Dsl100hr External Bias Point Question

[sjruvolo]

Opened up my DSL 100HR. Checked the bias reading. My multi-meter (set to DC and mv) read about -70 mv on each side.

 

[K2JLX]

Opened up my DSL 100HR. Checked the bias reading. My multi-meter (set to DC and mv) read about -70 mv on each side.

What were your plate volts (pin 3)?

 

[Michael Inglis]

Opened up my DSL 100HR. Checked the bias reading. My multi-meter (set to DC and mv) read about -70 mv on each side.

I'll write more later but I had to come here to say that having my bias at 80mv has made this amp sound 100x better. I imagine they ship them on the cold side cause it's less likely to have an issue arise(plus colder tubes tend to last longer as long as they are within reasonable range). But there is no doubt in my mind that having the bias set at 80 per side has cleaned up and compressed my gain (compressed in a good way). I was worried about it effecting my clean channel and it has but also for the better. My clean channel and crunch channel have greatly improved sounding fuller and more powerful even at lower volumes. I don't think I'll even need the OD2 channel anymore. The OD1 channel sounds great and if I want more gain or clarity I boost it with a tube screamer and it gets even better. Before a tube screamer wouldn't really help cause it was such a huge tonal gap between the amp gain tone and the ts9 tone. That is not a problem now. I'm easily getting that classic marshall tone and that classic TS9 boost "chirp" in the low end. It was in my head this whole time that I might like a hotter bias but I never expected the amp to perform this much better. I wished id tried it sooner. Maybe there is something to the 90mv service bulletin. I could only bias as high as 80mv on the right 2 power tubes. The left 2 would reach up to 87 but maxed out. And obviously since they need to be matched that's how I ended up on 80mv.

 

[sjruvolo]

What were your plate volts (pin 3)?

Didn't take a reading of the plate voltage. Just checked the bias by the external bias points.

 

[Michael Inglis]

I'd be very interested to know the plate volts aswell so we know where this amp really should be. 73 might actually be where it is ideal cause then the od2 fits more in your gain range but it sounds so much better at 80mv using just your other three channels in my opinion. I might still use it as a lead channel every now and then. But I'd almost rather buy a dedicated boost pedal for leads. Od2 does not sound bad at this bias but it just becomes unessesary. If I wasn't using a TS9 then I would probably use it. Anyways it's only been a couple days so I'll post back after awhile. I just want to really drive in the 80mv recommendation. These amps seem to be coming from the factory biased cold and really arent living up to there full potential. Id go a step further and say my amp didn't even sound as much like a marshall at first when the bias was 67. Even at 74 the gain was lacking definition. Just try it, if you don't like it you can very easily change it back.

 

[Michael Inglis]

Wow, once again I'm impressed. To my surprise OD2 actually sounds really good for a lower frequency/end high gain. I wasn't using the TS9 in front of OD2 before but now that I am it really tightens it up and gives me a great high gain tone. OD1 boosted is more mid rangey while boosted OD2 is bassier which could be better for lower volume an isolated guitar tracking. They would both sit in a mix well it just comes down to what the track needs. Rebiasing has really brought it to life. When I originally biased it I went off of the recommended logical setting which ended up being 74mv. It sounded much better since it came biased at 67mv. I didn't stop to think about how a high gain amp would probably sound better with the bias a bit above average. I have a pro co rat and a DS1 on my board aswell as the TS9 for my external dirt. They were from my old at home practise setup(orange lunchbox head) and they sound much better now aswell. Before they would sound wide open(very solid state mid range saturated) but now that the amp has a lower ceiling the pedal gain is interacting with the tube/amp natural gain which produces a much better tone. In other words all my pedals sound better now, go figure right? Hah! Who woulda thought your amp having a better tone would translate to your pedals having better tone?

 

[Michael Inglis]

Last thought, im sure this setup sounds much better for my rig because i dont crank the amp for gain. I have the 100watts so i can get enough clean(Crystal clear cleans very low gain) headroom to be heard over drums. But I don't ever have to really crank the amps gain volume to be heard. My point is that this is probably why a hotter bias works so much better for me. It helps my amp break up quicker but also since there's so much power on tap i still have plenty of clean headroom.

 

[sjruvolo]

My amp came from the factory at about 70mv. I now have the bias set at 72mv. I'm going to play it for a while, then I'm going to bump it to 75mv and give it some more time to see how it sounds. Thanks for the advise.

 

[Humanoid]

I believe in a few other threads the newer DSL40CR was mentioned with indications of 410-420VDC.

Here in this thread 406 and 426 was mentioned for plate voltage. 426 was with a 122VAC wall voltage.
http://www.marshallforum.com/threads/marshall-dsl40cr-bias.100693/

That would leave a 35mA or 37mA a little on the average side. Hotter would be more like in the 40's.

Measured plate voltage on my DSL100HR @ 439V with 123VAC at the wall. Bias set to 76mV.

 

[Dmann]

remember, the recommended setting is only a starting point, a factory default, if you will. The JVM I owned liked EL34 winged C tubes at 34.5 each or 69 mV a side, where with Ruby EL34 BSTR's it was 41 each or 82 mV a side. JJ 6CA7's liked it cold, 30 each or 60 mV per side.

what I learned going through all this years ago and what have done since was, forget about getting plate voltage and blah blah blah, just set it to 70 mV after warming it up for 20 min and then check it by ear and go with what "SOUNDS" the best, then take note of the readings because in my experience dialing stuff in with your eyes never works out to sound the best..... so I start at 70, then put it to 75, then down to 65. take a mic recording of each setting so you can easily compare.

YYMV, enjoy the chase.

 

[Martin Adams]

After speaking with Marshall UK I have set my DSL100 HR as 70mv per side and it sounds great. 70mv is the factory setting and not 90mv as per the older DSL100/ JCM 2000 etc

 

[DonP]

I like to shoot for the low 70s with my 1998 DSL100. Might be why I haven't had the runaway bias issue yet (bought the amp new). I ran the original winged C's for 20 years and just put in some old school GT Teslas from the early 90s. Those tubes run hot. I had to turn the negative bias way up to get the tube current down to about 73mA per side.

 

[RunForCover]

My amp came from the factory at about 70mv. I now have the bias set at 72mv. I'm going to play it for a while, then I'm going to bump it to 75mv and give it some more time to see how it sounds. Thanks for the advise.

The Marshall factory setting is 70mV per side on the new DSL100HR unlike the older version that were 90mV !!

 

[RunForCover]

This is an old thread but I still remember. The bias was set low upon arrival, marshall recommends a bias of 73(Not 90 which is floating around for some reason) and mine came biased around 67-68. It didn't sound bad but I found 74 to be much better. I didn't go for 74 specifically it just was where I got it when aiming for 73 and it sounded good so I left it. The pots and bias points are awesome, no alligator clips needed.

Marshall recommend 70mV per side on the DSL100HR and the old DSL/JCM2000 were 90mV per side hence the confusion

 

[ampmadscientist]

Hope this makes sense.... Summary:
How do these bias points work, why are there two trim pots?

I just got a new DSL and found out to my elation that it has external bias points on top of the chassi. My question is about the trim pots. It's probably obvious but there are the standard three points left red hot, middle black ground, and right red hot. Below these are two trim pots, are these for two power tubes each respective to the side they are on(as in biasing two tubes at once) or is it for the left side/right side depending on where your lead is(as in if your lead is on the left and you dial the left trim pot then your biasing power tube 1, and if you dial the right trim pot your biasing PT2? Then the same for PT3 an PT4 but with the hot lead on the right?). I have sone very limited experience with a single pot for two tubes but that is self explanatory this is a little more confusing and I can't find anything explaining it yet. The amp sounds great and I'd like to take note of where it's at for whenever the time comes to change the power tubes and reset the bias. Thanks to anyone who can explain or point me in the right direction.

The design causes you to measure plate current + screen current added together.
This is why it's not accurate.
You would be better off using a bias probe that is set up for plate current only.

Using the "formula," the plate current looks like it's much more that it really is. This is why using the formula is not even accurate.

If you set it and it drifts: the bias pot is probably bad. This is another problem, cheap unreliable pots.

New design / updated amp....but several of the bugs were not addressed in the new design. Too bad, because they could have fixed the bugs (and should have).

Cold Setting: from the factory, of course. They don't need any tube failures when the warrantee is still valid. Most factories do set the bias cold on purpose....this makes everything last longer (but it doesn't sound as good cold).

 

[charveldan]

Bias is set in relation to plate voltage.
If you dont know your PV you're not going to get the correct bias.
But if you have no experience with amps i wouldn't be poking around on hot tube sockets lest you have a shocking experience.

 

[Michael Inglis]

I've had this amp since launch and I've gotten so much more out of it then i ever expected. All my current guitars have high output humbuckers jb/59 set (not so much the 59) and my 7 string has fishman fluence modern 7's. So to get the amp working best with the pickups I rolled the tubes and found that the amp sounds best for me with lower gain 12ax7s. Eventually I'll try some 12at7s which could be even better. I'm using cv4004 mullards and a low gain JJ ecc83 in v1. My phase inverter is just a stock Chinese 12ax7b Shuguang but not for a lack of better tubes it just sounds the best cause it's lower gain then the other high gain 12ax7s I have. The lower the pre amp gain the better ive liked the tone so I'll keep trying new tubes. But for now it sounds great. I'm also using EH-EL34 power tubes now cause they arent as full sounding as the stock or after market jj's I tried. The Electro Harmonix EL34's are certainly an improvement but I want to try some el34 variants next along with a 12at7 in v1. Lots of guys swear by the kt77's in their 100h's so that's probably where I'll start. Also I still have my bias set to 80mv a side but if I was to go back to the stock JJ'S I'd have it down about 74mv. I said before I liked the stock tubes at 80mv but I believe that was because the v5 PT had started to fail. At first It sounded great at 74mv but then I noticed it started sounding really cold. So I went up to 80mv and it sounded better again but then a week or so later the v5 tube was gone. So compensating by turning up the bias exacerbated the problem with v5 and killed it a little quicker. But with the EH tubes they really do sound better at 80mv. I obviously want to keep my bias as low as possible to extend tube life so that might change. Im still trying different things but in the meantime I'm loving the amp. I can get several great tones at least from each channel now and use them all regularly. Since I changed the tubes to fit my setup I've been using my dirt pedals less and less except overdrive of course. I'm still using my ts9 but I've got a DIY klon centaur clone kit on the way and once I build it I'll have to make room for it next to my ts9. I'm currently running 10 pedals smh, I don't need more but I sure as hell want more. I just thought I'd update where I'm at with the amp. Its still surprising me with the tones im getting, as long as it never has a catastrophic failure I'll be keeping it indefinently. I'm running two 1x12 orange cabs with the marshall which sounds really really good to my ears. The head is on an amp stand with my pedals below it and in each side of the head is a cab.

 

[Hummarstra]

Hey guys, I'm trying to bias some tubes right now, but getting different reading in pentode an triode mode. Should I bias in pentode? 100h

 

[Micky]

Hey guys, I'm trying to bias some tubes right now, but getting different reading in pentode an triode mode. Should I bias in pentode? 100h

Yes, most definitely in pentode (full power) mode.

 

[Hummarstra]

Yes, most definitely in pentode (full power) mode.

Awesome. Thanks for the help.