Biasing a DSL40C

Discussion in 'The Workbench' started by ToneWarrior, Aug 2, 2014.

  1. ToneWarrior

    ToneWarrior Active Member

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    I wanted to check the bias on my DSL40C and I found it was set at 30mA the one side was running a little bit hotter at about 32mA. The tubes in it are a big bottle looking tube which I think I have identified as EL34B they are Marshall logo VLVE00092. So anyway doing research when I biased my JCM2000 DSL50 I found that EL34's should be biased between 35 and 40mA I found that I like the amp biased to 35mA because it sounds a lot cleaner and less fizzy. So that made me want to check the bias on the DSL40C which I've already described above. So going by what I did with the DSL50 I set the bias to 35mA and it wasn't as clear as I wanted it so I went down to 30mA which is where it was when I first checked it. It still wasn't what I wanted so I went down to 25mA and it cleaned up a lot but I was curious and I went further and set it at 20mA. I think this is the sweet spot for me but is it bad to run the amp this far down? Assuming the tubes I have are the same as a regular EL34 it's been recommended that they be set between 35 and 40mA but I do not like the way the amp sounds at those settings. I'm probably going to do the EVH thing anyway and run the amp the way my ears like it but I'm curious what could happen if the amp is biased so cold. Although it may be within the recommended mA's for these kind of tubes and that's why they sound good at 20mA. :shrug:
     
  2. mickeydg5

    mickeydg5 Well-Known Member

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  3. ToneWarrior

    ToneWarrior Active Member

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    Thanks, that thread has some good information but has grown into a monster that is hard to navigate and find the answer your looking for. I did a search on this site to find the answer but it didn't yield the results I was looking for. I should change the title of the thread because the question is more about biasing in general and not so much about the DSL40C - it just happens to be the amp in question.

    I did some research before starting this thread and didn't find the answer I was looking for. People like to give very technical answers which goes right over my head when I'm really just looking for a yes or no answer with a quick easy to understand explanation. This morning I did some more research but change the search words and I found this and it gave me the answer I was looking for which is pretty much what my insticts told me anyway but I like to ask anyway.
     
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  4. Micky

    Micky Well-Known Member VIP Member

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    Actually I found the tone lizard page confusing and contradictory.
    The DSL40c Info Thread has the bias info with photos right on the 1st page.
    Not hard to find at all.
    And 20 is very cold, but I cannot see what harm can come from it, other than tone that is lacking bass and mids. Plenty of clean headroom though...

    I ran mine at 39 for a while, but I needed more clean, not early breakup. So I backed it off to 35 or 36 and I am very happy. So are my final output tubes (TAD STR EL34b). Of course your mileage may vary. A 10% change for me gave me what I needed. With your settings you are talking about a 40-50% difference from factory...
     
  5. ToneWarrior

    ToneWarrior Active Member

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    All that tech mumbojumbo goes right over my head. I understand the point he's trying to make and as someone looking for simplicity in how to do something I took this quote from that "Gerald Weber states... 'any number (between 10mA and 40mA) that gives you the tone you like is correct." and satisfied my search.

    Yes but that's not the answer I was looking for. I was asking if running the amp cold would cause damage to the amp. The recommended mA's is irrelevant to me because I prefer the amp at a much lower setting.

    To me the amp sounds a lot more musical. The notes are a lot more defined and the fizzyness is gone. That's the one knock I have on all new amps. Granted I'm asking a lot of a new amp to sound like an old one but that's what I want. I like what new amps sound like but there's always something missing or I should say something added regardless of what new amp it is. When I pluck a string I want that note to come through as natural as possible and my theory is this. Old amps tube sections are setup to work together to give you your tone so the more you crank the amp the better it sounds. New amps rely on the preamp section for your tone and the power section to amplify the sound but add for me an unwanted amount of distortion and that's why they sound fizzy and un-natural. It's distortion on top of distortion and if you add a pedal it's distortion (pedal) on top of distortion (preamp) on top of distortion (power tubes) = a big fizzy un-natural sound. By running the amp cold I believe I've eliminate the power tubes from adding distortion to the overall tone and the preamp breakup is less affected and sounds a lot less fizzy and a lot more natural.

    I'm sure that there are variables that I haven't thought of but that's what I hear and that's the best I can describe it.

    I think clean is where it's at. I think it allows all the elements of the signal from your fingers to the speaker to come through and add all their specific effects on the overall tone without the amp being a big spike in the overall tone. If I could write out what I think new amps do to your tone it would look something like this. fingers>>>pickups>>>cables>>>AMPLIFIER>>>speaker. but I much prefer fingers>>>pickups>>>cables>>>AMPLIFIER>>>speaker.
     
  6. Micky

    Micky Well-Known Member VIP Member

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    If a Marshall is too distorted, then maybe you have the wrong amp.
    Certainly a DSL can sound clean, to a degree, but 9 out of 10 people did not buy it for that.
    Maybe a Fender might be more suited to your taste.

    But I totally understand what you are asking, and I don't think it is a question that is asked much. The bias current is much like the engine idle, a starting point for the way something runs. Like I said, too cold a bias will not harm an amp to my knowledge, but I DO know it will generally not sound like it was designed.

    It will not be as loud, and it will not have the gain it was designed to have. But if YOU like it, that is all that matters. I don't see any harm.
     
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  7. mickeydg5

    mickeydg5 Well-Known Member

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    There is nothing wrong with dropping the idle bias of the power tubes.
    It will definitely lower the output power and affect the frequency response dropping a good bit of highs which may be ok with this amplifier since so many have mentioned the heavy treble especially on the ULTRA channels but also diminishing other frequencies.

    10mA is very low though and the only concern would be crossover distortion. That does not sound good either.
     
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  8. ToneWarrior

    ToneWarrior Active Member

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    Cool thanks that's what I am looking for. But to clarify Marshall is not too distorted for me it's just all the new amps I've tried have a certain amount of fizz that I don't like and I've tried a lot up to and including the JVMHJS. A Plexi is a clean signal until you turn it up and push the tubes into saturation but it is designed for the tube sections to work together and give you a more natural distortion without the fizz. New amps are designed more for the bedroom player to get more distortion at lower levels but the down side is (for me anyway) it's a sacrifice of or a direction away from the Plexi type way people used to get their tone - which most of us want to achieve.

    I want distortion but I want it in the form of tube saturation but I need it in a more modern design of an amp with FX loop and channel switching. I could never get a comfortable tone with new amps - they don't sound natural to me until now. I can't wait to go to practice and put the amp to the test. I'm not going to say anything to anyone and see if anyone makes any comments about the amp good or bad.
     
  9. ToneWarrior

    ToneWarrior Active Member

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    I've read about the crossover distortion but I haven't experienced any yet. The real test will come when I go to practice and really push the amp.
     
  10. Bownse

    Bownse Well-Known Member

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    Just did my first bias. When bought used, I took it to a shop and had them do it for me. The readings (all JJ power tubes and Marshall AX7 preamp tubes) it was around 41.

    Decided to not dick around with probes and went straight to the Eurotube "Pro One" Bias Probe.

    That was about the cost of 2 shop biases. With auto and motorcycle tools that's about the sweet spot for justifying the purchase of a specialty tool (how long to recoup the cost).

    Swapped in 2 TAD EL34B-STR power tubes Antique Electronic Supply. The matched pair were marked B47 and B36 so I'm not quite sure how "matched" that is.

    Based on some recommendations (and what preamp tubes I had on hand), I also swapped in the following:

    V1-Tung-Sol 12AX7 (new)
    V2-Mullard RI 12AX7 (new)
    V3-Tung-Sol 12AX7 (new)
    V4-Marshall 12AX7 from V3 prior

    I have some TAD 7025WA on order as well as another Mullard on hand to roll once I try this for a while.

    ---

    I got the TAD one dialed in at around 35 (with n 20 minute warm up) and two around 34.5. Letting two run up for more than 30 minutes, I noticed some creep up to near 36. I continued to let it run for a while to see where it settled down at then went back to one and dialed it in to 36 as well.

    I know creep is normal but I also saw that there is may be an issue with some Viet Nam builds where the creep is outside of acceptable.

    This is new territory for me so feedback is welcome.
     
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  11. Jethro Rocker

    Jethro Rocker Well-Known Member Silver Supporting Member

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    That sounds perfect to me, I also have the Eurotubes probe. Works great!! I set my 6101 slightly lower as it seems to sound better to me but note to Tone Warrior - when I bought it used, it sounded flubby on bass notes and just not right. Bias was 12mV!! Starved for power at that rate. Before I checked that, I changed the power tubes out to a set from another amp. As soon as I turned it on, HT fuse blew. Seems like that set of tubes, whatever the bias should be, couldn't run on that low a voltage. Put the old ones back and rebiased. I now have new ones in BTW.
     
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  12. Bownse

    Bownse Well-Known Member

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    --Update--

    (first posted in the wrong thread. it's still okay there, but it's more accurately a follow up to my above post.)

    Based on some PMs I first set things up as show above:

    Matched pair of T-EL34B-TAD-MP
    V1 to V4
    TungSol T-12AX7-TUNG
    Mullard (Russian) T-12AX7-MUL
    TungSol T-12AX7-TUNG
    OEM Marshall (JJ?) 12AX7
    Also put damper rings on all tubes. End result is that it sounded "more melodic".


    Ran those about a month.

    Just swapped V1 for a TAD 7025WA HG. With the first chord I could tell it was warmer. Nothing detrimental to the previous improvements.
     
  13. Bownse

    Bownse Well-Known Member

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    This isn't a Marshall but it's the best example I've seen of the voltages inside a tube amp.

    Over and over again everyone warns everyone else about the risks of working inside your amp. Here's one reason why.

    http://youtu.be/Az9poDQN6ag
     
  14. Speegman

    Speegman Member

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    I want to swap out preamp tubes on DSL40C - does this require bias? Thanks!
     
  15. Micky

    Micky Well-Known Member VIP Member

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    No
     
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  16. Speegman

    Speegman Member

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    Thanks!
     
  17. Demo Danner

    Demo Danner New Member

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    I had to change the speaker in mine to warm it up, (V-type 75 watt Celestion. Then I built a closed back ext. cab. out of the 70/80 I pulled out of it. It was played in for just over a year.) that and a bias setting along with a set of matched Mullard power tubes. No C-19 mod, it sounds great without that. The cleans on mine are pristine! If you want to add some warmth and depth to this amp, try adding an ext. cab., it really brings out the best of the DSL 40C! If your gonna use the 70/80, then definitely go with a closed back cab., then it will push the bass frequencies out the front instead of being lost out the rear of the cab. Good luck, and Cheers!
     
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  18. Bownse

    Bownse Well-Known Member

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