Marshall DSL tube question

[mrp5150]

I just bought some new tubes for my DSL from Doug's Tubes and wanted to double check whether I can just put the new power tubes in (matched quad of JJ EL84's) without messing with the bias or anything? Doug said I can just put the new ones in with no problems, but I wanted to double check so I don't fuck anything up.

 

[D-Rock]

EL84's??

Only the DSL 401 combo takes those.

 

[Gainfreak]

I just bought some new tubes for my DSL from Doug's Tubes and wanted to double check whether I can just put the new power tubes in (matched quad of JJ EL84's) without messing with the bias or anything? Doug said I can just put the new ones in with no problems, but I wanted to double check so I don't fuck anything up.

Doug Might have given you tubes that will run in a bias range that will work for the amp but Id definitely bias the amp if you know how to. I don't think the Marshall 401's are a fixed bias like the boogies are.

 

[MrDan666]

The DSL has external bias points right? If so, and if you have a Digital Multimeter then definitly check the bias at the very least. It could be close or way out, who knows!

 

[mrp5150]

He told me that, "No bias adjustment is possible without changing resistors." Not exactly sure what that means. I've never changed power tubes in anything except a Mark III combo.

 

[MrDan666]

He told me that, "No bias adjustment is possible without changing resistors." Not exactly sure what that means. I've never changed power tubes in anything except a Mark III combo.

Hmm i dont really know much about the DSL combo, but i have a TSL60 head here which has an adjustable bias via a trim pot in the back panel of the amp. All you do is read the bias off the two pins in the backpanel with a DMM and then adjust the trim pot as needed...

But like i said, iv no idea if thats how the DSL combos work

 

[1big1]

if it's a dsl 401 it's an el 84 based power section. you should just be able to pop in the new power tubes and away you go. el 34's are adjustable bias.. el 84's typically are not. in the majority of el 84 based power sections the bias is set by a resistor.. so no bias adjustment is necessary. plug and play. give them about ten or so hours of playing time and they should open up sound-wise.

 

[Gainfreak]

if it's a dsl 401 it's an el 84 based power section. you should just be able to pop in the new power tubes and away you go. el 34's are adjustable bias.. el 84's typically are not. in the majority of el 84 based power sections the bias is set by a resistor.. so no bias adjustment is necessary. plug and play. give them about ten or so hours of playing time and they should open up sound-wise.

Im a tool lol!! I thought he said el-34 not el-84 tubes!!


Listen to this man

 

[1big1]

it's really easy to figure out the difference. an el 84 has a small nine pin base.. the el 34 has the large eight pin base.

 

[mrp5150]

if it's a dsl 401 it's an el 84 based power section. you should just be able to pop in the new power tubes and away you go. el 34's are adjustable bias.. el 84's typically are not. in the majority of el 84 based power sections the bias is set by a resistor.. so no bias adjustment is necessary. plug and play. give them about ten or so hours of playing time and they should open up sound-wise.

Cool, thanks man!

 

[Gainfreak]

if it's a dsl 401 it's an el 84 based power section. you should just be able to pop in the new power tubes and away you go. el 34's are adjustable bias.. el 84's typically are not. in the majority of el 84 based power sections the bias is set by a resistor.. so no bias adjustment is necessary. plug and play. give them about ten or so hours of playing time and they should open up sound-wise.

I used to think that all EL84 amps were this way, but it seems that they're not (I know, you said "typically".) Anyone know why most EL84 amps don't have an adjustable bias?

I think it has to do if the amp is cathode biased or not. If it is wired for a cathode bias then the tube will self bias itself, If it is not a cathode bias then I guess it will have an adjustable pot.

 

[1big1]

if it's a dsl 401 it's an el 84 based power section. you should just be able to pop in the new power tubes and away you go. el 34's are adjustable bias.. el 84's typically are not. in the majority of el 84 based power sections the bias is set by a resistor.. so no bias adjustment is necessary. plug and play. give them about ten or so hours of playing time and they should open up sound-wise.

I used to think that all EL84 amps were this way, but it seems that they're not (I know, you said "typically".) Anyone know why most EL84 amps don't have an adjustable bias?

I think it has to do if the amp is cathode biased or not. If it is wired for a cathode bias then the tube will self bias itself, If it is not a cathode bias then I guess it will have an adjustable pot.

bingo!

 

[blackba]

The DSL401 does have a bias pot, there are 3 test points, you just set your meter to millivolts. not sure exactly where to set it, but I did bias my DSL401 when I had it many years ago.

Don't assume all EL84 amps are cathode biased, the peavey classic 30 is fixed bias, but has no pot. Just like the 5150 they failed to put a bias pot on the amp.

 

[mrp5150]

I have no clue how to bias an amp.

 

[blackba]

I have no clue how to bias an amp.

Do you have a digital multimeter, if so you just need to find the con1 connector, and measure the voltage and then just a small screw driver to adjust the pot, only problem is I don't know where to set it. If you get a multimeter and snap a picture of the guts I can walk you through it....

 

[mrp5150]

I have no clue how to bias an amp.

Do you have a digital multimeter, if so you just need to find the con1 connector, and measure the voltage and then just a small screw driver to adjust the pot, only problem is I don't know where to set it. If you get a multimeter and snap a picture of the guts I can walk you through it....

No, I don't have one of those. The amp is back home where I don't have a computer as well. Sounds like I won't need to bias it though. I'll have to email Doug again and double check with him.

 

[blackba]

When I biased mine, I set it as warm as it would go and it still was cold, so you will probably be alright. There is a document floating around that has the instructions for the marshall JCM2000 series amps....

 

[BenoA]

Hope this can help:

Video of biasing a DSL:

http://www.eurotubes.com/euro-Marshall-DSLTSLV.htm

Here's the Marshall Service Bulletin on biasing the JCM2000 series amps:

Procedure:
1. Make sure the amp is connected to a load with the proper impedance selected.
2. Power up amp on Standby, and let the circuit stabilize for a couple of minutes.
3. Locate the male three pin molex connector (CON2) with the two mini pots (PR1 and PR2) (located on each side of the molex connector) on both ends found at the bottom of tube bay.
4. Connect DMM (set to read mV) with alligator leads, reference common lead to center pin (pin2) on molex connector CON2 and positive lead to pin1 on CON2.
5. Take amp off Standby with no signal, adjust mini-pot (PR1) closest to pin that the positive lead from your DMM is connected to and set it to mV voltage that is listed below.
6. Repeat steps 4 & 5 for pin3 mV and until pin1 & pin3 mV readings are the same.

Bias Settings:
DSL50 45 mV TSL 601&602 80 mV
DSL100 90 mV DSL 401 1.375V
TSL100/122 90mV DSL201 .675V

 

[CharFace]

Hope this can help:

Video of biasing a DSL:

http://www.eurotubes.com/euro-Marshall-DSLTSLV.htm

Here's the Marshall Service Bulletin on biasing the JCM2000 series amps:

Procedure:
1. Make sure the amp is connected to a load with the proper impedance selected.
2. Power up amp on Standby, and let the circuit stabilize for a couple of minutes.
3. Locate the male three pin molex connector (CON2) with the two mini pots (PR1 and PR2) (located on each side of the molex connector) on both ends found at the bottom of tube bay.
4. Connect DMM (set to read mV) with alligator leads, reference common lead to center pin (pin2) on molex connector CON2 and positive lead to pin1 on CON2.
5. Take amp off Standby with no signal, adjust mini-pot (PR1) closest to pin that the positive lead from your DMM is connected to and set it to mV voltage that is listed below.
6. Repeat steps 4 & 5 for pin3 mV and until pin1 & pin3 mV readings are the same.

Bias Settings:
DSL50 45 mV TSL 601&602 80 mV
DSL100 90 mV DSL 401 1.375V
TSL100/122 90mV DSL201 .675V

Beat me to it

I used the info from this video to bias my DSL100, but I don't remember neither the video nor the webpage making any mention of the DSL401

 

[BenoA]

Beat me to it

I used the info from this video to bias my DSL100, but I don't remember neither the video nor the webpage making any mention of the DSL401

You are right, the video is for a amp head, not a combo but I bet the method is quite similar...