potting compound) at midnight in a crowded venue. Man those amps sounded great! There's something about pushing them past their advisable operating limits that makes it all sing (until they break down).
One problem that I saw when fixing Fender amps took me years to finally get to the bottom of. Several Fender amps that I saw would have random "shot noise" that sometimes sounded like lightning interference on an AM radio, sometimes it had random whistles and squeals mixed in. I traced the noises to something in the interstage coupling circuitry. If I squirted the fishpaper and eyelet "circuit board" that Fender used with contact cleaner, the symptom would go away for a while, but would reappear once the cleaner evaporated entirely. Yes, I was mindful of the high voltages while doing that. The few times that I fixed it, I ended up removing certain tie points from the paper and letting the connection float in the air. I learned years later when working with other equipment with high impedance/high voltage connections that after the passage of decades, solder rosin flux residue becomes a noisy resistor. I now know that the original removal of the flux at the Fender factory had driven a small amount of flux into the paper which years later would cause the noises we heard.
Wow that's interesting Dobbin! I thought you were gonna say something about leaking electrolyte from a capacitor making the cardboard or elephanthide rivet panel conductive! But flux doing that? I'd never have thought.
For such a seemingly young fellow, you seem to have knowledge way beyond your years. Most thorough and comprehensive videos I've ever watched, and they are great.
Yes maybe worked with an old timer ?
That's exactly my thoughts.
Hello Paul, have you ever thought of doing a video on how to add adjustable bias on the various fixed bias design tube amps?
That would be a good topic. Thanks for your input Mike.
Thank you so much Paul. I have watched many, many videos on tube amp servicing and followed along sort of understanding what was being said but the way you explained each step finally made the light come on. (No pun intended). I hope you do more.
Paul. Those .01µF ceramic capacitors are long lived. But, I very often replace them with poly caps, because they tend to be highly microphonic.
Hi Ken, you are very correct about the microphonic aspect of ceramic capacitors. If they are used for bypass, and are not in the audio chain (or have been chosen for a specific quality) it's ok to leave them in circuit.
Yes. I should have said that I replace only the ones in the signal path. And, only if they are particularly microphonic. Otherwise, there is no need to replace them. Cheers!
It is always good of you to issue the warning about HIGH VOLTAGE. One time, as a young teen, I had a Motorola 2m VHF radio powered up. Managed to get the b+ across the chest and that really, really smarted. Worst shock I took. Of course, tube gear was the only readily available hobby material in the mid 60's. I did take a number of shocks and drew many sparks. I never got use to either. Later on, I learned to keep my left hand in my back pocket when probing live circuits. For those new to these circuits, make sure your scope probes can take the high voltage as some cannot. Keep the ground clip on ground.
I MY SELF have built a Marshall 18 watt amp . and also a fender champ 5f1 with my brother. 12 ax7 6v6 I like el 84s tube amps are great. have had a line 6 dig 75 watt spyder 4. Thank you Mr carlson for your great videos.
God bless you, you are the best, Your posts are a treasure to whoever wants to learn, thank you millions
You are very welcome!
Love your videos. However, it makes me cringe to watch you point at live circuitry with your fingers so close to high voltage. Maybe it would be safer to use a non-conductive pointer and keep that second hand away from the chassis. Am I wrong in my assessment? I admit it terrifies me to think of working on a live chassis, or even one that might have residual charge in its caps.
18:08 Nice pun... removing the 'cap' from the caps.. In the Fender amp world, this is often called the 'doghouse'.
You should show folks how to make and use a dim bulb current limiter. It will save your life. :) Not hard to make.
"This the kind of stuff guitar guys are looking for." Yea man.
Great stuff man, you're with no doubt one of the best and most useful channels, keep it up, you're great.
The standby switch disconnects the caps in the capacitor tank from the bridge rectifier, so discharge them at the low end (away from the rectifier) of the standby switch for safety before sticking your fingers in there!
You are the BEST on UA-cam
New subscriber here. Love your videos!
I was working on a 1976 Fender Vibrolux about a year ago for a friend (similar vintage, but smaller amp with roughly 40 watts output, if I recall). I have another friend with the knowledge and test equipment who went through the chassis for me. I was mostly taking it apart and cleaning 40 some years of filth out of the thing. Other than replacing the tubes and cleaning some crackly pots myself, after he was done, my work was mostly a cosmetic restoration. Got it back together, plugged my guitar in, and it sounded great! Just like new! Returned it to my friend. He loves it!
There was one step I found later that we had not addressed, wherein lies my question: adjusting the bias. There is a small nylon screw on the tube side of the chassis which was on or near one of the transformers. The Vibrolux, being smaller, is only powered by 2 6L6s, hence one bias adjuster screw. I believe the Twin, as it has 4 6L6s, has 2 of these bias adjustment screws. Could you do a follow up video, once your amp is back together and running, explaining the importance and/or procedure to this process? Another music/ gear-head friend of mine said that bias adjustment is important and I should get the amp back and have this done. I did go to the trouble of buying a matched pair of 6L6s, but think that bias adjustment may still be necessary. Would love to hear your thoughts on this!
I've been working on the "CBS" Fenders since the time they were new, and the black face Fenders since the time they were 1st released. Yes on the high flying filament wires. The black faced Fenders had cloth covered solid core wire that took a higher tight twist so they tend to be less hummy. Yes the 'blue molded" poly caps almost never fail.,and yes the mallory filter caps usually have to be replaced, even though often times they "still work",.. the electrolytes dry out. The one error in design seems to be the tremolo cap that You reference at 45:12. since the tremolo circuit tends to oscillate between a cathode follower and a common cathode mode, that cap sees way more than the 25 volts it is rated for, although the current is really low. I usually replace them with a small 200-400 V electrolytics that are now readily available. 10-22 UF. The Fenders are set up to play the output into a shorting speaker jack, when the speaker is not plugged in, which is much better than leaving the xformer open. I ALWAYS plug in a resistor dummy load with a speaker divided off that load, so I can see what is going on, looking at the signal across the load resistor.. Silver face Fenders often suffer from parasitic oscillation resulting from a change to the circuit (by CBS) with the bright switch wired so that the 250 pf cap sees a resistor to ground, creating creating 360 degrees of phase shift at some high freq (20-100Khz). That resistor, though not in any schematic I've seen, is hidden behind the brite switch and a bunch of wires. remove it! Silver face Fenders have a lot of problems created by the "hiFi" engineers from CBS. However the Transformers are better quality, but not necessarily to many guitarists taste. The bias balance control is not as good as a bias control for instance. Nice to see and hear Your excellent analysis , that brings up some things i seldom think about.
You got me. I love Fender amps but the 135 watt Twin has around 500 volts on the B plus.They arc power switchs and tube sockets,they are "anvil in the forehead loud".Now that I got that out,all new Sprague electrolytics,new JJ 6L6s,new Tungsol 12AX7s,new EH 12ATs.Better yet sell it and buy a Deluxe Reverb.
29:20 - The output stage is basically an AC current source. With no load, you get a *major* voltage-rise if you were to crank it up! The output transformer would arc and inter-winding insulation would melt!
Very nice, can you recommend an easy to use, cheap scope?
"Don't replace the bumblebee capacitors! They are vintage and sound better as they age! The new ones are fake and don't sound as good!" - I hope you like your blown amp in a few months then.
vintage sound till natural death!
Well Brian radiotvphononut hates those Bumblebees.
I feel you have a lot to contribute to people wanting to better themselves in the field. Maybe you could do so with about half the words? I mean, if someone is watching this to figure out how to fix their amp, and they really need a in-depth explanation of how capacitors work, they're probably a bit in over their heads.
One thing I would add when probing around with an AC coupled scope probe, dealing with wide voltage swings on valve equipment, is that when moving to different parts of the cct, always ground the probe to discharge the DC stored in the coupling capacitor in the scope. Not so important with an all valve set, but if you were to put the probe onto a OP amp or transistor after you have been looking at an anode of something, a few hundred volts could cause an unhappy weekend.
Those are words of experience Seth!
You are of course using the recommended x10 probe with its 10MOhm impedance...etc..
I think it's best to do that after every measurement tubes or otherwise unless you are going right back to the same point in the circuit. It's actually a very easy habit to get into just like when you take high voltage measurements or are probing a high current environment always position your probe so that if it slips off the connection it does so in such a way as it doesn't short anything out. It's all in the way you apply touch pressure to your probe connection.
Aaaargggh! Don't worry about it. Most coupling caps will not be rated much over 50v, because most scope inputs can't withstand high voltages (not designed to). This is why you have a x10 probe, (also for bandwidth of course), to extend your vertical range. The probe has an average 10 million ohm impedance. Nothing is going to happen here - never has to me, and shouldn't to anyone else. Certainly there will never be 500 volts sitting on that cap...The probes are cat rated - or should be - and will be rated to a certain voltage.
@@martinda7446 I don't want to be looking at what's on a plate in an intermittent circuit and then just stab at the next grid and send a spike all the way down stream possibly "healing" the problem.
Excellent, I appreciate all the tech tips. Had a Fender Twin Reverb back in the 70; this thing eats speakers, as they were not matched for the power of what this amp can output. Also, the Reverb circuits are not too reliable. Otherwise, it's a lovely amp. The high voltage warning cannot be overemphasized.
It's funny, your title is like the old tech magazine covers
This was excellent! The way you pointed out the signal path in the chassis and how that corresponds to the schematic was what I've needed to know. I've watched others explain about the circuitry, but nothing comes close to this.
Mr Carlson, I love it.Fender amps even of this era are like working on an old muscle car .I've owned my share of them my friends play them .They are the sound of rock,jazz,blues and American music in general.
this guy is the best viewing i have ever ever ever seen...he is an amazing person.
Totally amazing. And I don't even work with tubes. But there are so much other to learn from your videos.
Instead of talking about how to open the device, why aren't you showing it? It's a video after all.
one that you're supposed to pay for too lol
AcceleratingUniverse I would not say that only for-sale videos deserve attention in the making. But as you are speaking about paying: are you aware hat we actually pay for these videos?
@@christiangeiselmann No chance buddy I adblock everything
Guitar players pay big money for vintage, “classic” tone that modern electronic components (resistors and caps) - even with vacuum tubes - don’t reproduce. That’s why these guys are super touchy about what you replace and what you replace them with.
Hi Joe. I guess what isn't understood is: The amplifier parts are degrading now, and only now do they sound like that, (classic sound.) After the amplifier is rebuilt, it would sound closer too the way it did "from the factory" when it was released. Whats even more interesting is: People don't realize the magic is in them, not the amplifier.
You never fail to amaze me with your info and teaching ability, Thank you. Beings that I am a T-shirt junkie, have you thought about any advertisement bits, coffee mugs, T-shirts, just some odd and weird stuff that has your logo and channel name printed upon them... Try a small batch of test T-shirts, let the fan base know this is just a test run, of only 50 , just to see if this avenue is worth the effort on your behalf to deal with, setting up, like your time isn't already consumed, but, I would buy a T-shirt and where it proudly
Thanks for the insight Dru, I will consider merchandising in the future.
Your teaching is a generous gift Mr. Carlson. Even at 70 I'm playing and learning. Thanks.
You're very Welcome!
Glad I found these videos, very thorough. Each one yields a wheelbarrow of knowledge. Keep up the good work. You are my new hero Thank you!
Wow, that was incredibly educational. I have learned so much in this video. Thank you very much.
Thought it might be worth adding that when testing transistor or valve amps, there are different considerations as to loading the speaker output.
With a transistor amp it's generally quite OK to run it with no speaker or dummy load connected, even at reasonably high signal levels. The thing that will damage a transistor amp is a short on the output, and the damage can occur literally in milliseconds. Transistors can pass high currents because they have inherently a very low internal resistance. Even if the amp still works after the short, it may have been damaged and pack-up a while later.
Since many such amps are DC-coupled, an output short with no signal can still do damage. As can shorting the output soon after de-powering if the supply caps are still charged.
A problem can arise here with certain 1/4" jacks and jack sockets, where the jack tip can ground-down momentarily as it's put in or pulled out. The momentary short this creates can do damage. A Speakon or XLR connector is preferable.
Somee people imagine that the fuse will save the output transistors. It will not. The fuse is there to prevent a fire.
On stereo amps, never parallel the two channels to the same speaker. This is effectively the same as shorting both outputs, and is very likely to do damage.
Some of the more powerful units have bridge outputs, on which both sides of the speaker have signal voltages. Therefore, never assume that you can safely ground either terminal of the speaker, for example with a scope probe shield.
A further concern is that a fault in a sold state amp can destroy the speaker by putting DC onto it. Therefore, either use a speaker you can afford to lose, or test with a series resistor (say 100 ohms) to limit the current.
With a vacuum tube amp, it's a rather different situation. Tubes have a high internal resistance, so the short-circuit current is inherently limited. An output short will generally do no damage so long as it's not sustained long enough to get the anodes red hot. Running the amp with no load at high volume though, will cause abnormally high voltages on the output transformer and tube sockets, and may cause a flashover. This is even more so if there is a faulty connection in the speaker wiring which makes and breaks. (That output transformer is basically a car ignition coil on steroids, and it will want to produce a spark if the circuit is suddenly interrupted.)
I would always take a close look at the output tube sockets, and replace any that show tracking marks around the anode pins to any nearby ground. This is usually a sign that the have arced in the past, and once the insulation is weakened they may do so again.
So, test solid state amps either unloaded or with a dummy load, but be especially careful to avoid shorts. Test vacuum tube amps with a dummy load, and beware of bad connections. In either case the dummy load need not be exactly the speaker impedance, somewhat higher resistance is better than lower though. A series resistor for your test speaker is also a useful addition, allows monitoring at low volume, and won't pass enough DC from a faulty amp to burn your speaker out.
HTH. These video bring back fond memories of my time on the audio bench. In some ways more rewarding (and less frustrating!) work than maintaining computers.
Oh, and do heed the safety warnings. They are not exaggerated. There are some truly evil voltages in guitar amps.
This rings true. It's easy enough just to put an eight(ish) ohm resistor across the output whether it's a tube or solid state amp.
@@micametalgem3721 Hi mica. I agree. Much safer to connect at least a 100 ohm or less resistor across the speaker terminals just in case. You may accidentally cause a 'blurt' by touching a test probe onto a grid with your finger touching it (hopefully not!), or something similar. This 'blurt' may be enough to damage the amp. I don't think it's worth risking a $2000 amp by simply not connecting a resistor across the speaker terminals, especially if it's someone elses amp!
Best video, ever. (And I'm a guitar player.)
Thanks for putting in you time to make this video.
Excellent as always. I am trying to fix a modern mixer P.A. that is mostly SMD. Needed some Carlson therapy to stay sane!
Thanks so much for sharing this video with the general public.
Your instructional videos are the finest I've seen on UA-cam. Thank you.
How do you manage to find schematics for these circuits ?
Your a genius Mr.Carlson, I love your channel and ability to educate the general audience, for me anyways.
Thanks for sharing!
Kind regards Eric Dee
I seriously enjoyed your video and learn something from your video. Thanks so much for making those excellent video.
I always smile when Paul says: "bad things happen..." because we all know what it means in electronics...
You use ge silicone II, too. I use it for heat shielding especially on induction coils. I put about 1/2” layers on them.. I’ve gotten inverters , high power drivers, fet’s etc to last for years using this method.
Very much enjoyed this video. Your skills far outweigh mine and that comes from learning and experience, something I hope to also acquire more of with the boost from your excellent presentations.
73's de N9ZN - Tampa Fl.
Thanks for this video. It helped me as I worked on an older Crate Blue Voodoo 6212 combo amp. Your videos are extremely good for building confidence in the repair process. Thank you!
You're welcome Mike!
You are so kind...such a talented man......you really know how to teach.....God bless you....
41:22 - Beware those poly style caps! Some of them see a high DC voltage. These should be checked!
I want to thank you for reteaching me electronics. Please keep on making more videos as so to benefit a lot of the newbees who have consent to go down this wonderful road of discovery.
You're welcome Mr Victory.
You have the best videos ... Outstanding information!! WELL DONE!! Would enjoy to see a video sometime with your outstanding detail to know how to get that buzz/vibration out of Treadmill type DC Motors when they are under load ... Capacitors vs. Choke (Coil) ? ... seems to be a common issue with MC-60 Variable Speed DC Motor Controller using a 5K potentiometer ... I can put my DC Power Supply from my workshop to run my Treadmill motor and it is silent ... but with the MC-60 board it needs something to smooth out the DC power from the Bridge-Rectifier ... Thank You again for making your videos.
LOL, I know that simply because the video is posted, all is well but every time you point to a component in a live circuit I cringe. I also understand the foreshortening the video camera has but, ........ still, ..... it creeps me out :P AGAIN, another excellent video. Thank you!!!!
20:10 when I worked at an auto parts store, and a customer came in with a part, from a reputable manufacturer that did not last as long as it should have, I would say, "one day someone sneezed on the production line and part just won't last as long". You can make the best parts in the world, but you can't defeat statistics. *someone* has to get a bad part sometime. A mote of dust in a switch, greasy fingerprints on some solder joints, a worker had an argument with their spouse; the best factory in the world can't control all of that. If the company has a good reputation, and they make it right, you might want to give them a break.
Thank you for this video! I am finally getting back into electronics. It is finally time to see what the heck I messed up with my guitar amp build I did way back around 2008. I was young and while I learned a lot, it wasn't nearly enough.
I just hope I don't end up spending a lot on more components. I easily spent $300 or more on parts alone for one of the most simple tube amps ever.
Wish you pronounced the word Chassis correctly. Ch is pronounced SH . SO THE WORD IS “SHASSY” it’s root is French.
Just love your videos Mr. Carlson. Thanks for suck excellent quality presentations. Your up there in my top ten UA-cam presenters.
This is great, it brings me back 50 years