How to Bias Marshall JCM2000 DSL Guitar Amplfier

[@lightinme217]

Such good info! I just picked up one of these 1-16-2023 used and my first step is to replace the power section tubes and bias the amp. So glad this is easy to do! Thanks do much for your time teaching!

[@stuartukguitarampguy5830]

Thanks Matt I'm glad you enjoyed it.

[@russellmootz7690]

Holy cow! Thanks man. That was so easy and I feel so much better now. Mine were runnin' at 85 milivolts each side. I recently blew a fuse and tubes.

[@stuartukguitarampguy5830]

Great. Yes 85 is way too hot!

[@GoldSeals]

I also have Jcm 2000 dsl100.I spent hours and hours trying to solve the bias drift problem.I bought my amp back in 2000.It was a 1998 model according to the serial number.It was still under warranty back then.Im located in the US.I took it to an authorized service center and they couldnt fix the problem.They called me a couple of months later to come pick it up.Having had a background in electronics I chose to tackle the problem.I finally gave up after awhile,and just put the amp away and bought another brand.A couple of years later I was missing playing my marshall amp.So I bought another one in 2003.It turns out that was on the list too of developing a bias drift problem.But the bias never went over 100mv even though I set it to 90.Eventually I was able to purhase a new mainboard and that solved my drifting problem.I also later bought another main board for the 2003 model,but never put it in.

[@stuartukguitarampguy5830]

Thanks for sharing that. It was a MAJOR issue for Marshall which affected other models too.

[@tjsogmc]

New Ampegs have a LED light and bias pot on the back of the amp. You simply turn the adjuster with a small screwdriver until the light turns green. That's it, job done :)

[@stuartukguitarampguy5830]

Yes. I'm never totally happy with those digital LED bias arrangements though. I'm sure they're fine. One problem is the bias current isn;t really THAT critical, and if a customer sees a red LED or whatever, they start to panic and think the amp is about to blow. It's a good job most guitarists are blissfully unaware of the state of bias of their tubes!

[@tjsogmc]

@@stuartukguitarampguy5830 I agree. The same with their tube life. I wonder if they know that most tubes will last 15 or 20 years under normal use? Nevermind, let the tube vendors make them think they have to change them every 6 months- it's good for the economy.

[@rickycompton2610]

Great video Stuart got to love all this great knowledge thank you for all your time and videos.

[@stuartukguitarampguy5830]

Thanks Ricky!

[@zbaby82]

I have two Marshall TSL60 amps and they're very easy to bias. I wish all amps were as easy to bias as them. It's a hassle to take a chassis out of its shell just to bias the tubes.

[@stuartukguitarampguy5830]

Agreed!

[@ulfb5467]

Hi Zack. I want to change valves on my TSL60, do you know the correct bias setting. Can you also recommend any power tubes, thought to buy from Thomann? Cheers from Stockholm

[@christopherhampson265]

Thankyou ! Very informative and simple to follow. I've just bought tsl 602 with a poorly output transformer and the previous chap who owned it put new JJ s in to try to fix it as the valves wouldn't light up but I think the windings for the plate heater are giving too much voltage and blowing the fuse hiding on the pcb . Also the tx looks like it's got a bit warm !!!!! Nowhere can i find the secondary voltages for the 2005 dagnall tx !! I've found the schematics but they show the position of tx but no voltages ! Is there anybody out there that can help ? I would love to make it sing again ...... Cheers...

[@SonicSoundofDoom]

So, during this video you had a cabinet connected and the power on right? I saw that people are not recommending JJ’s for the head, what EL34’s would you recommend? Thanks!

[@stuartukguitarampguy5830]

Hi Not 100% sure what you meant there. I had the power on of course. No cab connected, that's not needed. Yes don't use ordinarly JJ EL34 for this head or any 100W Marshall head. Use EL34II from JJ or MARSHALL EL34 are also good. Not sure if you are in UK but Watford valves sell the Marshall EL34

[@joonasvuomajoki2636]

​@@stuartukguitarampguy5830 well that's not correct. You had some sort of load in it. You can't turn a valve amp on with no load.

[@stuartukguitarampguy5830]

@@joonasvuomajoki2636 Who told you that? You shouldn't PLAY through an amp with no load connected (because there's a very small chance the output transformer could be damaged) but it's ok to have it running e.g. to bias it.

[@joonasvuomajoki2636]

@@stuartukguitarampguy5830 really? That's news for me.

[@stuartukguitarampguy5830]

@@joonasvuomajoki2636 It's an understandable mistake as the injunction is "Dude! Don't run your amp without a cab connected!!!" If you want a more detailed explanation let me know.

[@barron267]

Excellent video, thank you

[@stuartukguitarampguy5830]

Thanks Steve

[@Kindoflikerambo]

Thank you x2!

[@RobAndKim444]

Thank you very much Stuart, it's so nice to do your own biasing, I just purchased a 2005 JCM 2000, (100w) over the Internet previous owner said the head needed absolutely nothing,, i just finally ID'd the tubes, definitely the stock tubes (4 x winged C SED, and 4 x Marshall preamp mystery tubes) although there appears to be some life left in all of them, do you think that these dinosaur tubes would affect the tone, overly bright tone ? (bias is 72 evenly), I'd appreciate if you can give me your opinion on that, I read that some owners like to remove the bright cap because of the bright tone

[@jeffjohansen3458]

The videos that you have done on the JCM 2000 amp have been super helpful in getting my amp back to tip top shape. One question that I have for you: Have you ever dealt with these amps having issues with a lot of extra noise when using the effects loop? If so, do you know of a good solution to that problem? Thanks for all that you do.

[@stuartukguitarampguy5830]

Hi Jeff Thanks for the feedback. No, I havenlt come across that before, sorry.

[@gtyler7451]

I just replaced the main board on my DSL100 (original late 90's issue) because of the bias drift problem and I got each side around 70.5mv but i was originally using the 90 per side Marshall setting. Isnt that gonna kill the tubes quicker ? The gain seemed to turn mushy as well when it was all the way up. I was blowing HT fuses as well but that could have been the drift issue causing that which seems to be gone now. Thanks for the video!

[@stuartukguitarampguy5830]

My view is that there's very litle difference between 35mA per valve and 45mA. I don't believe it's possible to hear a difference. So I'd go for the 35mA. As you say, it will make the valves last a bit longer. It won't blow HT fuse at 45mA per valve so I agree, that was probably the drift issue.

[@henryssurfshowcase]

Thank you! Question: is it bad for amp to run as far off bias as that one was? Just not the best sound? Or could it damage amp?..

[@stuartukguitarampguy5830]

If the amp is biased very cold it will sound a bit 'thin'. If it is biased a bit hot it will sound quite good. If biased too hot, the life of the valves is impacted, also it may cause a problem such as blowing the HT fuse.

[@henryssurfshowcase]

Hi Stuart, does it matter if I bias amp with a cabinet load of 8 ohms or 16. will it sound basically the same for both?

[@stuartukguitarampguy5830]

@@henryssurfshowcase Hi Henry The bias is not affected by the speaker load. You can actially bias an amp without a speaker connected (although it's better to have one connected for reasons I won't go in to).

[@green461]

AC or DC setting? What is plugged into the instrument jack? What is the amp set on? the lower the bias reading which is hotter or colder ? higher or lower?

[@stuartukguitarampguy5830]

Hi. It's been a while since I did this amp so cannpt answer your questions directly. However, I can tell bt the way they are framed that you have some misconceptions about biasing. If you have any questions you want me to clear up, please ask them. All the best.

[@heythere6983]

Can you explain something to me, I have a few tube amps and some have four power tubes . Do all four tubes have to be matched together? Or is it, one matched pair and another matched pair? Iv seen some people say matching tubes isn’t totally important , worst case is tubes burn out a bit faster or the sound isn’t super even? I’m trying to stock up on some tubes for my amps but need to figure out the basics . I also just got a bogner and it turns on and makes no sound whatsoever . I have no idea what’s going on with that amp. But anyways yeah, I mean could I technically buy single tubes and still bias them properly? How does their plate voltage come into play with bias? Too high voltage means they can’t bias lower? I think I had an issue with some ruby tubes where I had to bias an amp high since the tube couldn’t go lower itself . This stuff is a bit confusing , I actually think I prefer lower gain in general and more of a crunch and less saturation . But could you answer some of these questions for me? I really need to figure out how to narrow down what tubes to get and what to look for. I’m not sure if I can just get any el34s for my marshalls or they need to have a certain rating to bias properly? I can’t seem to find answers to these questions online , I guess because they are so basic lol. Any help? I’d really appreciate thanks

[@stuartukguitarampguy5830]

Hi. Okay without writing an essay, here's some stuff. So, ideally you should have a matched quad, that makes life easy. However as long as BOTH halves of the push-pull amplifier match, that's okay too. So let's say you had two pairs of valves, 2 at 25 (units don't matter for this example) and 2 at 15. Let's also assume that V1 and V2 are one pair and V3 and V4 are the other pair (this is usually the arrangement). So you would put valves in like this: V1: 25 V2: 15 V3: 25 V4: 15 So each pair adds up to the same (40 in this exmple). Does that make sense? Next, the two things which affect bias current for a given valve are plate voltage (higher plate voltage, more bias current, unsurprisingly) and grid voltage. This is a negative grid voltage, so the more negaitive the grid, the less current flows through the valve. Adjusing the bias involves adjusting this negative grid voltage (usually by a pot) until the bias current is right. You can't adjust the plate voltage, so that's a given. If you don't match the valves (just bung anything in) then one or more may run quite hot, shortening the life of those valves, sometimes dramatically. Also you will get a bit more distortion on the signal as the PUSH half is (say) stronger than the PULL half. Kst guitarists couldn't care less about a bit more distortion and may even life it. Check out my 3 videos entitled 'How Guitar Amplifiers Work' Parts 1,2 and 3 All the best Stuart

[@clementmorin4962]

Thank you !

[@DrWatts-bi1jv]

Factory spec is 90mV per side - believe it or not! Volume set to minimum... I usually set em for 80/85 and NEVER EVER use JJ's in a DSL100 or TSL100. They can't take the high HT and fair quick smart! Good video Stu!

[@stuartukguitarampguy5830]

Thanks Yes I like to bias a bit cool. Totally true about JJs in these DSL and TSL. I would never fit them, but customer wanted to retain. They'll PROBABLY be okay....

[@GoldSeals]

Thanks for the info about the JJ tubes

[@henryssurfshowcase]

Where do you think JJ's are best set on Marshal TSL? Maybe 75? i have had good luck and sound on my TSL with JJ's. Especially for the price, but never had biased it myself..

[@marshall401]

I've owned a tsl 100 for the last 20 years, the only valves that work properly in it are winged C, JJs just blow up straight away. Biased at 80mv per side.

[@KaddysJamKave]

Wow that's really easy to Bias... are there any other amp heads you know of that is THIS easy to bias without taking the chassis out? I'm always hesitant to buy amps that require biasing but I wouldn't mind doing this.

[@stuartukguitarampguy5830]

Hi unfortunately 99% of amplifiers require you to pull the chassis. It's almost as if... and hear me out... the manufacturers don't want guitarists sticking screwdrivers in and cranking up the bias so the valves are cooked then send it back under warranty....

[@KaddysJamKave]

@@stuartukguitarampguy5830 haha that is true... Perhaps they prefer idiots like me to then take the risk without knowing what I'm doing and electrocute themselves instead hehehehe 😂

[@thomasmogensen1]

Nice little video 👍🏻 Do you bias 6l6gc at about 35 mV par tube as well?

[@stuartukguitarampguy5830]

Hi Thomas It depends on the plate voltage but yes 35mA-40mA is about typical.

[@thomasmogensen1]

@@stuartukguitarampguy5830 yes of cause i see , thanks for the answer. Do you have any video on a dead peavey 112 vk ? Cause i have one that just died on my friend, i will not even turn pilot light on?? Thanks alot Thomas

[@stuartukguitarampguy5830]

@@thomasmogensen1 Hi Thomas. No videos on that. Should be fairly easy to diagnose. See if mains is getting to the mains transformer and work from there.

[@thomasmogensen1]

@@stuartukguitarampguy5830 thanks 👍🏻 I did that , getting 250 ish, on both hw, 15 volt on 1 LW and zero on the other LW. And 80 volt on bias. ? Is that normal? The input trans, was very hot 15 min after it shut off, noticed that the power valves was glowing blue?

[@stuartukguitarampguy5830]

@@thomasmogensen1 What do you mean by HW and LW? You may have had a faulty valve arcing over. That could have caused excessive current. MEasure AC voltas on the primary and secondaries. If you're getting 240 or so on the primary (measured direct on the transformer leads) and no volts on one or more of the secondaries then you transformer is suspect. Good luck.

[@garyferris7185]

Please state what the Amp is on or off or on standby, I know the speaker needs to plugged in, thanks.

[@stuartukguitarampguy5830]

To check bias the amp needs to be out of standby. The speaker doesn't need to be plugged in but you can if you want to.

[@psychic_records]

@@stuartukguitarampguy5830 wait shouldnt there be a load plug in at all times??

[@stuartukguitarampguy5830]

@@psychic_records No not needed. Only a precaution if you're going to put a signal through the amp. No signal? You don;t need the speaker connected.

[@psychic_records]

@@stuartukguitarampguy5830 I've never heard this and I think recommend everyone connect a speaker load regardless. Seems to be tube amp 101. But thats just me.

[@stuartukguitarampguy5830]

@@psychic_records Yes it's better just to slavishly do it rather than thinking it through each time. FYI the reason is can be a problem is as follows. Amp is on, guitar connected, speaker disconnected. Amp turned up very loud. Really strong chord played on guitar. This results in a big signal at the primary of the output transformer. As the seconday is not loaded this can result in a really big signal appearing on the secondary. Under certain, very rare circumstances, this can cause an arc (short) in the output transformer windings and damage it. Super rare and it needs those exact conditions above. So, no guitar attached? No need to have a load attached. But, as I say, feel free to do it as a precaution.

[@TheCleaner6969]

I have a 50w & I'm getting a cutting in & out like a bad cable. Over the last year when I turn the amp off I hear a glass ping when cooling down. I'm thinking a preamp tube is going out although it's not losing volume when it's on & the cutting in & out like a bad cable stops. I take it that I would just ground multi-meter & turn both screws to match between 38 & 45 as Marshall recommends as you did here?

[@stuartukguitarampguy5830]

Yes just follow what I did on the video. Centre pin is ground.

[@TheCleaner6969]

@@stuartukguitarampguy5830 I checked all the tubes & they seem fine. I also baised the amp but it crackled the other day again & it kinda seems like a noise gate which I don't have. I was plugged straight into the amp. The amp noise got quieter & then when I strummed harder it came back after cutting out but seems less noisy. I did use a A/B/Y I built that's on my channel for about 3 minutes to use 2 guitars & that's when this started.

[@stuartukguitarampguy5830]

It could be a few things I'm afraid, you'll need to get it looked at it seems.

[@TheCleaner6969]

@@stuartukguitarampguy5830 I don't have any techs in my area.

[@stuartukguitarampguy5830]

Whereabiuts are you?

[@bengordon7635]

I have the tsl combo and the spec is 90 thats how I bought my tsl head new it was 90 mv ,, I bought the new 20rev board and my god a new amp ,, if i try to run under 90 it sounds terrible and over 93 sounds terrible ...

[@stuartukguitarampguy5830]

Not sure if you like it or not from your comments?

[@androidgameplays4every13]

I own a JCM2000 DSL50 with only 2 power EL34, is the same procedure? or there is only 2 pins instead of 3?

[@stuartukguitarampguy5830]

Same from memory but I don't have the info to hand.

[@androidgameplays4every13]

@@stuartukguitarampguy5830 I can confirm the 50W version has 3 pins too, today I removed the "rear grill", this video gave me the courage to bias my amp for the first time after 10+ years of owning it, thank you! The next step would be to take the chassis out, is there a video where you show how to remove the chassis? it's a little bit intimidating for a beginner like me to just go and remove it, this head is so heavy, I feel I need to know what to do before attempting it. Thank you very much for sharing these videos, they are priceless for me.

[@stuartukguitarampguy5830]

@@androidgameplays4every13 Hi Well done on the biasing! The chassis is easy, just put the amp up on its end, remove the 4 screws on the bottom and slide the chassis out.

[@jamesprice6381]

HORRIBLE design IMHO, the mere FACT they DRIFT against ea other is PROF, why not just ONE pot n ONE resistor? These amps fail they usually fail BIG time, no gttg @ it! ive teched over 30 years def NOT my fav amp ta wk on, ive had ta take HOLLOW drills over the pin #5 n solder direct to bias resistor due to the boards becoming inductive n passing current! Also one these amps, w/upside down n front facing you SOME have a 47 or 500pf on FAR RIGHT of power tube board over by last pwr tube, THSES caps can either LEAK, or short n cause damage i REMOVEM... Plate to grid if im not mistaken! Engineering at its finest! :)

[@stuartukguitarampguy5830]

YEs agreed. I've taken many a boardd out using my 26-point checklist! What could possibly go wrong with having 200+ interboard connection points???