Finding A Bad Tube In A Tube Amplifier 

Yep. It’s not a halogen lightbulb, it’s a vacuum tube.

Another funny thing was he tried to listen for microphonics on the rectifier tube!

Why take the chance? I just tested my headlights with a drumstick.

@@Danielburke-go8dc I was a Type C color darkroom technician all my life. (until film went to digital) The bulb in the enlarger was halogen. We never touched the bulb. The reason was, that the oil of your hands would change the color (Kelvin Temperature) of that bulb. That was why. It never shortened the life of a halogen bulb to touch one. That myth all started with not touching darkroom halogen bulbs and spread to everything.

Been a BMW technician for 8 years and touching the globe is an absolute no no. The amount of globes I've had to re-replace because the apprentice got his fingers on them.. not saying its applicable to vacuum tubes but when it comes to cars.. its not about the colour its about residues remaining on the glass can't dissipate heat as well as it should when 100% clean and it causes internal temps to raise beyond spec. You can literally see the finger prints burnt into the and the filament damaged on the other side of the glass directly at the point of contamination.. I suppose automotive applications have a much longer on time/ heat aswell so maby not relevant to vac tube amps.

Thanks!

Glad it helped!

You're welcome!

+Casey Jones Thanks for the tips! Yea I ended up replacing all the tubes down the road because it was about due to replace (I play pretty hard, and have the power tubes biased pretty hot). Unfortunately this Tweed twin is going into repair because a transistor got burned out and the whole amp shut off. Been using my Blues jr. for now. Love that amp too! Thanks again for the tips, cheers!

Damn! I thought to myself "wow! Never knew that!" 😆😆

Hhhhha

There's some truth to it actually.

No, for real. The second I heard that, I said out loud "You cannot possibly be serious".

@@RyanMcQuen no there’s not.

+fullcirclejams. Thanks man! Yea I love this amp!

Thanks for that! I don’t know why some/most treat it like a halogen bulb! 🤷🏼‍♂️

Yeah. It's the first few stages of the amp. I'd expect them to be slightly microphonic at that volume. Especially the tube that has the very first stage in it.

Thats right, I have only needed to change valves once in 17 years on a combo used every day.I think they are using low quality bases and not checking the circuit cis you can get that problem in a brand new amp.

They are very expensive man cave items now.

Thanks man! Yea I love this amp, it's my number 1 for sure! It was a reissue the custom shop had in the early 2000's. This one is a 2006 model. I think the custom shop is bringing them back, but they don't have the Ted Weber speakers in them. It sounds amazing!

+Ariel Gomez Yes they did :). Not sure what the squealing sound could be from.

The regular ground cable. It's actually very short according to me and my amp tech. Cheers!

No, that is perfectly normal. It is called "micro-phonics" it is due to the metal parts inside the tube vibrating which causes a resonance, doesn't necessarily mean they are bad. Usually when a tube goes "bad" the filament burns out or the cathode depletes.

Tobias Rechsteiner Dont do it. If you touch a charged capacitor you can actually die. Even if the amp is turned off

+Mentas. I would maybe first try to plug the amp in another outlet to see if maybe that cleans up the humming. Also, if you put in new power tubes without a proper bias job, that may be your first culprit. Hope this helps! Cheers!

Thanks for the tips. I don't have any other guitar cords and at some points the hum stops in a certain position the way I hold the guitar. I think it might actually be a faulty cord. I've had it for a really long time and it hums on my other amp as well. I think I found the problem.

+Atul Sharma. Hey there! Yea don't worry about the amp to get any kind of overdrive for now. Sure there's tubes that have more gain in the preamp section, such a 12Ax7, while a 12Ay7 is more of a traditional 50's-60's sound. However, your amp needs to be able to take those tubes, some amps don't like to switch to different kinds of preamp tubes, (bottom line, don't worry about the preamp tubes). I would get an overdrive pedal. My favorite kinds are based off a klon and the ones based off tube screamers. I use a Mad Professor Sweet honey Overdrive and a Mad Professor Little Green Wonder. They make 2 versions, a hand-wired kind and a factory pressed circuit board version (non hand-wired). Depending on your price range you can get the same tone. I recommend hand wired as much as possible just because I've had the Sweet honey hand wired for 6 years and it hasn't given me any problems. The little green wonder hopefully lives up to it's brother! Hope that helps! Cheers!

Hi Renato, Thanks for the response, i appreciate it :) ill consider buying there pedals, but there are different kinds of ecc83 valves, do these different kinds of valves give me different gains ?, i know that 12AX7 is 100 for the gain

I haven't heard of any ecc83 valves. I do know of el84's and el34's, but those are power valves (or tubes). Those can never be changed, so make sure you stick to the type that's in your amp already when you want to switch those ones out (usually 2 or 4). I highly recommend you just look at pedals to get the sound you want, I wouldn't worry about doing things with the amp right now. Hope this helps! Cheers!

ECC83 is the European designation for the 12AX7.

probably preamp tube or wiring from jack

To my understanding, Marshall do not make tubes, they buy in their tubes from other manufacturers who put the 'Marshall' logo on the tubes. Sometimes the original manufacturer's logo may be left on, other times not. Have a look on your tubes for evidence of another manufacturer's logo . . . like Sovtek for example. I've never used them (haven't had to replace any tubes yet!), but I've been told that JJ tubes represent good value for money, and produce excellent results in Marshall amps. Don't just take my word for it, speak to other musicians preferably those who use Marshall valve amps as part of their kit. sorry I can't be of more help.

Daniel Auen Yes. The capacitors usually discharge in a couple months

xd

+Jonathan L Hi Jonathan, yea this video doesn't do the best justice in picking up the audio in the room. However, tapping the preamp tubes and seeing if they cause echo, feedback, or a reverb-like effect will be a sure find that that tube is microphonic. The preamp tubes that usually go bad by the way are the first preamp tubes in your amp. The first and second preamp tubes in this video was for sure microphonic. I wouldn't say you need a trained ear to tell when tubes are starting to go bad, however, power tubes also have their signs as well. Some of those signs are, loss of volume, and muddiness or dullness in tone. Hope this helps. Cheers!

Renato Pasqualini, i think you just helped me a lot, dude! My fender blues junior have lost the bass and i was thinking if i'm imagining it or there's something wrong with the tubes..And guess what? One of the tubes have that reverbish sound on the full volume.. I would describe that sound like drops of water are falling in to a big metal bowl. Gonna try to replace it, thank you!

+Erick Hernandez Thanks Erick! Yea tubes can go bad at unpredictable times. I just recently had to put in new tubes a month ago. Based on the way you play and how you bias your tubes (hot), they can burn out surprisingly fast. I would say the crackling is a sign that the tubes are already going bad. Hope that helps. Cheers!

Yes.

Yes it can, and to find out if it's a tube or not, cut the volume on your guitar, hit the amp chassis if it rings and feeds back, you've got a microphonic tube (or a bad capacitor but most likely not). What this video is demonstrating *is not* a microphonic tube, it's a loud tube but definitely not microphonic. If he had have swapped the 2 over for the other 2 he would have been fine.

A amp tech told me to unplug the amp while strumming a plugged in guitar, to drain the filter caps. I don't know how safe it is, but I can see how that could make sense

@@justinpaquette224 shouldn't a tube amp been put to standby mode for a while before taking power off?

@@mekakorpse It might be a good idea, but I think its more important when you are turning the amp on

Touch all you want. Old equipment always has grungy dusty dirty tubes installed. This isnt a halogen light bulb, it will be fine. Clean tubes look nice and dont smell funky when they light. Your fingers wont hurt your tubes.

Caleb Welte What is causing the horrible popping when touching the amplifier on top?

I'm sorry I don't know. It could be a number of things. Buy deoxit and put a small amount into the input jack and plug in and pull out the plug a few times with the amp off of coarse. If that don't fix it IDK where to start from this end. I doubt it will fix it, but it might.

Hi Michael. Yea your tubes won't fail if you touch them a few times, however, if you are working on them and touching them constantly, any oil that is left on the tubes will cause them to fail prematurely. Couple of things I would advise: 1. I would not "touch them all you want" YES they WILL burn you. This is gas being heated in a glass tube, it's not advised to touch them while the amp is on or if you just turned the amp off. Wait a few minutes for them to cool down before doing that. 2. Please DO NOT pour anything into the input jack! The popping sound is either one of these 2 things. The tubes (most of the time they go bad, they don't last forever. Or there's dust in the input jacks, or in the tube sockets. You can actually carefully take the tube out, and use a air duster and blow any dust out. (This has been the case for me many times)

Simply not true. You are thinking of halogen light bulbs. There is no evidence anywhere that oils on your finger will hurt your tubes at all. simply made up.

Bad

Thank you!

I'll give you a thumbs up after I put my gloves on

Dannie Moore That's the 1st thing that I thought !!!! Kudos to both of you !

Why though?

No. Or yes. The filaments that make the glow, are a totally different circuit to the rest of the tube. The amp won't work if the filaments aren't working, but that doesn't mean it's a bad tube. If none of the tubes glow, it's probably the filament power supply - those thick twisted wires that run to every tube. If you're getting around 6.3 volts across those, then it's the tube. If the heater in one tube fails, it won't affect the others. They should still work. Bear in mind that some tubes have the heater filament tucked away where you can't necessarily see a glow. If none of the tubes are glowing, check the filament wires to make sure you have continuity all the way along. At some point along those wires, there will be 2 big resistors, both connected to the filament wires on one side, and to ground on the other. Replace those. They often burn up. The amp usually still works if they do, but is very noisy. If you get no voltage at all across the filament, but there's no obvious break in continuity, then you got the absolute worst case scenario: The actual filament winding on the mains transformer is dead, and you need a new mains transformer. (Unless your filaments are powered by a separate transformer, in which case you just need to replace that) But no, a tube does not have to visibly glow, to be a good tube

Just got a budda SD18 and the v1 tube is visibly bright. The other two have me wondering. Not sure if they work, but the amp runs quietly 🤔

@@ashscott6068 thank you for your knowledgeable reply 👌

What you tiuching it with your fingers when its hot do you stick your hand in the toaster no wait let it cool .or grab that hoty and hold on.

Everthing is apreciated .

What does a rectifier tube do? I just got my new amp and it has one but I've never had an amp with one before.

+John Simms It should be ok, if you don't bang the tubes too hard. I ended up just replacing all the tubes btw. Cheers!

@@SteveRyan1965 you shouldn't hear anything come out of your speaker when you tap the tubes. When he tapped the bad tubes the noise came through the speaker.

Probably because I needed to disconnect it to get the back panel off.

+Chaos Entertainment Well that quote is just not accurate, isn't it? If you tap a microphonic tube, it will give a responsive to that tapping. Microphonic tubes tend to be the preamp tubes, so when you tap one and it gives you a response, I believe that's a most likely way of finding the culprit. I wouldn't say what I did is a "rediculous" diagnosis test, it's actually a really good way of finding a bad tube without fetching a lot of money on a tube testing device. You're going to eventually replace all the tubes, so spending money on a diagnosis on your preamp tubes really seems ridiculous to me to be frank. It's not more complicated than that and when you find a microphonic tube, it doesn't mean all the tubes in the amp are bad. "I tapped my tubes like it said on the internet, and ALL my tubes are microphonic" That's just not correct. I hope you tell your customers that. Cheers!

Do your research. You may get away with it many times, but all of the real life experience that has shown it can drive a tube into a microphonic state aren't inaccurate.

What's the point? If you're getting high pitch noise, or unusual feedback, and you find a microphonic preamp tube, that's most likely the culprit. So it's time to swap that tube out. I'm sorry, but I can't believe every customer's tubes have become microphonic by tapping them. That's probable, but unlikely. Cheers!

"If you tap a microphonic tube, it will give a responsive to that tapping. Microphonic tubes tend to be the preamp tubes, so when you tap one and it gives you a response, I believe that's a most likely way of finding the culprit." This is just not correct... A ringing tube is microphonic, if it amplifies your the thud of the tapping it isn't, all tubes are somewhat microphonic when you tap them by design, especially the louder the amp is and microphony will vary depending on amp as well A tube recreating the sound of you hitting it *is not* microphony... and it's true some tubes will be dead silent some will not be, because they aren't all made equal, that doesn't mean that the loud tube is microphonic, actually that is one way you test for what tube you want to put in V1, the less microphonic of all is what you want at your input, same goes for the PI, you'd want a quite tube in that position as well. Microphony is when you get feedback from the tube. But yeah hitting them repeatedly will make them microphonic at one point thats for sure.

+Christopher OTrust me, tapping a preamp tube isn't going to damage this amp. You don't have t spend that much money for something to test a preamp tube, but yea they do come in handy.

and whats the better way? tell us

Four year's have past, and he hasn't told us the right way of testing

@@DrVulatar That's cause he has none.