I sold a DSL 100 to a good buddy years ago. He brought it to me because it’s not running. Found a fuse issue. I had forgotten how easy it is to bias these amps. Thanks for the refresher. Well done video.
Wow 4th video on tude amp repair and bias...finally some1 finally shows the how to..been wanting to repair my dsl 100..Everyone opens head points and talks about doing the bias but not one did the simple step u did..what i needed.. Thanks for the brief but detailed info get me over the hump.
This is an excellent video, and exactly what I needed as try my hand on a Marshal TSL 602. I appreciate that you pointed out important safety concerns. I notice you specified that the guitar must be plugged in - this suggests to me that the impedance of the input is an important consideration. I recently placed a G-system effects processor in my signal chain between the guitar and the input to the amplifier. Soon after, I observed the symptoms of bias voltage drift. I'm thinking right now that my bias voltages were adjusted at the factory using typical guitar input impedance; now that I have introduced the G-system, those bias voltages are out of tolerance. Thanks for sharing!
You have indeed helped me out. I'm glad to see that the DSL isn't too complicated or risky to bias at home. Thanks for the video and keep rocking mate.
Actually, 85-90mv is kinda high, and will give you 35-45 milliamps per tube (the safe operational range of EL34 is 10-40mA per tube), so adjusting the millivolts to 75-80mv will actually give the amp more headroom and the amp won't tend to turn to mud with the volume cranked.
Scott Dunn .... You are correct . 90 is too high . 70 per side is safe , sounds great and gives good tube life . Too many think biasing hot is good ..... its not . Also , watch out for crazy bias drift on these early DSL amps ! Also , I recommend playing the amp at decent volume for at least 10 minutes to stabilize and warm the power tubes better before biasing . Then check bias again after at least half hour of run time for a better bias reading . Dont want to bias a cold DSL amp .
@@leftygtrplr6184 Well if that's what Marshall have it set to, that is what it should be set to! The trim pots will turn down to no lower than 37mV with most tubes.
I have heard other people say that setting your bias effects speaker breakup. A higher setting is supposed to make it not break up as early. I’ve also heard that a slightly lower bias can increase tube life. I can’t confirm either one of those theories though. As far as an audible sonic difference is concerned, I doubt there is much at all. My amp sounded fantastic even when I unknowingly played it with the tubes out of whack.
Yes there is a difference. A colder bias will be fine though and yes many manufacturers like peavey intentionally set the bias cold on fixed bias amps so the tubes can last a long time. As far as a difference in tone there is that as well, the amp can sound a bit lifeless with a colder bias in my experience. However on a JCM 2000 I like colder bias.
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?
Great video! I bought a used JCM 2000 a few years ago and I get a lot of hum and hiss when I power it on. It does work, but I dont know if the tubes are shot. Im a bass player, but use a Marshall half for messing around at home. I also have a bunch of bad pots and was thinking of replacing all the pots, buttons and tubes. Is it worth it or should I buy a new one?
Yes. I can’t be positive that is the problem, but I always start with the tubes. The 4 larger tubes are the power tubes. Replace those as a matched set. The smaller tubes are the preamp tubes. After you replace the power tubes, you can check each preamp tube individually by lightly tapping on each one. If one of them makes an odd noise it is most likely the problem preamp tube. You can replace one preamp tube at a time.
Possibly. Although could just be biased really cold. I got a second hand DSL 50 just recently and it sounds wicked, lots of gain. Although for really high gain stuff, it does benefit from a tube screamer or SD1.
Great video but I'm curious, are those gold lion kt-77's in there? I'd so what do you set the bias to? In using the jj kt-77's myself and it really feels like 90 is too damn hot
I set mine to about 87. I’m going to re do mine pretty soon and try a little lower and see how they sound. I had a few people comment that they sound better set a little lower. I’m going to start about 80 and go from there.
I didn’t. I’m not sure if you’re supposed to, but mine works fine without doing that. I did go back and bias them a lot less after someone suggested that in the comments. I set them under 50
It looks to me like you have a revised main pcb or something . I had to replace mine due to bias drift on my JCM 2000, 2005 model year. Installed a classic tone Output Transformer and choke as well.
I heard marshall fixed the bias drift issues after 2003. The material the old boards were made of became conductive after get hot. Also i heard this only happens to the 100 watt models? I had two 50 watters with no issues.
@@Briman24 well mine had very bad bias drift and it had the old board material and I believe mine was a 2005. I heard they fixed it as well but I am always curious of that since mine still was bad. The tubes would red plate and the bias would slowly creep up as it warmed up so high the bias pots were unable to go any lower or any higher depending on how warm it was. With the new board and tubes now it is stable after sitting for 30 minutes or so. Some amps may still have bias drift but owners dont notice it as some of the tubes are fairly robust (previous owner did not notice it and the jjs were so bad the logo and the tube was physically burnt looking but the amp sounded fine for the most part) the previous owner was the original owner and had no idea 🤷♂️ but did mention tube failures. You may come across one that doesn’t have it im unsure whether they exist as i only have had this one
I must have misunderstood something. If after the initial check you're playing and everything sounds good.....why would you be going back a 2nd time to adjust again? If it ain't broke don't fix it, right?
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I sold a DSL 100 to a good buddy years ago. He brought it to me because it’s not running. Found a fuse issue. I had forgotten how easy it is to bias these amps. Thanks for the refresher. Well done video.
Wow 4th video on tude amp repair and bias...finally some1 finally shows the how to..been wanting to repair my dsl 100..Everyone opens head points and talks about doing the bias but not one did the simple step u did..what i needed..
Thanks for the brief but detailed info get me over the hump.
Hey Jim, I’m glad you found some useful information here. Thanks for the feedback.
This is an excellent video, and exactly what I needed as try my hand on a Marshal TSL 602. I appreciate that you pointed out important safety concerns. I notice you specified that the guitar must be plugged in - this suggests to me that the impedance of the input is an important consideration. I recently placed a G-system effects processor in my signal chain between the guitar and the input to the amplifier. Soon after, I observed the symptoms of bias voltage drift. I'm thinking right now that my bias voltages were adjusted at the factory using typical guitar input impedance; now that I have introduced the G-system, those bias voltages are out of tolerance.
Thanks for sharing!
There are really few close to none videos about how to bias tubes in a JCM2000, thank you for uploading this video!
You’re very welcome
You have indeed helped me out. I'm glad to see that the DSL isn't too complicated or risky to bias at home. Thanks for the video and keep rocking mate.
Thank You for the positive feedback, and thank You for checking out the video.
@@jayjohnson4352 Thanks Jay. So turning those trim pots to right decrease the voltage? not to the left?
Simple, easy, straight to the point, thx!
Excellent! Straight to the point. 👍🏼
I wish all amps were as easy to bias as this one is.
Seems very easy to bias, i will keep mine, it sounds very good too! Thanks for a very good video!
Actually, 85-90mv is kinda high, and will give you 35-45 milliamps per tube (the safe operational range of EL34 is 10-40mA per tube), so adjusting the millivolts to 75-80mv will actually give the amp more headroom and the amp won't tend to turn to mud with the volume cranked.
I took mine down to 55 and LOVE it. I have a choke and OT from classictone
Scott Dunn .... You are correct . 90 is too high . 70 per side is safe , sounds great and gives good tube life . Too many think biasing hot is good ..... its not . Also , watch out for crazy bias drift on these early DSL amps ! Also , I recommend playing the amp at decent volume for at least 10 minutes to stabilize and warm the power tubes better before biasing . Then check bias again after at least half hour of run time for a better bias reading . Dont want to bias a cold DSL amp .
The Marshall Service bulletin listed the bias as 90 mV for the JCM 2000 DSL 100 (and 45 mV for the DSL 50). I was surprised by that also.
@@leftygtrplr6184 Well if that's what Marshall have it set to, that is what it should be set to! The trim pots will turn down to no lower than 37mV with most tubes.
We do ours at 70mv
super nice and cleanly done. Great video/
Thanks, Brotha. Short and sweet. What sonic differences do higher volt values, within range, make?
I believe tubes that are run too hot sound muddy and indistinct. Colder biases sound weak and thin.
Thanks, I was looking for exactly that 😊👍
Very informational I like the video
Thank You Benny. I appreciate the feedback
I have heard other people say that setting your bias effects speaker breakup. A higher setting is supposed to make it not break up as early. I’ve also heard that a slightly lower bias can increase tube life. I can’t confirm either one of those theories though. As far as an audible sonic difference is concerned, I doubt there is much at all. My amp sounded fantastic even when I unknowingly played it with the tubes out of whack.
Yes there is a difference. A colder bias will be fine though and yes many manufacturers like peavey intentionally set the bias cold on fixed bias amps so the tubes can last a long time. As far as a difference in tone there is that as well, the amp can sound a bit lifeless with a colder bias in my experience. However on a JCM 2000 I like colder bias.
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?
I had that problem with a dsl 40c. I replaced the pre amp tubes one by one. One of the pre amp tubes were bad and caused the problem.
Great video! I bought a used JCM 2000 a few years ago and I get a lot of hum and hiss when I power it on. It does work, but I dont know if the tubes are shot. Im a bass player, but use a Marshall half for messing around at home. I also have a bunch of bad pots and was thinking of replacing all the pots, buttons and tubes. Is it worth it or should I buy a new one?
I would start with the tubes
@@jayjohnson4352 Can that cause a loud hum/hiss?
Yes. I can’t be positive that is the problem, but I always start with the tubes. The 4 larger tubes are the power tubes. Replace those as a matched set. The smaller tubes are the preamp tubes. After you replace the power tubes, you can check each preamp tube individually by lightly tapping on each one. If one of them makes an odd noise it is most likely the problem preamp tube. You can replace one preamp tube at a time.
Thank you buddy,helpfully!
I have that very exact amp but don't really have the high gain without a pedal ? Do you think i need new tubes?
Possibly. Although could just be biased really cold. I got a second hand DSL 50 just recently and it sounds wicked, lots of gain. Although for really high gain stuff, it does benefit from a tube screamer or SD1.
Great video but I'm curious, are those gold lion kt-77's in there? I'd so what do you set the bias to? In using the jj kt-77's myself and it really feels like 90 is too damn hot
I set mine to about 87. I’m going to re do mine pretty soon and try a little lower and see how they sound. I had a few people comment that they sound better set a little lower. I’m going to start about 80 and go from there.
I saw somewhere to turn all pots to zero. Any need for that?
I didn’t. I’m not sure if you’re supposed to, but mine works fine without doing that. I did go back and bias them a lot less after someone suggested that in the comments. I set them under 50
But, do I have to bias this Marshall when changing for the same valves? (EL34 JJ)
Yes. Every tube is unique.
It looks to me like you have a revised main pcb or something . I had to replace mine due to bias drift on my JCM 2000, 2005 model year. Installed a classic tone Output Transformer and choke as well.
I didn’t change anything. I bought it new.
@@jayjohnson4352 you must have one of the later ones? Or maybe some are unaffected
I heard marshall fixed the bias drift issues after 2003. The material the old boards were made of became conductive after get hot. Also i heard this only happens to the 100 watt models? I had two 50 watters with no issues.
@@Briman24 well mine had very bad bias drift and it had the old board material and I believe mine was a 2005. I heard they fixed it as well but I am always curious of that since mine still was bad. The tubes would red plate and the bias would slowly creep up as it warmed up so high the bias pots were unable to go any lower or any higher depending on how warm it was. With the new board and tubes now it is stable after sitting for 30 minutes or so. Some amps may still have bias drift but owners dont notice it as some of the tubes are fairly robust (previous owner did not notice it and the jjs were so bad the logo and the tube was physically burnt looking but the amp sounded fine for the most part) the previous owner was the original owner and had no idea 🤷♂️ but did mention tube failures. You may come across one that doesn’t have it im unsure whether they exist as i only have had this one
@@resistorstudios are you 100% sure it was a 2005? Yours is the first one i have heard of for a 50 watt and a 2005! Bizarre
Made EAZY THANKS
Thank you man!! Really helpfull!
Thank You for the feedback.
I must have misunderstood something. If after the initial check you're playing and everything sounds good.....why would you be going back a 2nd time to adjust again? If it ain't broke don't fix it, right?
Just in case after the tubes break in a little after warming up. The closer they are to being biased correctly, the longer they should last.
@@jayjohnson4352 Had no idea there was a break in period for tubes, thanks
easy to access bias probe points should be a standard feature of every amp honestly.
What about a JCM 2000 DSL 50w with only 2 power tubes? What would the ideal bias rating (per tube) be? I keep hearing that 38mv would be optimal?
I would try a few different settings and see how it sounds. I would definitely keep it 45 and under.
@@jayjohnson4352 great advice
I use alligator clips on the pins. Easier to just work with the bias knob that way and watch your multimeter.
Cheers man.
Those look like KT-77's not EL-34's. You don't need a guitar plugged in to bias. Also 90 is too high, 80mv per side is plenty hot.
69/70 is the perfect bias for JCM 2000 DSL 100 88 is way way to high ..
Plug ins? really?
Skull ☠️ yeah hoss. Use a metal screwdriver 🥴🥴