Is it time for new tubes? Bias and volume problem.

droosay · 02-09-2009, 01:01 PM

Hi. Could anybody help me with my problem. Ive got a Jcm 2000 tsl 100 and ive noticed lately that the volume is way too quiet. Ive had the amp on full at my band rehearsals and i can hardly here myself. Ive just done a bias test and what reading im getting on the right prong is 32.1 and the reading from the left prong is 52. Ive adjusted the mini pots and this is the highest readings i get. I cant get anything higher than that....Is it time for a tube change? Is so what tubes? The power tubes or preamp tubes. I hope im making sense.

Thanks.

zslane · 02-09-2009, 01:39 PM

Are all the tubes glowing a healthy orange color?

droosay · 02-09-2009, 01:44 PM

Yes they are glowing orange but not blindingly bright.

steelhorse · 02-09-2009, 03:03 PM

Check your bias first. It's really quite simple. All you need is a digital multimeter, a small insulated screwdriver, and some patience.

Check Euro Tubes for their how to bias video clips for the details.

If you can't dial in a good bias or if that doesn't help, then yes, a re-tube in the next move imo.

droosay · 02-09-2009, 03:52 PM

If the valves are dying would i reach a reading of around 90mv per channel?

American Viking · 02-09-2009, 04:24 PM

yeah dude, you need to be getting around 90mv per side. if you've been playing on it for a year or more it's about time to put in some new ones. make sure you buy a matched quad of EL34's or you can try KT77's, (little harder to find but lot of people say they sound pretty sweet). pop those bad boys in there and turn the trimpot until you can get 90mv per side. if you put the new tubes in there and still can't reach that, then there's a problem somewhere else. hopefully you can put new tubes in and be in good shape.
also you won't be able to get a perfect 90 per side but getting them pretty close is just fine.
YouTube - How to Bias a Marshall Tube Amp

steelhorse · 02-09-2009, 04:42 PM

Good question, I'm guessing probably not.

Check the bias before you do anything else. It sounds way way too cold and that's causing your volume issue imo.

Also if you are able to bias it between 85-90mV then I wouldn't just jump and do the power valves just yet. If you have or are able to get a few good pre amp tubes I would try those out first to see if that helps any.

But definitely your bias is way off according to the numbers you posted.

American Viking · 02-09-2009, 04:51 PM

+1

droosay · 02-14-2009, 12:33 PM

All sorted now. I Got some fresh EL34 tubes stuck those babbies in and then biased 90mv per side. The sound is so much better now with plenty of volume.

Thanks guys.

02-09-2009, 01:01 PM	#1 (permalink)
droosay Junior Member Join Date: Jan 2009 Posts: 6	Is it time for new tubes? Bias and volume problem. Hi. Could anybody help me with my problem. Ive got a Jcm 2000 tsl 100 and ive noticed lately that the volume is way too quiet. Ive had the amp on full at my band rehearsals and i can hardly here myself. Ive just done a bias test and what reading im getting on the right prong is 32.1 and the reading from the left prong is 52. Ive adjusted the mini pots and this is the highest readings i get. I cant get anything higher than that....Is it time for a tube change? Is so what tubes? The power tubes or preamp tubes. I hope im making sense. Thanks.

02-09-2009, 01:39 PM	#2 (permalink)
zslane Senior Member Join Date: May 2008 Location: Los Angeles, CA Posts: 367	Re: Is it time for new tubes? Bias and volume problem. Are all the tubes glowing a healthy orange color? __________________ JCM2000 DSL-100 head + 1960A 4x12 cab 30th Anniversary 6100 head JCM2000 DSL-401 combo Les Paul Standards ('96 Goldtop, '99 Ebony, '03 Honeyburst) Les Paul Custom ('04 Alpine White w/ gold hardware) Les Paul Supreme ('07 Trans Black w/ black hardware)

02-09-2009, 01:44 PM	#3 (permalink)
droosay Junior Member Join Date: Jan 2009 Posts: 6	Re: Is it time for new tubes? Bias and volume problem. Yes they are glowing orange but not blindingly bright.

02-09-2009, 03:03 PM	#4 (permalink)
steelhorse Senior Member Join Date: May 2008 Posts: 3,952	Re: Is it time for new tubes? Bias and volume problem. Check your bias first. It's really quite simple. All you need is a digital multimeter, a small insulated screwdriver, and some patience. Check Euro Tubes for their how to bias video clips for the details. If you can't dial in a good bias or if that doesn't help, then yes, a re-tube in the next move imo. __________________ www.ricojronline.com 760-956-6619 Garmopat Pedal Mods "I wouldn't mind hearing your head smash through a glass door. That would be cool..." luekmeyer

02-09-2009, 03:52 PM	#5 (permalink)
droosay Junior Member Join Date: Jan 2009 Posts: 6	Re: Is it time for new tubes? Bias and volume problem. If the valves are dying would i reach a reading of around 90mv per channel?

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02-09-2009, 04:24 PM	#6 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 2,031	Re: Is it time for new tubes? Bias and volume problem. yeah dude, you need to be getting around 90mv per side. if you've been playing on it for a year or more it's about time to put in some new ones. make sure you buy a matched quad of EL34's or you can try KT77's, (little harder to find but lot of people say they sound pretty sweet). pop those bad boys in there and turn the trimpot until you can get 90mv per side. if you put the new tubes in there and still can't reach that, then there's a problem somewhere else. hopefully you can put new tubes in and be in good shape. also you won't be able to get a perfect 90 per side but getting them pretty close is just fine. YouTube - How to Bias a Marshall Tube Amp __________________ Transformers inside amplifiers were not originally designed to be in there, and the tube was not created for the guitar amp. ANY recommended idle current is a guideline and in no way a necessary requirement. There is no skeleton key for any tube amp.

02-09-2009, 04:42 PM	#7 (permalink)
steelhorse Senior Member Join Date: May 2008 Posts: 3,952	Re: Is it time for new tubes? Bias and volume problem. Good question, I'm guessing probably not. Check the bias before you do anything else. It sounds way way too cold and that's causing your volume issue imo. Also if you are able to bias it between 85-90mV then I wouldn't just jump and do the power valves just yet. If you have or are able to get a few good pre amp tubes I would try those out first to see if that helps any. But definitely your bias is way off according to the numbers you posted. __________________ www.ricojronline.com 760-956-6619 Garmopat Pedal Mods "I wouldn't mind hearing your head smash through a glass door. That would be cool..." luekmeyer

02-09-2009, 04:51 PM	#8 (permalink)
American Viking Senior Member Join Date: Jan 2009 Location: RICHMOND, VIRGINIA Posts: 2,031	Re: Is it time for new tubes? Bias and volume problem. +1 __________________ Transformers inside amplifiers were not originally designed to be in there, and the tube was not created for the guitar amp. ANY recommended idle current is a guideline and in no way a necessary requirement. There is no skeleton key for any tube amp.

02-14-2009, 12:33 PM	#9 (permalink)
droosay Junior Member Join Date: Jan 2009 Posts: 6	Re: Is it time for new tubes? Bias and volume problem. All sorted now. I Got some fresh EL34 tubes stuck those babbies in and then biased 90mv per side. The sound is so much better now with plenty of volume. Thanks guys.

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