Two Types of Tube Amplifier Hum and How to Determine the Source

[@UncleDoug]

PLEASE NOTE: I posted this video primarily to assist in determining if the hum was created in the power supply (120Hz) or elsewhere in the circuit (60Hz). A faulty tube can cause the 60Hz hum, as in this video, but there are literally hundreds of other possible causes. Indeed, there are internet sites that offer helpful lists of these possible causes. Please consult them if you have ruled out the power supply or a tube as the cause of the hum in your circuit. Good luck.

[@donh01965]

Would that make the tube unusable in every application? Could it be usable in say test equipment or other non amplifier items?

[@Angelum_Band]

I would like to thank you for your explanation it made so much sense and resolved my problem. BTW 61.74Hz is a low B so if hear a flat B in your spectrometer ap you know where it's at.

[@fuzzyhi5621]

Where you located I was wondering if I could send you an amp to fix?

[@UncleDoug]

@@fuzzyhi5621 Please message me at my FB page: Uncle Doug's Vintage Amps.

[@RiotHomeRecording]

@@UncleDoug What about buzzing? Is that a tube thing or more of a grounding issue in your experience.

[@TheOldOakSyndicate]

You got some of the best "How To/Electronic Amplification" videos on KZbin! Keep up the good work Uncle Doug!

[@UncleDoug]

Thanks so much, OOS. Rusty and I really appreciate the kind words :) ^. .^

[@wildthing3026]

Uncle Doug I think that you are an amazing technician. ....and a great person to share your knowledge...just love your videos...many many feel just like I do....

[@curtisowens6413]

Absolutely the best!

[@nathanwatrous1519]

This video is a sanity saver. I restore Bogen Amps. I have a challenger cab on my bench right now. I recapped the whole darn thing. After that there was still a 60 hertz buzz. This buzz was present no matter what I did with any of the controls. I noticed if I turned down the voltage on the variac, that the buzz would calm down. So I tried a voltage dropping resistor network on the heater circuit. Didn’t change the buzz. I even ran the heaters off of 6 volt battery to see if that would help. Nothing, still the same. So I did some research and came across this video. So I started pulling tubes, long behold the phase inverter, a 5C4, was the culprit. These tubes are dirt cheap, so I have some on order. Thank you so much Uncle Doug!

[@UncleDoug]

That's great news, Nathan. I'm glad the video was helpful :)

[@MrLespaul1963]

Uncle Doug...thank you for being so informative and helpful. I've been a musician (mostly electric guitar) for 35 years. I've been a gear head and DIYer as long. You've really broadened my understanding by taking what I understood from the theoretical to the practically. See, my day job I'm a pharmacist and have zero formal training in electronics. Everything I know is self taught and its served me well. I've been wanting to build a tube amp from scratch and have hesitated, until now and thanks to you opening up my understanding, I'm ready to take the plunge. I'm looking at the P1 from the AX84 collaborative group. As to this video, as soon as you said it wasn't from the filter caps, my first thought was the heater grid being involved. Your MOA for the heater grid involvement makes perfect sense and I learned that the filter cap AC hum is st 120 Hz...I had never thought about the quality of AC hum from the filter caps being double. I understand the how. The why just had never crossed my mind. Again thank you.

[@UncleDoug]

You're welcome, Kirk. Rusty and I are self-taught also, so we're quite glad to hear that our videos are helping you gain knowledge regarding tube electronics. Best of luck with your amp-building project.

[@allendodd4844]

Your dry humor and Rusty's attitude really make the information more fun. This is one of my favorite youtube channels.

[@UncleDoug]

Wow, thank you, Allen. We appreciate your kind words.

[@russmills5103]

Video made 10 years ago saved me all kinds of time. Had almost the same problem, only difference is mine was effected by the master volume, but identical sound. The very first preamp tube I replaced fixed it. Thanks!

[@UncleDoug]

Glad the video was helpful, Russ :)

[@twirlyboggs]

wow, that helped me confirm what was happening on my amp. I was getting thqt 60 cycle hum on it, and after the 5th preamp tube swap, it's now gone! I may try another online store for my tubes and see if i get quieter ones. I also thought about getting 12ax7WA's too. Your videos ROCK!!!

[@UncleDoug]

Thanks so much, TB. I have chased hum for years, replacing all sorts of components before finally discovering that it was simply a noisy tube (usually a pre-amp tube like a 12AX7). Another strange discovery is that sometimes a tube that hums in one amp is quiet in another.....probably dependent upon which of the two triodes in the 12AX7 is actually noisy. Regardless, the tone of the hum is definitely a great clue to its source. Best of luck !! :))

[@twirlyboggs]

you are truly full of knowledge~ funny u said that about diff amps / same tube, because one of my amps just seems to never have noise after rolling preamp tubes - never really thought about it tho~ i love making thought connections, thanks!

[@UncleDoug]

You're welcome, TB. I guess some circuits are more sensitive to noisy tubes than others. Again, thanks for your great input :))

[@michaelyoung6986]

Epiphany moment💥 I came here after a random unrelated rabbit hole and found an answer I've been looking to understand for years. Thank you.👍

[@UncleDoug]

Glad to hear it, Michael.

[@jeffbeck6501]

Great info. I think dimmers can also cause problems. I have rarely had no hum on my amp. In big clubs in big old buildings downtown with those damn beer signs everywhere, I have had so much hum at times, that one time I pull off the ground to unground the amp to get less noise, as I had to do at home for recording to reduce the hum and it worked well. The only problem was that during my first song of the first gig of a big band that I had joined, playing in front of a full house of 500 plus fans, the singer walked over to me on stage right and put his hand on the back of my neck while he was holding the microphone and SHAZZZZAAM BAM POOF. He just about electrocuted me and I fell back on to the floor. He did not feel the shock, nor did he see me fall backwards onto the stage floor. He went back to the other side of the stage while focusing on his singing while I was half dead trying to hold a first position A chord with one finger the best I could while recovering from the shock. After the singer had walked over to stage left he turned around and saw me, the new guitar player, playing the guitar parts while laying on the floor. He never knew I got shocked. The first thing that popped into his mind was "kind of hamming it up, aren't ya?" was what he was thinking about me. It took me at least 30 seconds to slowly get back up. I never unplugged the ground at a show after that. And in fact, when I sang and played guitar, I would add a jumper from the mic cable ground to my foot pedal ground. I used car jumper cables. Otherwise, your mouth can get shocked really badly while singing. The singer never knew that I had gotten shocked til after the show. But he had a clue because later on toward the end of the show, I was playing a solo with a wah pedal and could not leave my pedalboard, and the singer came back over to touch me on the back of the neck again, and I was shaking me head, no no no no no. He seemed to pick up on that. So it almost happened twice. I would not have survived a second jolt of club power mains. And to add a bit more carnage, in the middle of the show, while running around on stage in the high energy show band, I slipped on a plastic bag left on the stage from some bags of bananas we threw out to the audience. I took a hard fall to that stage. And our hottest dancing girl announces to the audience live that she is leaving the band to boot. What a crazy night.

[@UncleDoug]

Good grief, Jeff, a few more nights like that and you might be better off quitting the music biz while you can still walk away. What a harrowing experience. Yes, I too believe that light dimmers can cause electronic "noise".

[@jeffbeck6501]

Nah, just another day in the office for me.

[@jeffbeck6501]

And it is pretty you replied to my comments. You are perhaps the #1 guy or one of them at what you do. It is really nice the info you share, and how it gets put on to video for forever, and many people for forever can learn from it. I did not know anything about anything until people like you started uploading videos to youtube. My hats off to all people that do that.

[@UncleDoug]

You're welcome, Jeff. I'm glad the videos are helpful and appreciate your nice comments :)

[@1Dcorace]

Do you ever check house power with a simple receptacle tester to see if you have ground? I see some pretty bad house power in older buildings. No ground, reversed polarity, all kinds of good stuff. I carry a APC power conditioner, I'm not sure it's made any more, but that has helped in the worst situations.

[@lennyb783]

Uncle Doug You are like the honey on my peanut butter. I just listen to the fist talk and at 72 years I have been away from school and you make me want to go back. I enjoy the info and want to thank You for your time.

[@UncleDoug]

+Leonard Nixon You're welcome, Leonard, and thanks for the very nice comments. Rusty and I have posted well over 100 videos, so you have lots more to watch. We welcome you and hope you enjoy them :)

[@crunchchannel9391]

I pushed the subscribe button because i dont want any one offended.

[@UncleDoug]

+Rondo McBower Thanks, Rondo. Rusty gets real cranky when he's offended :)

[@frankfinegan425]

Uncle Doug can you do s video of how to choose a driver tube for a given power tube?

[@vicoilsteems9764]

Rondo McBower Trump loves you.

[@lonnieo4676]

me2...

[@iangray7410]

How remarkably brave of you !

[@anthonyvee]

How informative! thank you, i'm 62 years old I wish i had a neighbor like yourself with the knowledge that you possess, so i can learn from the beginning... never too late to learn i believe and videos like yours show how important, exciting and interesting tube technology was and is...thank you and stay well.

[@UncleDoug]

Thanks so much, Anthony. We appreciate your kind words and wish you the very best.

[@hackit25]

I just came across this video trying to figure out the hum in my tube amp. Great info!

[@dallasrode9653]

I should add I am just trying to learn about tube amps in the last few months. I knew I was hooked when I learned that AC and DC cohabitate inside the same circuit. Love this youtube channel, really great simple to understand learning. Thank you very much Uncle Doug!

[@UncleDoug]

You're welcome, Dallas.

[@UncleDoug]

Mick, your question had no reply capability, so I'll answer it here. Whistles are usually due to oscillation. It can be at the input, where there is usually a 50K to 70K resistor between the input and first tube grid to eliminate it (may have failed or be missing), or due to a slightly microphonic tube. While the amp is on, try lightly tapping on each tube with a chopstick to see if the sound appears or changes. Hopefully, this will reveal the source of the sound. Good luck.

[@babybearkill1]

Hey Doug, All glues by JBL are provided by Moyan. I worked for the Australian distributor as the tech and that's what's supplied www.cpmoyen.com Go check em out, they also supply the dope

[@UncleDoug]

Thanks, BBK. This information would probably be more useful under the Speaker Repair video. I'll add your link to that video description.

[@babybearkill1]

It was the most recent post so I popped it here

[@dwightjt]

Yes indeed Uncle Doug Don't guess diagnose. Many year's ago as a pro. Mechanic certified. I saved me and my customer's Money by diagnosis Not guessing. Your a wise ol man. Love your vids. I have learned more from you in tube Electronics than anywhere else or Books. Thanks for sharing The way you do. Dwight.

[@UncleDoug]

Thanks so much, Dwight. We appreciate your kind words.

[@UncleDoug]

Brian R, your comment had no reply capability, so I'll answer here. Does the amp hum with nothing plugged into it? If so, it's the amp. If not, it's probably your cable (try a different one). 1.) If the hum changed when you touched the strings, it would mean that the bridge and strings are not grounded properly. It doesn't, so they must be OK. 2.) If the hum obeys the VC, then its cause is before the VC in the circuit: input jack not making good contact with cable, faulty cable, lots of electrical noise in the room, badly routed wires, noisy pre-amp tube (switch it and see if hum changes). 3.) There is no way to differentiate ground loop hum from other sources of hum. Unless you have changed the wiring within the chassis, then a ground loop would not simply appear. They are usually caused by a fault in the circuitry design, particularly in the way that components are grounded. It would have always hummed.

[@Brobb772]

Thanks for your quick response. 1) Im not sure if its the guitar cable or not, but I'm thinking not likely? I tried with 2 different chords and hum occurs with both - but i guess it could be possible, just seems less likely 2) I've never messed with the tubes before but maybe i could try and start with the pre-amp tubes; and if i get stuck take it in to a repair person -- whats a reasonable price to pay somebody for replacing tubes?? 3) i can't remember if its always hummed or not. it seems like it has, but i can't really remember because when i lived in apartment i played it pretty quiet and not as often. Now i live in a house and can turn it up. So i don't know if its a fault in the amp design or not. 4) The house from the 60's and its possible the wiring isn't good in the house, and there are a few street lamps down the street that have a hum to them (a couple hundred feet away?), but i dont know what i would do about that..? Theres something online called an Ebtech Hum exterminator ($50 - $75) that plugs into the outlet, but i dont if that addresses my problem or not. Do you know what problem this product addresses?

[@UncleDoug]

You might be better off just taking it to an amp tech and get his opinion on the nature and source of the hum. In some tube amps, slight hum is a normal occurrence. It would probably end up costing less money, time, and frustration to get it checked out by an expert.

[@georgeonerato575]

Thanks Doug. Fixed my issue on a preamp without driving myself crazy. Your the man

[@UncleDoug]

That's good to hear, George. Thanks :)

[@djfrank59]

Once again, you and David have the best videos out here! If I ever get the incentive to clean up and organize my shop, I'll make some tech videos as well, what stops me from cleaning up the shop is, I may not be able to find anything then :)

[@UncleDoug]

Thanks, Frank.....and sometimes you find the missing item you lost back in 2008 :)))

[@djfrank59]

I probably order things I already have (LOL) :)

[@UncleDoug]

....and when I find them, I mistakenly think that the order has arrived :)

[@jeremyb2108]

Thank you so much for making this video. You just saved me $120 for my local amp repair shop just to look at it. Let alone providing me an answer.

[@UncleDoug]

You're welcome, AJ. It's great to hear that the videos offered practical, helpful information.

[@professorhardknock]

Rusty looks like a Norwegian Elkhound. Great dogs.

[@UncleDoug]

We're not sure about his true origin, Prof. His Australian accent made us think he was a Queensland Blue Heeler, but he loves to ski, so Norway is possible :) :)

[@harbselectronicslab3551]

Yep I can confirm that.....I am from Oz and he is definitely a Blue Heeler for sure......we love our cattle dogs down here......he is a lot like my old mate "Bluey" who I had to put down at the age of 16 years a few months back......it was the hardest thing I have ever had to do , but he was in a lot of pain, and I didn't want to see him suffer. I dont know how anyone can go through life without a dog.......they are just the best.

[@charlesmatthias9459]

@@harbselectronicslab3551 God Bless You Harb!Been thru that and it's the hardest thing a Dog/animal- lover will ever go thru!

[@TheMorphicResident]

This video saved me a trip to the tech. Couldn’t figure out where the hum was coming from but this video made me realize it’s 60 cycle and likely a tube issue. Seems like I tried everything until I swapped out the 12AT7 reverb driver and then silence.....thank you!

[@UncleDoug]

You're welcome, CB.......glad the video was helpful :)

[@jeffmclowry]

I'm deeply offended. lol You're so funny! I love your videos...

[@UncleDoug]

Greetings, Jeff, and thanks for the kind words. Glad to hear that you're enjoying the videos. I try to toss in a little humor once in a while to pep things up :)

[@Mr3DBob]

Lifesaver, Uncle Doug! I have a humming Princeton right now, so as soon as I get to watch this whole video, I'll know where to start on diagnosing my vintage FPR.

[@UncleDoug]

We're glad the video was helpful, Robert. Best of luck with your diagnosis.

[@djfrank59]

I've encountered the 60 cycle hum problem many times with 12AX7's especially with the Chinese tubes...There are times you have to swap out a few to find one that's quiet...I've also had situations where I would slightly re dress the heater wiring and the hum would vanish...

[@UncleDoug]

I'll try the re-dress first next time.....it's cheaper than switching tubes :)))

[@bullet0657]

Uncle Doug Hi Doug what do you guys mean by Re-dress.I am a noob when it comes to electronics but i would like to learn now that i have all these old guitar amps. Thank You.

[@djfrank59]

These as well as other amplifiers have both AC and DC wiring passing around throughout the amplifier...most amplifiers with the exception of a few others, have AC tube filament lines. AC hum can enter the signal by the wires passing close to DC or signal wiring and pre amp tubes which will induce hum; also due to the sensitivity and gain of the pre amp tubes...that's another reason why they contain metal shields...However, under the chassis, if AC heater wiring passes too close to the grid connections of the preamp tubes, AC hum can easily prevail...Dressing of the wiring is a matter of moving them at a slight distance as not to touch signal or DC wiring...This is another reason why if you notice that the filament wiring is twisted paired...If filament wiring is placed in a strait line, it can act as a dipole antenna and is subject to RF (radio signals) getting into the amp's signal path...I recently repaired a Fender amp for a customer who was picking up AM radio stations in his amp...

[@UncleDoug]

I guess that's better than picking up radio station transmissions with your fillings :) Thanks for the great info, Frank !!

[@rich1051414]

Yep, I have a preamp that has started to hum, and it uses chinese 12AU7's. The odd thing is, the hum value is not directly connected with the volume knob, but it gets louder around 75% volume then starts going down again after that. Very strange.

[@LuosRestil]

Thanks so much for this! I didn't even realize that the annoying 60 cycle hum from my Hot Rod Deville wasn't normal. A simple preamp tube swap has entirely eliminated it, and now I know what to have my ear out for when the capacitor gremlins come to call. Incredibly helpful.

[@UncleDoug]

LuosRestil You're quite welcome, LR. It's great to hear that the video was helpful. Best of luck :)

[@jambalaya7647]

A 60 Hz hum through its speaker even when the amp is on standby stumped me for a bit, Uncle Doug, until this video illustrated what the problem is not, and helped suggest what it likely is - electromagnetic coupling from the power transformer to the output transformer. Now to dope out the how of the what.. Your videos are both helpful and entertaining, Uncle Doug. Thank you for making them.

[@UncleDoug]

Try placing a fairly thick, grounded steel partition between the two transformers, if possible. It should reduce, if not eliminate, the problem. Even if it only reduces the hum, it will prove your theory. You're welcome for the videos :)

[@louisegilmour4366]

Ive recapped... retubed.... in an effort to try to remove a hum that existed on standby and the on position, slight hum with no volume control difference.... turns out to be a combination of a new speaker baffle with the speaker moved closer to the power transformer and a larger magnet.... electromagnetic coupling .... thanks !

[@kingdom-art7672]

brother, I want to THANK you for what you've done. I hope that my comment encourages you. I took apart my preamp and just slightly pushed it to the left! and boom! the humming/crackling was gone, eradicated!!!! I love you man!!! and your right! you did save me time and money! love you bro

[@kingdom-art7672]

pushed the tube*

[@UncleDoug]

+Thomas Johnson That's great news, Thomas. You can tighten up the socket a bit (use a tiny screwdriver and carefully bend each of the contact "circles" into smaller diameters) to eliminate a re-occurrence. It's good to hear that the videos are helpful :)

[@kingdom-art7672]

+Uncle Doug yes sir! bless you man I'll keep that in mind if I come into this problem again. thankd

[@UncleDoug]

You're welcome :)

[@Kiddomike]

I just got a new tube online and for some reason when I plugged it into my amp it produced a hum similar to a 60Hz hum. This is a very helpful video.

[@UncleDoug]

We're glad the video was helpful, KM :)

[@rondobondo6600]

Uncle Doug I just want to thank you for all of the time that you spent for us In making awesome and informative video's .I just wanted you to know that I appreciate all of your hard work....

[@UncleDoug]

That's great to hear, RB. Thanks !!

[@dwightjt]

You know Uncle Doug. You seem to be a kinda Rare breed of person When you come across a problem you make A video about it Educationally as if you didn't know all ready But I'm sure you are learning to as you Go along. I hope I'm Not puffing up your head. But your a humble man. Your teaching does not jump back and forth And create confusion. It's organized and Interesting. I think you Are helping a lot of People. And saving people money. I worked in quality Asurance before I retired 2 years ago Now I get to drink a beer And sleep in HaHa. During my inspections of auto parts one of the supervisors found out about my back ground Years of experiences In electonics electricle Wiring and mechanics Repair. And offered me a position to build Powe supplys to Test electrical parts like the head lights on the Chrysler 200 and 300 automobiles so Eventually I had to install solid state Relays and electronic Control module's For the 300 HID headlight projector Movements for testing. I built 32 power supplys for 100 to 300 Dollars a piece instead Of the contracted out 17,000 dollar a piece universal power supplys. I had chinese and Korean people wispering to me That I was saving to company hundreds of thousands of Dollars Of money I guess a good way to make friends I wish I was still there. It was a lot of Fun for me. So Uncle Doug I know quality When I see it and you are It. I had to repair them Often, the inspectors On the line twisted my Hand wiring around Untill they would break down so I made a few Spairs to replace one or two while I made Repairs on the units Used on the line then return it to keep the line going. Time saver Instead of stoping the line. It was fun soldering all those Hand made harnesses. Love your good work By. Dwight.

[@UncleDoug]

Thanks for sharing your life experiences, Dwight, and for your very nice comments :)

[@jamesjameson2369]

I would just like to say a huge thank you for this vid...after putting up with hum for a while I got a friend who knows a bit about it and said the problem was anything from capacitors to output tranny..after watching this vid I remembered I had a problem with a 12ax7 and had changed..Hum happened ever since so just changed and hum is gone..cheap fix on my Laney lc50..many thanks.

[@UncleDoug]

That's great news, James. Congratulations on a successful repair.

[@curtvincent3728]

Hey Uncle Doug! I really feel compelled to comment that I really, really appreciate you making these videos. You go over a concept slowly and you repeat that concept several times (it takes 7 times for a concept to penetrate our thick skulls) and your diagrams are very clear (old school, but that's fine, tubes are old school!). Give Rusty a treat, he is one hell of a guitar player too!

[@UncleDoug]

+Curt Vincent Thanks so much for your very nice comments, Curt. Rusty and I really appreciate them. P.S. He says thanks for the treat :)

[@49bednar]

Hi again Doug, Just built a 5F1 kit. Works great but has a hum, which I now know is a 60 cycle hum. I was prepared to live with it until I saw this video. It also has a fairly loud screech at full volume. Your video gave the idea and courage to poke around the 12AX7 socket. I found that pin 2 was a bit loose and as I fiddled with it, presto...no screech and almost silent. Miracles will never cease in the tube world. Thanks again for your great work. George

[@UncleDoug]

You're welcome, George. It's great to hear that the video was helpful. Best of luck with your projects :)

[@davidwindstrom2472]

Thank you SO MUCH. Believe it or not, this just happened to me with a 5751 (12AX7 replacement) NOS tube. I was going crazy testing ground loops, upstream components and cables, and was getting ready to send the amp in for repair. After watching your video, I pulled the single input 12AX7 (5751) I had recently rolled in, and problem solved. I couldn't believe it. What an obscure problem. Also interesting..the hum was only in the left channel (dual triode), and there was also a scratchy crackling in the volume control (fairly new amp). The hum did not increase with the volume though. Wild. I'm assuming the increasing volume increasing grid voltage masqueraded as a dirty volume control.

[@UncleDoug]

I'm glad the video was helpful, David. Congratulations on a successful repair.

[@IllusiveSwampMoose]

Thank you! I know this video is 10 years old but it was it was clear, to the point, and extremely helpful in troubleshooting my old reel to reel

[@UncleDoug]

That's nice to hear, SM. I'm glad :)

[@jamesromano3567]

I restore old electronics and this stopped me from trouble shooting the capacitors in my 1958 Harman Kardon Allego monaural amplifier. Had a 60 cycle hum that was constant and turned out to be the 6V4 fullwave rectifier. But then i still had a hum lower in volume. It varied with the volume control and it turned out to be the phonograph preamplifier 12AX7 tube. Thanks!

[@UncleDoug]

You're welcome, James. The frequency of the hum can really help determine the source. I'm glad the video was helpful.

[@aaronfidelisrecine]

Just fixed up a small amp with a 60 cycle hum. Filter caps had tested fine on the BLUE esr so I remembered your video and now im tube swapping. Thank you again for your videos! They are truly helpful and inspiring.

[@UncleDoug]

You're welcome, Aaron. I'm glad you're finding the Blue ESR meter to be helpful. Without it, you probably would have simply replaced all the filter caps......and still had a hum. I hope the tube switching helps. Good luck with your repairs.

[@stillcrazyafteralltheseyea1379]

I'm an electronics technician by trade, although I don't specialize in audio. Especially tube audio, which its it's own special mixture of voodoo and electrical witchcraft. I like to listen to things like this every once in a while to see if the author is dangerous, really knows his stuff, or is full of hot air.... I want to say your video was so full of hot air I had to leave the room...... but I can't. You were right on point with everything you said, as far as theory goes. But what was really cool is the way you explained it, both with the sig gen AND the little explanation on paper. Nice job. I'm actually going to watch more, because even salty old dogs like me can pick up little things we either forgot or didn't know in the first place. Keep it up, and thank you ! Peace, Matt Gee

[@UncleDoug]

Nick Gregg Greetings, Nick, and thanks so much. I was getting nervous as I read your comment, fearing that I was about to get my electrodes handed to me, but it definitely ended well. I'm flattered that an experienced tech would approve of my videos and look forward to future (hopefully positive ;) comments.

[@joeyshuster8569]

I appreciate your time put in to this video! This helped me diagnose the bad filter caps in my lowrey organ

[@UncleDoug]

Glad to hear it, Joey :)

[@sedici888]

I recently purchased an old Klemt M40 from ebay, and of course it had a Hum. I was going to try and fault find the device, and was going to concentrate on the caps. After watching this vid, the 50hz hum pointed me towards the valves. I replaced the valves, and the hum is pretty much gone. Thankyou so much for this, and all of your informative videos.

[@UncleDoug]

I'm glad the video was helpful and aimed you in the right direction, Sedici. You're welcome :)

[@brettgallagher6951]

Hi: Got my 30 watt amp build all straightened out. Hum was definitely not the power transformer. Had to fix the grounding layout and ground bus. Also found loose connections for the screen grid circuit and grid stopper resistors. Lots of loose connections. When I originally built the amp, think the soldering iron was not hot enough and I was using the wrong soldering iron tip. With a hotter iron and screwdriver tip, was able to get the connections very tight and strong. Amp works great now!! No more hum and buzz problems as I was previously having. The tone has also improved and the amp seems to have more output power now.

[@brettgallagher6951]

Thanks again for the great videos and helpful advice!!! Brett Gallagher / TubeGuy1975

[@UncleDoug]

@@brettgallagher6951 You're welcome, Brett. I think that figuring out all the mistakes we made during a build is probably the most educational part of the process.

[@jetblakink]

This channel is so good!… Wish I had it as a resource couple decades back!

[@UncleDoug]

Thanks, JB :) We do too.

[@122Music1]

We need more mentors like this in the world. Great post U.D... Thanx

[@UncleDoug]

You're welcome, 122 :) Thanks !!

[@31309586]

Thank you, I'm making a JCM800, it is the first amp I've ever made, and this is a very important information. Regards from Argentina.

[@UncleDoug]

You're welcome, GG. We're glad the information was helpful.

[@cdelonline]

I got a akai m8 tape reel to reel and took out the amps and to stand alone as preamps. I had 60 hum/ hiss forever and recapped the hole thing witch got a bit quieter and replaced el84 tubes. It has an other power tube in there I've been going bananas trying to figure out this hum. And your video saved me. I will replace remainder tubes tomorrow . Thanks and hope my hum goes away

[@UncleDoug]

I hope the tube replacement solves the problem, CD. Best of luck.

[@TroyLeonardO]

I CANT GET ENOUGH OF YOUR VIDEOS!!! FANTASTIC INFO!! THANK YOU!

[@UncleDoug]

You're welcome, Troy :)

[@joemicoletti]

You are a true blessing, Uncle Doug -- thank you!

[@UncleDoug]

Thanks so much, Joe :)

[@tim2468]

One of the fun things about this work is solving puzzles. You're a great puzzle solver!

[@UncleDoug]

+Tim Tim Thanks so much, Tim. One of the biggest rewards associated with technical challenges like this is the pleasure you get from solving the puzzle, and the pride you feel whenever you can turn an inert pile of smoking wire and components back into a functional device.

[@randyheath8566]

Makes a lot of sense to me Uncle Doug. I have a Koch Multitone amp head that is humming, so now I know what to check. Thank you very much for the Lesson. Love your Channel and you ❤

[@UncleDoug]

Check the frequency of the hum, Randy. Good luck.

[@bullet0657]

Hi and thanks for pointing this out.I have silvertone 1474 that has this 60 cycle hum and no amp tech around here could find the problem so i will re check my tubes one at a time. they checked the tubes on a tube tester and they all came out good to very strong.Thank you for post things like this Uncle Doug this will save people time and money.

[@UncleDoug]

You're welcome, Edwin. Thanks for watching and for posting an excellent comment. As you saw in the video, a tube tester can often give a false impression of tube quality. It simply doesn't check all the parameters.

[@1986yamahafazer69]

Man I wish I learned this decades ago. No time like the present! Thanks again for the lesson.

[@UncleDoug]

Happy to help, YF.

[@GoochGoocherson]

Excellent information as always! I am absolutely addicted to watching your videos since I found your channel. I have only recently gotten into tinkering with tube amps and converting tube radios. Largely influenced by a video you did converting a J.W. Davis PA amplifier into a guitar amp, being that I have the model 405 Davis amp, I was intrigued at the thought. Thank you again from the bottom of my heart for preserving this knowledge and passing it on for generations of people to use.

[@UncleDoug]

You're quite welcome, Josh. Good luck with all your projects.

[@keithhatton1975]

Uncle Doug, much appreciated, I was about to swap all caps. My hum, as you pointed out is a 60 cycle... valves I'm coming for ya.

[@UncleDoug]

I hope the video saves you some time and money, Keith.

[@kenq7948]

I'm getting exactly this sound on my fender bassman amp. Thanks a lot for the advice. Much appreciated.

[@UncleDoug]

You're welcome, Ken. Good luck with the repair :)

[@michaeldowning796]

Thanks Doug!!! Just got a Marshall head on the bench that has 60mhz hum and the customer said he just replaced all the tubes so just as you said I was thinking caps but inspecting them they look ok Now Im going to go through all 11 tubes on this thing (Marshall 6100LM, 7 - 12AX7's, 4 - 6L6's)....

[@UncleDoug]

Remember that tubes are only one possibility, Michael.

[@1thess523]

I believe this is what's happening to my blackstar 👍. Ordered a new set of preamp tubes yesterday.

[@UncleDoug]

You can test your theory by switching the existing pre-amp tubes around within the circuit......or simply substituting fresh tubes, one at a time. Good luck.

[@ess2586]

Huge help Uncle Doug....trying to decrease the hum in my 5E7 Bandmaster build and I did not know if it was 60 or 120 until you compared the two....it's definitely 60 cycle and now I know what to troubleshoot. thanks!

[@UncleDoug]

You're welcome. Thank you for using the video in the way it was intended, to help with elimination of hum based on its frequency.

[@moilimyacoub4580]

Woooow rhank you @uncledoug for this video. As I was just testing a BOGEN Tube preamplifier from 1963 and all Variac test passed but thenwhen I was testing the pre-amp.. I was hearing that kind buzz/hum continuous from the chasis of the amplifier. But when listening to music and raising the volume that buzz/hum sound didn't affect the volume and I was asking myself what could cause this. Now this clarify more about the myth or how to check these kind of situation. Thank you and keep up the great work sir ;-)

[@UncleDoug]

You're welcome, MY. Best of luck with your project.

[@Aijse]

Thanks for the examples of the hum at different frequencies!

[@UncleDoug]

You're welcome, Aice.

[@baron_orm]

I experienced this very issue with my 2008 Blackstar HT-5 Combo, heard the 50Hz (I'm in the UK) and wondered about input caps or tubes. Replaced the single power amp tube and it removed the hum completely :)

[@anthonyhitchings1051]

thanks for demonstrating the two hum frequencies

[@UncleDoug]

Thanks for realizing the whole purpose of the video, Anthony. Many, many viewers have simply read the title and then asked for long-distance repair suggestions to cure their hum issues.

[@heyartbailey]

Thanks for posting this! Just got done recapping and rebuilding a Bogen CHB-100, and was left with a pronounced 60 cycle hum. Rechecked all my work, outside foil orientation, etc. Saw this video, and put in a fresher 6EU7 and 6C4...bingo. There's still the slightest bit of hum there, gonna try to find a 12AX7 in my stash. This amp wasn't made with love and care, so it might just be something I have to live with, but I know I'm not going to even notice it when it's got Hammond organ screaming thru it.

[@UncleDoug]

You're welcome. I'm glad the video was helpful. One other thing to check is lead dress, Art. Use a wooden chopstick and move the pre-amp wires around.....see if any of them affect the hum.

[@bootlegapples]

Thanks UncleDoug .I'm doing my first conversion,a console tube amp to guitar amp,and after modifying it to accept a guitar I am getting a fair amount of hum when I turn the bass up..even with no guitar plugged in.I will do the 60 vs 120 cycle hum listening test.

[@UncleDoug]

+bootlegapples If the hum began after your modification, be sure that your input jack(s) are self-grounding, that your input circuit is properly wired and includes correct-value grid leak and grid stopper resistors (see my latest video series), and consider using properly-grounded shielded cable for all signal connections between jacks and the first tube grid. Good luck.

[@LongJim]

This is great info. I just checked out a Montgomery Wards Airline 6000 which exhibits a hum, but still produces sound. I shied away from buying it, fearing it had bad caps. It sounds like 60 cycle, so it may just be a bad tube. Thanks Uncle Doug!

[@UncleDoug]

You're welcome, Jim. There are many other causes of 60Hz hum, so keep that in mind.

[@mrGoesto11]

Little gems of information that have helped me along in my little hobby (obsession).

[@UncleDoug]

We're glad to hear it, Mr. G. :)

[@millstap]

Uncle Doug, I have a unique hum situation in my vintage 1959 5F6-A Tweed Bassman. All of the coupling caps and electrolytics have been changed out. It seemed to start after I did an electrolytic cap job over a year ago. Occasionally, I will be playing and then all of a sudden, the amp loses some power and the hum quickly builds up so loud that I have to jump up to turn off the amp. It sounds like the amp is getting ready to blow up. This build up of hum happens pretty quickly within 3-5 seconds. Then, I will turn the amp on again in standby. Once I flip the standby off, the hum is gone. I visually check the 5881's for possible redplating. Everything appears fine and I go on my merry business of playing again. This is an intermittent problem, maybe once every month or two. I just can't figure out why it would go away so quickly when I turn the amp off and on again. I think I will do another cap job and maybe use F&T's this time since I have never tried them. It's hard to tell if it's 60Hz or 120Hz. Any ideas? Could a tube do this and stop so quickly with an off/on switch cycle?

[@UncleDoug]

I wonder if you're not experiencing some sort of feedback oscillation, MS. Do your tubes all have grid blockers? If not, you might add them and see if the problem ceases. Also tap all your tubes to see if any are microphonic. While you're at it, tap all the capacitors and resistors in the circuit (with a chop stick) to see if you have any loose solder joints and/or microphonic components (it happens).

[@The_Absurdistt]

Absolutely stellar information. Thank you Doug. I just picked up a used SUHR PT100 SE for a decent price. When I turned it on there was what I believedto be a 60 cycle hum (will be confirming that very in the morning). There is also a large amount of hiss that increases as the output level is increased, especially on the higher gain channels. I suspect one or more 12AX7's.... Thanks again for sharing your wealth of knowledge!

[@UncleDoug]

You're welcome, O. Good luck with your repairs.

[@m.c.alejandrolizarragaliza637]

Nice video, you make that all tube stuff appear more easy to understan!

[@UncleDoug]

+M.C. Alejandro Lizárraga Lizárraga Thanks, Alex. That is our intention.

[@UncleDoug]

Landrew0, your comment had no reply capability, so I'll reply up here. Miller capacitance is amplification of the capacitance between the plate and grid, mostly in triode tubes, by the gain of that stage. It affects the frequency response of the tube but does not cause "hum". Here is a detailed explanation: www.aikenamps.com/index.php/what-is-miller-capacitance The capacitive coupling I describe in the video is between the 60Hz AC-powered heater filament and the cathode of the tube, which does introduce an audible 60Hz hum into the signal pathway. I hope this makes sense.

[@babybearkill1]

I'm starting to miss seeing Rusty.. Time for the next episode in Doug's amazing, fantasmagorical tube amp lectures. Very entertaining but semester break must be coming to an end I hope

[@UncleDoug]

Rusty and I have been wrapped up in some other projects, BB, including the building of off-road vehicles to race around in the desert that surrounds us. The second one is nearly complete, so we should once more be able to focus on amp circuits. Thanks so much for your continued interest and support.

[@19walter51]

thank Uncle Doug for taking the time these will help me a lot

[@larrydering1598]

Had to revisit this great info video. You have the best on the web. Thanks Doug.

[@UncleDoug]

Thanks so much, Larry. Welcome back :)

[@zachjarrett8730]

Thank you! Great troubleshooting step that can be employed early on to save a lot of headaches.

[@UncleDoug]

Thanks, Zach. It's not a cure for all hum issues, but it is a good first step :)

[@AmIonArock]

your video made since to me, and I think your excellent in teaching. your saying different tones mean different things. i am very new to working on my tube amp, which is a alamo dart. I went from no sound at all ... to a hum sound that gets louder when turn up the volume! It was very exciting . Now i have convert that hum sound to REAL: sound.

[@UncleDoug]

Greetings, AA, and thanks for the kind words. It sounds like you're making some progress. Best of luck !!!

[@joelewisband879]

I am so thankful for you and your video's You have helped me thru many nights of insomnia...😎👍👍☕🙏

[@UncleDoug]

We're here for you, Joe :)

[@robzecc]

I just fixed this problem thanks to your video! Thank you

[@UncleDoug]

Glad it helped, Rob :)

[@MrBluesina]

Nice tutorial, i learned something here. just a minor correction, two 100uF caps in series gives effectiveness of a 50uF cap with double the voltage capacity.

[@UncleDoug]

Thanks, Mr. B, and you are completely correct. I apologize for the oversight and will correct it.

[@brettmcnaueal1951]

Very well explained Doug. Always good to start with preamp tubes when it comes to hum. I’m not sure how many techs out there that would start with replacing capacitors to get rid of hum, and only come to find that even after they have replaced the filter caps, the hum is still noticeable. Microphonic preamp tubes can be a nuisance as well, as they usually check out okay, but can be very problematic when installed.

[@UncleDoug]

Thanks, Brett, for your nice comments and helpful input :)

[@SPWoz]

Thanks - I was going to replace filter caps - but now I will start with changing out tubes (I certainly have the 60Hz) ... I appreciate the advice. Great videos - I am just learning, and your videos really help.

[@UncleDoug]

That's good to hear, SP. Good luck.

[@qua7771]

Excellent. I just finished a fairly elaborate amp build, and got all paranoid about a 60Hz hum I'm getting. I'm also getting some undesirable distortion. I measured every component prior to installation, and double checked my solder joints to avoid this sort of thing. I'll swap tubes in the morning. Thanks.

[@UncleDoug]

Thanks, AR. Good luck with the repair.

[@qua7771]

@@UncleDoug Hey it worked! The whole time I thought I had a power supply problem, and would have to pull the board again. Your video saved me a bunch of time. The problem was the PI 12ax7 long black plate Raytheon that worked fine in another amp V1A. Odd! I replaced it with a new production long plate Mullard. The ghost note, (inter-modulation distortion) is gone. I'll have to donate. Thanks.

[@UncleDoug]

@@qua7771 That's great news, AR. Congratulations :)

[@alext2933]

Thanks. This has really helped me. Reassuring to know that it is probably a tube. Easily replaceable.

[@UncleDoug]

You're welcome. Good luck, Alex :)

[@joemcgraw5529]

45 trolls really? your at the wrong channel this guy knows what hes doing ,kids jeez ,sorry doug ,much respect to you really!!!

[@UncleDoug]

Thanks so much, Joe. Don't pay attention to the drooling idiots with the thumbs down.......no one else does :)

[@AndrewUnruh]

Love to hear ideas about this: About three months ago, I built a Fender Champ clone from a kit. I love almost everything about it except that it has a lot of hum and, because it only has one volume knob, there is no way to decouple the loudness from the distortion. IOW, you can't play loud and clean or dirty and soft. So, I decided to design my own amp, starting with the Champ circuit. Basically, I terminate the output transformer into a dummy load and then threw a volume control across that load and ran the tapped signal to a high powered amplifier. Now I had a "dirty volume" which was the original volume control on the Champ and a "clean volume" which was the tapped signal run to the high power amp. If I want loud and clean, I turn down the dirty volume and turn up the clean volume. If I want soft and dirty, I turn up the dirty volume and turn down the clean volume, etc. To knock down the noise, I am running the 12AX7 and 6V6 heater filaments using DC rather than AC. However, in the original Champ circuit, one side of the output transformer was grounded. In my infinite wisdom, I decided this was unnecessary and I left it floating - connecting the output transformer directly to the dummy load. The result was hum - not loud, but noticeable (it measured about 20 mV at the dummy load). So, I thought maybe Leo Fender *did* know what he was talking about, so I grounded one end of the output transformer as shown in his circuit. Dead quiet. So quiet, in fact, I thought I had killed the amp. So I plugged my guitar in and strummed a chord and it worked perfectly! So, why does connecting the secondary side of the output transformer to ground eliminate the hum? It is totally counter-intuitive to me. In fact, isolation transformers eliminate hum by isolating the secondary side from the ground. At least, that's how I thought they worked.

[@UncleDoug]

I assume you are speaking of the OPT secondary when you describe the effect of grounding one lead. Yes, it is essential to do this. In any transformer, there are extraneous voltages and currents developed in the secondary that are not related to the music signal being sent to the speaker. Grounding one lead allows them to exit from the secondary and not adversely affect the speaker/music signal......thus eliminating the hum they would otherwise produce.

[@rádiosantigos1958]

That explanation was a live saving one! Thanks, now I know that the hum is not coming from my new electrolytics that I have just installed on my old radio. Now, I will look elsewhere.

[@UncleDoug]

Glad it helped, RA. Best of luck finding the source.

[@UncleDoug]

Cy, your comment had no reply capability so I'll answer up here. There are different frequencies of hum (as the video explains) and all sorts of causes, including bad tubes, filter caps, lead dress, etc. The problem cannot be resolved by long distance, so your best bet is to either try to fix it yourself or take it someone who has the experience and knowledge to resolve the issue. Best of luck.

[@randorider2801]

Hey Uncle Doug! Thanks for the free education!

[@UncleDoug]

You're welcome, RR.

[@knuckle47]

Uncle Doug, thoroughly enjoy your videos. Thanks for the effort that goes into all of them. I know I am better for learning this.

[@UncleDoug]

+luthier47 You're welcome, L47. It's great to hear that the videos are helpful and appreciated :)

[@UltimateEnd0]

I have had the 60hz hum when I bought my "Bravo Audio V2 Class A 12AU7 Tube Multi-Hybrid Headphone Amplifier". I installed a gold lion tube before even trying the original tube. I also have it hooked up to a digital to analog converter from my computer.

[@UncleDoug]

Is there a question?

[@UltimateEnd0]

@@UncleDoug What is causing the 60hz hum? Is it the stock 1.5amp power supply charger causing it? Should I replace it with a 3amp one?

[@UncleDoug]

@@UltimateEnd0 I wish I could magically diagnose this issue long distance, but it's simply not possible. I'm afraid you'll have to either do on-site troubleshooting.....or get some qualified help. Good luck.

[@deluxetone]

Excellent as always. Thanks for all the great information.

[@UncleDoug]

You're welcome, DT.....glad you liked it :)

[@grilledcheeseeater3443]

Uncle doug your probably my new favorite content creator. great detail. and you get more veiws than you have subs regularly. which means your content is top notch

[@UncleDoug]

Thanks so much, GC :)

[@UncleDoug]

Mark, your comment had no reply capability so I'll answer up here. There are all sorts of causes of hum (including a bad tube) and, as the video explains, different hum frequencies. You need to take your amp to a tech who can examine it in person and diagnose the problem. Good luck.

[@ryanybos]

Thanks for the time saving information Uncle Doug !

[@UncleDoug]

You're very welcome, Ryan.

[@michaellfbvr]

You're the best uncle Doug

[@billmckenna7056]

Thanks again Doug, super helpful info, i had this issue some months back with a brown virbrosonic. took me weeks on head scratching before i randomly tried a new driver 12ax7. Never knew this about ac bleed between tube elements.. you are a great teacher😂👍🏻

[@UncleDoug]

You're welcome, Bill. Yes the internal capacitance between the AC filament and the cathode can cause havoc without being detectable as a short. About the only way to fix the problem is through tube substitution.

[@hydorah]

Working on a Laney AOR 30 at the moment has every kind of hum you can think of! It did have a couple of microphonic ECC83s. replaced all four it hums less now. It now has the higher pitched hum that increases with volume. Interesting with the reverb engaged it gets louder still. I'm replacing the big filter cap first then I'll see where I'm at. I've got a schematic so if humming persists in the reverb section I know where I'm poking! Your vids continue to be a great resource and I'm learning... little by little

[@UncleDoug]

Good luck with this frustrating problem, Hy.

[@hydorah]

@@UncleDoug Thanks for the good wishes. My Capacitor arrived. The old old one was marked 50uF (greek mu) a couple of times, with a printed colour code legend and a common ground which told me it contained to 50uF caps in one can - Very helpful. The new one was marked 50M + 50M (not nearly as helpful) but which I think, thanks to you (?) I was able to work out was another can containing two 50uF caps. Anyway got the thing install and bingo! Hum is now reduced to expected levels! Happy days! I'm now enjoying my first ever 6v6 amp. Cheers!

[@UncleDoug]

@@hydorah Congratulations on a very successful repair, Hy. Thanks for sharing your triumph with us :)

[@sigdaddy7377]

Hello again. I have gone back at it this evening and I now see that the actual tracing had peeled back. The reason the solder wasn't sticking at the contact point is that there was no copper contact there anymore. What I noticed as being loose must have been the tracing-- still soldered to the socket pin-- beginning to peel off the CB. I believe I made a mistake trying to repair that which wasn't even broken, at least not electronically/audibly. I've been compelled to make some wee jumpers to connect things on the two broken tracings. The other loose connections had no tracings. It sounds much better now, but I anxiously await my new caps to replace the leaky ones-- then I'll know more. Is this bizarre, the tracings peeling away, or something you've encountered before?

[@UncleDoug]

+sigdaddy I don't generally work on PCB amps, Sig, so this is not a occurrence that I am familiar with....however, I can see how it would happen. You have taken what I believe to be the only correct move to rectify the situation. Again, you might want to stabilize any loose connections with epoxy or silicon. Hopefully, with the new capacitors the amp will be good as new.

[@jk-76]

A life saver all these years later...

[@UncleDoug]

Better late than never, J & K :)

[@Raiders757]

I didn't want to offend anyone, so I subscribed. Great info by-the-way. despite having played guitar since 1980, I am new to tube amps. I bought a used Haze 40 and replaced the tubes a few months ago. Sadly the first set of tubes I got kept blowing the fuse out. The replacement set works great, but when I made my first attempt at biasing them, I think I had my ground hooked up wrong. It may have been touching something, becasue I couldn't get them to even out. Anyhow, I ended up with a lot of crackling sounds, and a low pitched hum. I discovered the error of my ways when I opened the amp back up and now have the tubes biased to 38. Sadly I still have the constant hum, Btu the crackling sound is gone for rhe most part. I checked everything, guitar, pedalboard, and despite having an original Rockman Smart Gate (bought new as a young a lad), the hum is still present. I was thinking it might be something within the amp, but now I am wondering if it's my tubes. The amp sounds great, but the hum kind of worries me. I am still hoping that it might be some sort of outside interference. My practice area is around a lot of devices. Stereo, PC, and the room is right off the kitchen with microwaves, coffee pots, etc...

[@UncleDoug]

Rusty is very pleased to hear that you subscribed :) Re the amp, I assume that the 38 refers to the mA of plate current, but this is not an accurate way to bias an amp. Please watch my video on how to bias a DE amp by adjusting the plate dissipation. As far as the hum, it sounds like you may need to get it looked at by an experienced tech. Best of luck.

[@denismpoiriersr3339]

I liked the video so much I couldn't help adding my 2 cents to help others with this issue. What would be fun is to apply DC filament voltage on just that tube in that location to put the final proof of the cathode/filament capacitance coupling theory.

[@UncleDoug]

+Denis Poirier Thanks again, Denis. I rely upon knowledgeable viewers, like you, to contribute to and improve the overall video content. I still have the tube, so further testing and confirmation of capacitance could be done. If the outcome is interesting, I'll add it to the video description.

[@copytekk]

This was super helpful. Thanks Uncle Doug!

[@UncleDoug]

Glad to hear it, Aaron :)

[@TheTuckmorgan]

Thank you for posting. I've been wondering if the tubes in my 67 reverb needed to be replaced. They're still rockin. Again, thanks for the post

[@UncleDoug]

If they still work, keep using them, Tucker. People change tubes way too often and for no good reason.....at least in my humble opinion.