DSLs ..run em' cool..

[SWM510]

Adrian you and I are on the same page when it comes to this, biasing them colder that Marshall recommends allows them to run cooler and we both agree that they sound much better.

And in the end what truly matters is having an amp that has the TONE (as long as no one does any damage to their amp trying to get that tone.....hehe...)

 

[Rahlstin]

If I ran my 100w at 38 / side or 19 per tube im only producing like
9 watts per tube. My DSL puts out 465 on the plate and according to the bias chart its should be at 38.7/tube, not per pair. (77.4 per side which sounds pretty dull) If im running at over 100% too high, id expect alot of cherry going nuclear tubes melting the guts out of themselves, but never had this since new in 2005. Also, my amp came from Marshall at 93ma/ side of the connector and I backed that down at the time as i thought that was nuts. Each to thier own. My JVM410H came at 58 per side from Marshall but i run it a bit higher. SMW510's explanation is likely what the confusion is about.

 

[codyjarrett]

Runnin these DSL's cold like this will introduce crossover distortion ,which personally I don't like.

 

[SWM510]

The more I read this thread the more confused I'm getting.....lol...

I was reading a thread about biasing the DSL's on another forum and I think we're all basically correct, it's just the way we are explaining things is what is making it confusing.

My DSL 100 has a plate voltage of 477mA and I wanted to bias it at 65% dissipation so, EL 34's are 25 watts so I divided 25 by 477 which equals .0524 multiplied that by 1000 which equals 52.4 and multiplied that by 65% equals 34.06 multiply that by 2 (2 tubes per side) equals 68.12
This is what I biased it at, now when I use the bias probe it shows 34.06 per side (only showing a reading for one tube) but when I just use the DMM it shows 68.12 per side (showing a reading for both tubes)

I think when some of us are saying we biased it at 30 something per side when we used a bias probe, we just didn't explain that we multiplied that number by two (two tubes per side) and for those of you that just use a DMM to bias then that number sounds far too low but in actuality we've just forgot to mention that number is multiplied by two which would put the bias in the 60's - 70's mA range.

Hopefully this doesn't cause any further confusion and makes some kind of sense

And hopefully one of the tech's can properly explain this so no one gets confused and will correct me if I've biased my amp wrong

 

[RiverRatt]

Of course the value that marshall gives per side for the 50/100 watt may also include the 5ma that the screen current or it may not so 45/90 respectivley may not be as hot as we imagine.

Yes, it's been proven that it does include the screen current, so subtract 4 or 5 (or 8 to 10) mA from your reading to figure out what you're actually running at. I think 45 is too high as well, but it really depends on the amp and the pair or quad of tubes you're using. The Winged C's I had actually liked it closer to 42-44mV per tube and the RFT EL34's were happy running at 41mV per side. GT EL34M's were the only ones that sounded good cold in my amp - around 36 to 38mV. I do things ass backwards. I bias my tubes for tone with one eye on the DMM's to make sure I'm not going too hot or too cold. When they sound the best within my operating range, that's where I stop. There is no one bias number that will work for all tubes and all amps. It doesn't work that way.

 

[diesect20022000]

Yes, it's been proven that it does include the screen current, so subtract 4 or 5 (or 8 to 10) mA from your reading to figure out what you're actually running at. I think 45 is too high as well, but it really depends on the amp and the pair or quad of tubes you're using. The Winged C's I had actually liked it closer to 42-44mV per tube and the RFT EL34's were happy running at 41mV per side. GT EL34M's were the only ones that sounded good cold in my amp - around 36 to 38mV. I do things ass backwards. I bias my tubes for tone with one eye on the DMM's to make sure I'm not going too hot or too cold. When they sound the best within my operating range, that's where I stop. There is no one bias number that will work for all tubes and all amps. It doesn't work that way.

that's a good point. i was using JJ E34L's at 42ma per side but i'd gotten into 40ma per side and that seemed about right in most cases but i also only went through 1-2 pairs per DSL100 i owned. to get the same tone some were 40 and some were 42 but pretty close in range.

the EH's i had just sounded bad in the DSL. they sounded best at 38ma per side to me but still a little rough.

 

[el zilcho]

Always do whatever it takes to get the sound you want. But, FYI:

 

[poeman33]

I think it's been explained before in a thread years ago...but the search on here is so-so sometimes when you want to find something specific...

Is there a difference in value between mV and mA ? Marshall shows the values for mV and that is how my DMM reads it...so I have always set my DSL50 close to 45mV. Would the values you guys are talking about for mA be different...and that is why they are so much lower?

 

[codyjarrett]

Not the same but when taking a bias current measurement, you measure it as voltage across a 1 ohm resistor...hence 1mA becomes 1 mV.

 

[Bieling3]

All I know is that when I had my TSL100 the hotter I ran it the better it sounded. If I ran it cold, around the levels recommended in the op, the amp sounded cold, sterile, and gritty. Biased hot it sounded warm, full, and smooth. Just my observations. YMMV.

 

[truckdub]

Always do whatever it takes to get the sound you want. But, FYI:

Using this method I set my DSL 50 cool at around 38mv and it sounds great!

 

[RiverRatt]

that's a good point. i was using JJ E34L's at 42ma per side but i'd gotten into 40ma per side and that seemed about right in most cases but i also only went through 1-2 pairs per DSL100 i owned. to get the same tone some were 40 and some were 42 but pretty close in range.

the EH's i had just sounded bad in the DSL. they sounded best at 38ma per side to me but still a little rough.

Die, those EH tubes are a direct descendant of the Sovtek EL34G, probably the worst EL34 to come out of Russia.

Yeah, I hear what you're saying. I usually stayed within a 5mV range, too.

 

[RickyLee]

Always do whatever it takes to get the sound you want. But, FYI:

Now let me give a shot at clearing up this debate about Marshall giving out these specs/instructions that end up with an end result of a DSL 50/100 & TSL100/122 that has a hot biased set of power tubes/valves.



I am wondering if Marshall used a MAINS Service voltage calculation for the 120VAC owners of the older seen MAINS of 115VAC? That would make more sense on having those 45mV/mA PER TUBE instructions. Now my home has a MAINS of 122VAC to 125VAC which puts my plate voltage at aprox. 480V.

Having my MAINS supplying 115VAC to 120VAC would put my plate voltage at the 450V to 460V range.

Now let's say my plate voltage was at 450V. And I want to go with the 65% power dissipation.

EL34 is 25W, 25W X 65% = 16.25W/450V = 36mA PER TUBE.

Add in 5mA of screen current PER TUBE to be conservative + 36mA = 41mA.

Now that is still under/colder from that Marshall spec up above. So let's figure going with a 70% power dissipation with the same 450V on the plates.

EL34 is 25W, 25W X 70% = 17.50W/450V = 39mA PER TUBE.

Add in 5mA of screen current PER TUBE to be conservative + 39mA = 44mA.

This is now starting to make some sense coming from an amp designed in the U.K. and then I would think that the MAINS over there might show an amp with a lower plate voltage than what the 120VAC MAINS users see (I would like to here some of the MAINS measured from some of you guys on the Other Side Of The Pond).

I am thinking that Marshall might still be figuring in with the 115VAC to 120VAC calculations. But I have heard of many people getting 125VAC as I have seen mine here go up to almost 126VAC.

Keep in mind that some of the Old Timers might still be calculating out 110VAC MAINS.



EDIT: As in the DSL50/100 & TSL100/122 amps with their bias test points AND if you are using the bias probe adapter sockets, you are measuring across a 1 Ohm resistor between pin 8,1 and Common/Ground/Negative. So you are seeing the Screen current as well. This screen current varies a bit. Using the 5mA is conservative and a good Rule Of Thumb. And as mentioned before, you are seeing mV which translates into = mA from Ohm's Law.

 

[Adrian R]

Now let me give a shot at clearing up this debate about Marshall giving out these specs/instructions that end up with an end result of a DSL 50/100 & TSL100/122 that has a hot biased set of power tubes/valves.



I am wondering if Marshall used a MAINS Service voltage calculation for the 120VAC owners of the older seen MAINS of 115VAC? That would make more sense on having those 45mV/mA PER TUBE instructions. Now my home has a MAINS of 122VAC to 125VAC which puts my plate voltage at aprox. 480V.

Having my MAINS supplying 115VAC to 120VAC would put my plate voltage at the 450V to 460V range.

Now let's say my plate voltage was at 450V. And I want to go with the 65% power dissipation.

EL34 is 25W, 25W X 65% = 16.25W/450V = 36mA PER TUBE.

Add in 5mA of screen current PER TUBE to be conservative + 36mA = 41mA.

Now that is still under/colder from that Marshall spec up above. So let's figure going with a 70% power dissipation with the same 450V on the plates.

EL34 is 25W, 25W X 70% = 17.50W/450V = 39mA PER TUBE.

Add in 5mA of screen current PER TUBE to be conservative + 39mA = 44mA.

This is now starting to make some sense coming from an amp designed in the U.K. and then I would think that the MAINS over there might show an amp with a lower plate voltage than what the 120VAC MAINS users see (I would like to here some of the MAINS measured from some of you guys on the Other Side Of The Pond).

I am thinking that Marshall might still be figuring in with the 115VAC to 120VAC calculations. But I have heard of many people getting 125VAC as I have seen mine here go up to almost 126VAC.

Keep in mind that some of the Old Timers might still be calculating out 110VAC MAINS.



EDIT: As in the DSL50/100 & TSL100/122 amps with their bias test points AND if you are using the bias probe adapter sockets, you are measuring across a 1 Ohm resistor between pin 8,1 and Common/Ground/Negative. So you are seeing the Screen current as well. This screen current varies a bit. Using the 5mA is conservative and a good Rule Of Thumb. And as mentioned before, you are seeing mV which translates into = mA from Ohm's Law.

Interesting, never thought to much about varying power sources...but I see how that would have a direct affect on the amp's plate voltage..

Either way, this debate is pretty much concluded with the Marshall spec bulletin as illustrated. 90mV across pin one AND three...to me this still means 45mV PER SIDE....DSL50 specs as shown above are again divided by TWO..that is what I get out of that spec. I like running colder...36-38mA....the amp sounds better and stays relatively cool...it just makes good sense to me to try and run as cool as possible..while still maintaining good tone...this involves some trials...

And in the end I still cannot forget all of the 100w Marshalls I have owned in the past...they ALL had similar plate voltages and all biased within the same parameters....(30-42mA). The older Marshalls had only one bias control pot...

 

[SpiritOfTheAge]

Now let me give a shot at clearing up this debate about Marshall giving out these specs/instructions that end up with an end result of a DSL 50/100 & TSL100/122 that has a hot biased set of power tubes/valves.



I am wondering if Marshall used a MAINS Service voltage calculation for the 120VAC owners of the older seen MAINS of 115VAC? That would make more sense on having those 45mV/mA PER TUBE instructions. Now my home has a MAINS of 122VAC to 125VAC which puts my plate voltage at aprox. 480V.

Having my MAINS supplying 115VAC to 120VAC would put my plate voltage at the 450V to 460V range.

Now let's say my plate voltage was at 450V. And I want to go with the 65% power dissipation.

EL34 is 25W, 25W X 65% = 16.25W/450V = 36mA PER TUBE.

Add in 5mA of screen current PER TUBE to be conservative + 36mA = 41mA.

Now that is still under/colder from that Marshall spec up above. So let's figure going with a 70% power dissipation with the same 450V on the plates.

EL34 is 25W, 25W X 70% = 17.50W/450V = 39mA PER TUBE.

Add in 5mA of screen current PER TUBE to be conservative + 39mA = 44mA.

This is now starting to make some sense coming from an amp designed in the U.K. and then I would think that the MAINS over there might show an amp with a lower plate voltage than what the 120VAC MAINS users see (I would like to here some of the MAINS measured from some of you guys on the Other Side Of The Pond).

I am thinking that Marshall might still be figuring in with the 115VAC to 120VAC calculations. But I have heard of many people getting 125VAC as I have seen mine here go up to almost 126VAC.

Keep in mind that some of the Old Timers might still be calculating out 110VAC MAINS.



EDIT: As in the DSL50/100 & TSL100/122 amps with their bias test points AND if you are using the bias probe adapter sockets, you are measuring across a 1 Ohm resistor between pin 8,1 and Common/Ground/Negative. So you are seeing the Screen current as well. This screen current varies a bit. Using the 5mA is conservative and a good Rule Of Thumb. And as mentioned before, you are seeing mV which translates into = mA from Ohm's Law.

Ricky, I'm from the UK and my DSL 50s plate voltage is around 492 (same for the jcm 900 i have) with no valves in and around 488 with valves in.

I aim to bias at around 65% and allowing a few mA for screen current and using my ears to settle on a value, and If i reacall correctly its biased at 36mA (per side)using the points on the back of the head.

My jcm 900 sounds better around 33mA per valve though, I use a 4 probe bias tool for this so can see the mA for each valve as i bias.

DSL has winged C's in and the JCM 900 has RFT's

 

[SpiritOfTheAge]

Interesting, never thought to much about varying power sources...but I see how that would have a direct affect on the amp's plate voltage..

Either way, this debate is pretty much concluded with the Marshall spec bulletin as illustrated. 90mV across pin one AND three...to me this still means 45mV PER SIDE....DSL50 specs as shown above are again divided by TWO..that is what I get out of that spec. I like running colder...36-38mA....the amp sounds better and stays relatively cool...it just makes good sense to me to try and run as cool as possible..while still maintaining good tone...this involves some trials...

And in the end I still cannot forget all of the 100w Marshalls I have owned in the past...they ALL had similar plate voltages and all biased within the same parameters....(30-42mA). The older Marshalls had only one bias control pot...

Adrian for the love of god, it clearly states in step 5 that you measure the value in the pin 1 to ground and aim for 90mV on a DSL100 this is for 1 side.

Then step 6 is repeat this for pin 3 and again use the value in the table below for this side.

So each side is supposed to be around 90mV, not the total for both sides.

Listen, I'm trying to help you and anyone else reading this that is not sure what the value is supposed to be, you are wrong in your assumption that 90mV is the total value for both pins and by continually stating this potentially mislead people.

I'm not trying to get in your face with this, I really am just trying to help.

Sorry for the love of god opening remark but really dude, come on.

 

[Adrian R]

Adrian for the love of god, it clearly states in step 5 that you measure the value in the pin 1 to ground and aim for 90mV on a DSL100 this is for 1 side.

Then step 6 is repeat this for pin 3 and again use the value in the table below for this side.

So each side is supposed to be around 90mV, not the total for both sides.

Listen, I'm trying to help you and anyone else reading this that is not sure what the value is supposed to be, you are wrong in your assumption that 90mV is the total value for both pins and by continually stating this potentially mislead people.

I'm not trying to get in your face with this, I really am just trying to help.

Sorry for the love of god opening remark but really dude, come on.

I know man, I mean if you are using a bias probe you are only measuring the current in one tube only...I meant to state 'while using a bias probe' sorry my bad...

 

[RickyLee]

I think everybody here has a general grasp and basic understanding about this JCM2000 series biasing and the test point terminals. But something I just noticed on that Marshall spec chart has me quite baffled and alarmed as well.

For the TSL60/1/2 I am figuring they are talking about the TSL60, TSL601 & TSL602. These models are the 50W - 60W and run only TWO POWER TUBES TOTAL. They are giving a mV test point of 80mV. Can someone here tell me if the bias terminal test point on the back of these is measuring both sides of the output transformer push pull/both/all power tubes? Or is it the same as the DSL50/100 TSL100/122 and there's a dual trimmer pot and you are measuring each EL34/each side? I guess I can look at the schematic to check this as well.



@Adrian: I am still confused on where you are biasing your DSL100?

. . . DSL100: 38mA per SIDE...(two tubes)..my amps sound KICK ASS.... I'm done though..anyone who wants their DSLs to sound like proper Marshalls..that is tight, with great mids...warm with good, wall shaking power.. etc..do as I have done if not..then cool: enjoy the slop...

So are you going way into the cold side at 19mA EACH TUBE? Or is it actually 38mA EACH TUBE?

 

[Adrian R]

I think everybody here has a general grasp and basic understanding about this JCM2000 series biasing and the test point terminals. But something I just noticed on that Marshall spec chart has me quite baffled and alarmed as well.

For the TSL60/1/2 I am figuring they are talking about the TSL60, TSL601 & TSL602. These models are the 50W - 60W and run only TWO POWER TUBES TOTAL. They are giving a mV test point of 80mV. Can someone here tell me if the bias terminal test point on the back of these is measuring both sides of the output transformer push pull/both/all power tubes? Or is it the same as the DSL50/100 TSL100/122 and there's a dual trimmer pot and you are measuring each EL34/each side? I guess I can look at the schematic to check this as well.



@Adrian: I am still confused on where you are biasing your DSL100?


So are you going way into the cold side at 19mA EACH TUBE? Or is it actually 38mA EACH TUBE?

Using a bias probe...I am only measuring the current of one tube..I set this for 36-38mA...I can only assume that the bias trim pot adjusts for both tube sockets evenly. Therefore the total bias of BOTH SIDES would be 38 x 2....

 

[TwinACStacks]

I biased my DSL100 @ 77.1 per side which was the sweet spot for this amp. This includes the allowance for 10MV/ side for the screens.

TWIN