Replacing Tubes and Biasing a Marshall JCM 900

[@Joska43]

Thank you very much ser! Simple, direct without any bullshit as on others videos.

[@paulfabrique5055]

I am lucky enough to have an early JCM900 with EL34s. They came with brown base Teslas. These amps get maligned, by the same people who revere boutique solid state overdrives (fuzz boxes)...for me the high gain sound of these amps if far more musical than any pedal Ive heard. And I have tried a lot.

[@TheRosswise]

Good video, and thanks for not putting in any music. I get so tired of the stupid music people put in videos like this.

[@davidbomar50]

Worked great. Tubes cost a little more than I would have liked. But very happy with the sound!!! Thanks man.

[@paulfabrique5055]

There are also two test points on the PCB were you can measure voltage across for bias. They are on the schematic.

[@blakjack3053]

The JCM900 uses clipping diodes and I'm good with that!

[@JoeTurmes]

@hsvdt I have heard this with things like car headlights, but from what I have found isn't the case on power tubes. Not sure why. If you got some info, I would be glad to look at it, though.

[@janinapalmer8368]

You should test both opposite pairs of output tubes !!

[@helikyler]

I'm not an electrician or an amp tech which is why I'm seeking guidance on KZbin... but wouldn't it be worthwhile to warn people 1) to discharge the amp with the power and standby switches on and the amp unplugged, 2) not to touch the tubes with your fingers (which you seemed to be doing without much worry, so maybe it doesn't matter) and 3) what you can and can't touch so you don't get your butt zapped? I've just read a lot of sites that say very seriously that you could get killed.

[@Satan6666ful]

You should also mention to use cloth gloves as to not get hand oils on new tubes. And always set up and bias tubes and amp every time even with the sets of power tubes and preamp Its really nice to see the how to do . It would be nice if you showed how t change sound o amp as well El-34s are nice I like 6550 s and 12x7s I have over twelve Marshall 800 & 900 amps and set them up with new tubes every time I get one and set them up the way I like them to sound . Great tutorial . Thanx

[@MikeAndersonvinyloldies]

The hand oils thing is a myth. I've seen lots of amp techs not use gloves. It's wise to wipe them down real quick at the end but you don't need gloves.

[@jkdelawrence]

How do I know which pre amp tube is the balances one?

[@JoeTurmes]

@fukskating That is a Multimeter. It is sometimes called a DMM (Digital MultiMeter). It is used for measuring voltage, current or resistance in a circuit. Using the bias probe I got from Eurotubes, it allows me to measure the current going through the tube in order to properly bias it.

[@JoeTurmes]

@fabiolone70 Measure plate voltage with a DMM on the backside using the voltage setting. Either use a different DMM or unplug the one you have connected to the bias probe.

[@tontonsixtysix]

thank you man good vidéo for thic mitic beast

[@jawsrock1]

Hi Joe, this was a great video, but I noticed something: You stated that you must put the red lead of your probe on the mA input on your multimeter and set the multimeter to mA, then the next thing you stated was to check the plate voltage. This could be bad if someone actually did this...especially with a cheap multimeter.

[@SaintFredrocks]

Many multi-meters have a 10A and V/Ohm/mA input and one for the ground. To measure plate voltage you use the second one. The 10A scale side is just for higher current measurments.

[@IndyRockStar]

wouldn't you want to find out the plate voltage and load the tubes in on the bias tool first before installing the tubes?

[@blackknightrocks]

I have the JCM 2000 DSL 100 Marshall Head. Has sound problem. Tried to bias and cannot get any voltage reading on right pin. Replaced tubes and same thing. Switched out all tubes including pre-amp tubes thinking one tube may be bad, same thing. Any thoughts?

[@MrDrognRoll]

You Might explain how to measure the plate current? To adjust the bias, it must be power on button and the standby button in on?

[@silasfatchett5693]

He is using the bias probe to measure the cathode current which is the plate current plus the current drawn by the screen grids, which for an EL34 is unlikely to be negligible, resulting in the tubes being biased a little colder than he intended. Measuring actual plate current means delving into a live amp, not a good idea for a newbie. Yes, the amp must be switched on and not in standby mode, and incidentally should have a speaker cab or a dummy load connected.

[@mcristianoferreira]

Good video, my JCM 900 is with 3 válvulas12ax7 burned , but continues to speak out , that may have damaged some other component ? thank you

[@taglish123]

Hello. Would you have the same tutorial for jcm800...2205 by any chance? Or could direct to the right direction?

[@JoeTurmes]

@helikyler 1) Not sure what kind of capacitive charge is being held in the amp....I have seen anyone even be concerned with this, so it would seem like a non-issue. 2) I thought about this too, but talking to some old pros, this doesn't have the same issue as say the headlights in your car. I suspect either the glass is too thick to matter or the tubes dont get hot enough to for the oils on your hands to affect them. 3) As long as you are handling only the chassis, you should be safe.

[@whitherance]

What a Great video!! simply the best one to show every steps. I'm going to try on my amp which has 4 6V6 tubes, is it the same like yours that I have to test on one 6V6 for the bias value? and should I have the same multimeter to measure the plate voltage? thanks

[@TimestampMusic]

1. On certain stores, one can find packages of four matched tubes, usually called Quartets, specifically designed for push-pull systems. Do those need biasing too please? 2. What was that thing you said on 4:12 about the "balanced pre-amp tube" going to V3? Aren't all three ECC-83's that have to be used, the same? I've always used three identical ones on every change and had no problems (so far). I must mention that I am using a JCM 800 2203 model and not a JCM 900 but as I see, they look identical.

[@JoeTurmes]

I'd bias them as well, unless you know you have always had matched tubes. Even then, I'd still bias.

[@TimestampMusic]

Joe Turmes Ok, thanks. About that third ECC83? Does it have to be different than the other two?

[@JoeTurmes]

Timestamp Webmaster I bought the kit from Eurotubes which indicates a specific high gain balanced tube for V3. Not really sure if it matters much, I just followed their recommendation. Heres the retube kit page: www.eurotubes.com/cart/index.php?page=view_products&category_id=9&sub_category_id=136

[@TimestampMusic]

Joe Turmes I checked the retube kits they've got for JCM 800's and it seems there is one different ECC83 on those ones too. Turns out your video is very very useful and teaching. Thanks a lot. ;)

[@silasfatchett7380]

If they are matched it means that they are the same as each other, but not necessarily the same as the tubes you are replacing, so biasing is highly recommended. A 'standard' ECC83 (or 12AX7) will be fine for the 'balanced preamp tube' which is actually the phase inverter tube. All tube guitar amps have slightly unbalanced output stages which encourage second order harmonics which 'sweeten' the sound of the amp.

[@bobbarcus8310]

here do you have the dials on the DMM set at? Is it in the 10Amp mA on the left of the common ground,and where is the setting you turned it to? No one will show or tell me how and where to set the DMM.... Thanks

[@JoeTurmes]

I wouldn't. Electronics Contact Cleaner is pretty readily available at your local Radio Shack or equivalent shop.

[@kevinwalker4124]

I'm assuming you drained the power out of the capacitors? I'm learning be patient with me.

[@JoeTurmes]

@fukskating It is recommended to bias the amp any time you replace tubes. This goes for all tube amps, as far as I know. If you need help biasing your amps, contact the pros at Eurotubes. They are very helpful and know what they are talking about. They also have guides for lots of different amps.

[@Mikem-mq2hh]

you only bias one tube? i guess if you know they are from the same lot correct?

[@Just4you2010]

The multimeter will only display the current value after 15 min?

[@JoeTurmes]

I do not follow your question.

[@Just4you2010]

@@JoeTurmes the multimeter is only able to read the measurement after amp's warm up for 15 minutes? Never mind but thanks for your replied. I just found out my tubes bias tester testing on pin #8. It suppose to test current on pin #3 instead. :)..

[@scruffy2365]

Thx. Ive ordered my valves and bias tool from eurotubes. Did you notice any better performance after the revalve?

[@TheDannyGoodman]

How do I put 6l6 tubes in my Marshall JCM 900 Hi Gain Dual Reverb, when there were EL 34s inside before? Thanks.

[@JoeTurmes]

Any reason why you want to do this? You will have to rewire the sockets to do it.

[@TheDannyGoodman]

@@JoeTurmes The 6l6 tubes were recommend to me for a more aggressive sound from the guy at the shop - all I told him was that I have a Marshall JCM 900 Hi Gain Dual Reverb 100W. Unfortunately I did not know that there were EL34s inside my amp before. Last time they were exchanged was five years ago and I had absolutely no idea about amp heads/tubes and it was done by an amp technician for quite a price.

[@WillyBooger]

Thanks for the video. I have a Marshall DSL 40c, and I cannot find anywhere anybody shows how to bias it or even find schematics on that model. Unless it is so similar to the 401's that it is assumed to be treated the same. I have a DMM and just want to check the bias and know what Marshall recommends on the setting. Would you know about this? Thanks again friend :-)

[@THEsyntheticFresh]

nice video. I´m looking for replace valves of my JCM2000, you know if is the same way and method?

[@fspeed180]

i have just received a JCM800 however it has 6L6 tubes in it?? Its a 50W mast model Mk2 and I am certain they are EL34? Any ideas? How do I know if this is just a mistake and it should have EL34's and that its not been modded?

[@JoeTurmes]

You can put 6L6 tubes in there I think.... Buy it used?

[@fspeed180]

yes I'm gonna get the bias checked over

[@MBString]

Hi, great video! I have some questions.. do i need two multimeters to bias the amp? And how do you know which one is the balanced preamp tube, i thought they are all the same and that you can just swap them around as you like? how come you have KT77 tubes in it, i have 6L6 in mine, is the wattage of these tubes the same? Sorry i am a complete noob in this, but i would like to change tubes myself, because amp techs charge much too much for this in my country

[@silasfatchett5693]

The three small tubes are all ECC83 or 12AX7 and can go in any order. First determine the maximum plate dissipation for your output tubes (6L6 - 24W, 6L6-GC - 30W). Use your multimeter to measure the plate voltage (pin 3) then you can do the calculation to find the current required for 70% dissipation. Then you can use your multimeter to set the current. Joe is using a bias probe which allows current to be measured directly, but some bias probes determine current by measuring the voltage drop across a resistor. Read the instructions that came with your bias probe before making the measurement.

[@MrDrognRoll]

Hi, I have a Head Marshall JCM900 Dual Reverb 4100 that use tubes 6L6, i want to ask you if the bias adjustment is performed of the same way that you explained in the video? Is done with the distortion button activated or with the clean channel? Just teste installing only in the last tube sockete? And the last one is if you can explain me how to obtain the plate voltage? Sorry for my english but i´m from Chile, thanks you very much, I hope you can healp me becouse were I live nobody do this job

[@themathrock1607]

great video. Thanks!

[@jayhallman6666]

My JCM only has 2 big tubes. Does 4 tubes mean it’s a 100 watt amp?

[@louderthanlightphoto]

Yep, 2 tubes = 50w, 4 tubes = 100w

[@SouthernPrinceKenny]

Are the same voltage/current values the same for all brand tubes for replacement in the 900 4100 100w amps? I want to put Groove Tubes in mine. What models # tubes are needed for the preamp and pwr tubes? I'm experiencing squeeling when I use ac pwr pedals... guitar only plugged in and also batt pedals no squeellng.... What's up with my amp? Thank

[@camax8247]

Nice video.if i don't connect the load to the head and i turn on the Power and standby without input what happen?

[@JoeTurmes]

You risk blowing your output transformer.

[@camax8247]

@@JoeTurmes thanks joe...you know if is it possible to put varicac to supply the final valves(5881) with less voltage for changing headroom and dreaming have a better sound without high gain-volume (similar like van halen)?

[@camax8247]

or put variac between output of jcm900 to cabinet 1960a is it dangerous? i'd like to have sound like when i left maximum value of gain and volume is amazing and reach of armonic frequency, but of course i can't do it cause neighbor..how can i have that sount with low volume?

[@JoeTurmes]

@@camax8247 Some people put a Variac on the wall plug to change the sound, thats what EVH did. A variac on the output tubes is likely going to be a difficult mod, and not get the result you want.

[@JoeTurmes]

@@camax8247 Between the head and cab, what you want is an attenuator or load box. I just picked up a Torpedo Captor X for my son and his 5150iii, that should give you a ton of options akin to what you are trying to do.

[@fabiolone70]

nice, just a couple of questions : do you measure the plate voltage throught bias probe and tester just switching it to Volts scale or whatelse? (f.e. touching with red tester pin the n°3 and chassis with the black one?) thank you.

[@silasfatchett7380]

With the black lead clipped to the bare metal of the chassis, set your meter to its highest DC voltage range and with one hand, with the other hand behind your back, measure the voltage on pin 3 of the tube.

[@joshmartins560]

I've always just swapped out EL-34's and never had an issue ..I read that the pre amp tubes don't need to be biased?

[@JoeTurmes]

I don't think preamp tubes are typically in a push-pull configuration and that is why they don't need bias. As for not biasing your EL-34s, you might just not be operating optimally, or you have been lucky to get close enough to matched sets for it to not matter.

[@JonasBygdemo]

Josh Martins I'm no expert at this. But preamp tubes are generally cathode-biased, often referred to as "self biasing". Power tubes can also be cathode biased, but those are generally lower wattage amps. More powerful amps are generally grid biased, and on those amps you definately need to bias the tubes when you change them. But why not just check the bias on the preamp tubes as well? The amp is out of the headshell/cab, and you've got your multimeter out.

[@DreidMusicalX]

Will Deoxit D5 work ok for this?

[@JoeTurmes]

Should work fine.

[@ljmetal666]

So you only have to bias on tube to get it right or is all of the power tubes?

[@JoeTurmes]

@blinkairwavesracer44 From what I understand, KT88s won't fit. Some claimed to have been using two KT88's instead of four, and using the 16 ohm setting. I don't know much about this technique and wouldn't recommend it without researching it first.

[@electrickithara]

What's the best contact cleaner to use for cleaning the tube pins and sockets?

[@JoeTurmes]

I just use the Electronics Cleaner from Radio Shack.

[@electrickithara]

Thank you.

[@JoeTurmes]

electrickithara No problem!

[@guacadu]

what happens if you replace the tubes but don't adjust the bias??

[@JoeTurmes]

Potentially you wont have a balanced circuit which will cause sound output to suffer or shortened tube life.

[@guacadu]

thanks joe I think Ill do the whole job

[@clintgilbert9358]

I got ? I have Rivera k100 I was playing last night channel 1 sounded out of phase los of volume and slightly feeding back channel 2 tube sounded good and when played threw the fx loop sounded good. went home for lunch and channel 1 sounded good. im baffled any one with suggestion what could be going on?

[@MachineKnot14]

Would you need to bias if you use the exact same tubes, just brand new ones?

[@wildwoodtop]

yes, new ones could differ just a tad (bias is common practice just to make sure it's perfect)

[@Toys_in_the_Attic]

One question:If you accidentally touch those big open-blue caps(?) next to the power tubes is there a danger getting fatally electrocuted?Forgive my ignorance,I've almost no idea about anything electrical...

[@peshmadscientist1833]

then stay the hell out of there!

[@robbieflower1119]

As long as you stay away from the metal terminals on them because capacitors can hold charge

[@defin99]

I just plugged my (2) el84's straight into their places and my amp works fine.i did no biasing at all.

[@serdiezv]

Fixed bias probably, but most amps with El84s do fine as long as they're matched

[@defin99]

the writing on the box said they were matched.

[@jawsrock1]

They may work, but you may not be getting maximum efficiency (headroom, power, etc.). You could also have just got extremely lucky and the bias was the same.

[@xpicklepie]

thank you for the absence of mindless babbling.

[@keza123123123]

what is max watt dissipation?

[@silasfatchett7380]

Max dissipation is the maximum amount of power that a tube can handle before it overheats and damages itself. When a tube is working, its plate gets hot, and must 'dissipate' or radiate away the heat. Dissipation is measured in Watts, and is specified on the tube's data sheet. E.g. max. plate dissipation of a 6L6GC is 30W.

[@msaintpc]

The lettered instructions went by so quickly that I couldn't quite read them.

[@TheZtovski]

nice tutorial thx

[@JoeTurmes]

@CosmicSPC Not true. You bias based on throughput current.

[@BlueTitan7]

"Pull straight up" as the guy clearly shakes them to come off ahahahahah

[@pigcityangelsoriginal2278]

the soundtrack.... Bob the Builder - Can We Fix It?

[@JoeTurmes]

YES. WE. CAN!

[@LesPaul209]

my music i used as background for this video ended at the exact same time as the video O_O

[@fabiolone70]

@etherreal777 yeah understand thank you.

[@atl3325]

Shouldn't he have used an oven MIT to handle those tubes? Ha, just kidding, I handle tubes with my hands too.

[@jspinks2388]

No WD40 is a lubricant..... You want a fast drying non-lubricating cleaner, Deoxit/LPS etc, the Lubricants will gum up the sockets, and as time goes by more dust gets attracted and further gums up and arcing nightmares can occur, Electrical cleaner and a small steel wool/pad to scrape contacts to remove the Oxidized layer.

[@JoeTurmes]

ha ha just did that last weekend....

[@djordjeblaga7815]

Best background music for this: kzbin.info/www/bejne/qYGQk6Jvpbp8pbs

[@rksguit]

I like how he removes the amp,on it's end,after that I was not that into it,due to the fact I have a "bought from new" JCM 800 or 2203,I really didn't like 900's[I tried one when they first came out],but playing distortion[not super clean-different instrument to me] guitar has become so common now,even 20 years ago,it was still kind of not unique,but not as insanely common,now,everyone and their pet Mongoose,can play Eruption,are rich,have Pro Tools or Cubase [on OSX of course-in Oz the base Mac Pro is a $4,800 no screen,no keyboard F.That] I'm fine with Atube 4 and a........anyway good luck tinkerers,and don't forget touching certain components,even after your amp hasn't been switched on for a week,can still kill you,be really careful!

[@Sleeckx]

maybe a little late, but no, definitely not!

[@nickvictor7398]

I thought silent films were replaced by talkies! Say something! I don't like to have to read along on my phone... text is too small!

[@VICTORFERREIA1987]

My god are $ 4,000 at stake

[@gregory5322]

My band-mate has the JCM 900. We replaced the tubes in it which needs to be biased. I turned to KZbin for pointers but alas, found an abundance of misinformation. First; DO NOT TOUCH THE GLASS! The oils on your fingers will dramatically reduce the life of the tubes. Second; you must check the voltage on every tube, not just one. If your tubes are mismatched you won't know unless you test them all. Last; I didn't learn anything I didn't know, including where to find the voltage regulator. Thanx

[@IronBroadsword]

You need to use rubber gloves or something when you handle the tubes. Oils from your fingers will reduce their lifespan

[@Sufferd666]

Then dust your house! :)

[@hsvdt]

why are you touching the power tubes with your bare hands! It can shorten the life of the valve because the oils on your fingers will heat up and give hot spots on the valve and issues can arise like warping or overheating.

[@Albee213]

I am trying to bias a JCM900 MKIII 2500 (50watt) and have some trouble. First off when I set my multi-meter to to 200ma it gives me a super low reading (11.7ma). When I set it to 200mv them it gives me a low reading. I turn the pot all the way up and max I can get is 27.2mv. What am I doing wrong?

[@JoeTurmes]

When you are measuring voltage, it needs to be in parallel to the circuit. When you are measuring current, the meter needs to be in series.