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jegler

DT25 Voicing&Class settings for LongTubeLife

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DT25 Voicing&Class settings for LongTubeLife


 


Can anyone tell me if the voicing and/or class settings on the DT25 are any harder or easier on the tube life of the amp? That is: if I had every patch play Class A/B Pentode, would that shorten tube life compared to Class A Triode? or viseversa?


 


Does switching back and forth voice/class settings stress the amp or tubes? 


 


After getting my amp back from service, my tubes were factory replaced and re-biased, sounded glorious, but tubes are wearing out after <100 hours. I set all patches to Class A/B Pentode and tubes are EH


 


I bought a stash of EH replacement pre's and power tubes. I can just plunk those in and expect to be up and running. Right?

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We're supposed to wait at least 5 seconds after a switch before switching again.  If you switch faster than that, it probably wouldn't do you any good.  If you plunk in the exact EH tubes, you'll still need to get the power tubes (must be matched pair) biased.  I'd bet Class A/Triode and Voice III would burn up your tubes the fastest, but wait until the Line 6 gurus weigh in for a better answer than mine.  

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A always wears tubes faster than AB...if you are running ab mode loud then it doesn't make any difference. 

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Line6 support told me that it was quite ok to switch through the preamp models at will. Although they've been full of it more often than not. Where did this 5 second suggestion come from?

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Line6 support told me that it was quite ok to switch through the preamp models at will. Although they've been full of it more often than not. Where did this 5 second suggestion come from?

one of those downloadable manuals,  the quickie pilots guide or something like that.

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I'll be real careful with my next pair of jj's and see if they last longer.

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 If you plunk in the exact EH tubes, you'll still need to get the power tubes (must be matched pair) biased.

I so totally don't want to have to bias my tubes every time they wear out. (I don't have any qualified tech's close by, and the DT25 looks like a major pain to dissemble not to mention the money involved in either case.) Surely it's not that bad to go forth with tubes that are a bit out of whack, yeah? What's the worst that can happen? Seriously, what is the worst that can happen? I understand that even buying matched tubes (as I do) is still a crap shoot as to their tolerances. But big deal, right? Right? I'm kinda freakin out here... There has to be many many users who've plopped in mail-order tubes their whole lives. Or am I the only one? HaaHa, I've done it for years with my old 80's Fender Bassman and never had an issue, but the DT scares the lollipop outta me.

 

Thanks for all the great info everyone.

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Here's an idea...

 

Pay a tech to mod your amp...Get test points mounted on the back with a bias pot...Then you can bias your own amp safely...It's literally about $5 worth in parts to do it...One hour of labor is all a mod like that costs...It's a common mod...Then you can change tubes all you like safely and keep your bias in check any time you feel like it...

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I so totally don't want to have to bias my tubes every time they wear out. (I don't have any qualified tech's close by, and the DT25 looks like a major pain to dissemble not to mention the money involved in either case.) Surely it's not that bad to go forth with tubes that are a bit out of whack, yeah? What's the worst that can happen? Seriously, what is the worst that can happen? I understand that even buying matched tubes (as I do) is still a crap shoot as to their tolerances. But big deal, right? Right? I'm kinda freakin out here... There has to be many many users who've plopped in mail-order tubes their whole lives. Or am I the only one? HaaHa, I've done it for years with my old 80's Fender Bassman and never had an issue, but the DT scares the lollipop outta me.

 

Thanks for all the great info everyone.

 

As you already know, an 80's Fender is NOT a Bogner/Line 6 hybrid.

 

Sorry you're freaking out!  These amps are VERY particular about their tubes.  It actually freaks me out a bit too, but the tone is amazing so ya gotta deal with it.  Sticking with EH matched pairs is safest, but I don't know about not checking the bias. I don't know if you can just swap in a pair of EH tubes and get away with it, but my guess is that you might be taking a chance.  You could very well be right, but what if you're not?  Unlike Fenders and other clean amps, these amps get their mojo from the tubes' non-linear regions.

 

I hope someone who has actual knowledge of what effects there would be throughout the tolerance range of EH matched pairs in the DT can weigh in here and explain it to us definitively.  

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Did you know that EH, JJ, Tungsol, Mullard, Sovteks and other brands are actually branded and re-sold by a company called New Sensor (they own the brands)....Most all New Sensor brands of new Russian tubes are made in the Reflektor factory...I would tend to believe that EH is the better matched pair/quad brand out of the New Sensor brands for power tubes...New Sensor pretty much owns the tube market now...and the Reflektor factory...

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I'd heard all Russian tubes were made at the same factory, but didn't have the other details.  You have to wonder how much worldwide demand there is for tubes relative to demand prior to the rise of the transistor.  It can't be enough to justify a lot of competition between tube makers.  

 

With respect to Russia, I can't help but think that the consistency is so low that they actually attempt to make batches of the same tube, but wind up with vast differences between them.  So they get sorted and they get branded according to how they turn out.  As for China, same same only less quality (though they are improving).

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Here's an idea...

 

Pay a tech to mod your amp...Get test points mounted on the back with a bias pot...Then you can bias your own amp safely...It's literally about $5 worth in parts to do it...One hour of labor is all a mod like that costs...It's a common mod...Then you can change tubes all you like safely and keep your bias in check any time you feel like it...

This, of course, begs the question as to why Line6 doesn't do that anyway. The DT25's bias pot is mounted so that it is absolutely impossible to get to without entirely removing the chassis which, as I understand it, is screwed and glued in. Fk.

 

At any rate, does anyone have any experience with careless bias settings? I guess I already do - when my DT was shipped, it was suuuuuuper loud. I could barely use it for gigging. The tubes burnt out after about 25 hours of use. sent it back to the factory, when I received it: same deal. I sent it back again with an angry note demanding they triple check the bias of these tubes. Got it back and the amp sounded perfect and the tubes have lasted about 100 hours (they are just now giving hints of wear)

 

Anyway I second mtreehugers "I hope someone who has actual knowledge of what effects there would be throughout the tolerance range of EH matched pairs in the DT can weigh in here and explain it to us definitively. "

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A always wears tubes faster than AB...if you are running ab mode loud then it doesn't make any difference. 

I had been running all patches AB/pent, then I think in a post of yours I read  that if you have the DT running Class A all the time that the bias is irrelevant. You say it burns out the tubes faster, but if it saves the hassle of biasing everytime it'd kinda be worth it for a lazy sod like me, doncha think? Tubes are a constant money soak, but so is paying a tech, or buying measurement gear and the time you spend and....

 

as a guru/expert, could you give an estimate as to the wear ratio between A and A/B? like: A wears twice as fast, or 20 times as fast? or, hopefully, 1.1 times as fast.

 

I'm gonna switch a batch of patches to all class A and see if I like the sound, if so, would this be a harmless workaround of having to bias my power tubes at every swap? Would it put undue heat stress on the amp?

 

Do the pent/tri settings have any factor in the biasing/tube life?

 

I want to settle into a "routine" setup that ensures long life for my amp, with minimal screwdrivin on my part so I'm willing to try whatever. 

 

Ideally I could set all patches to class A, never touch the bias pot, buy an octet of matched el84's every year and just plunk 'em in a pair at a time. Please tell me that's an awesome idea. 

 

Thank you for your time, everyone.

 

JTV69>VDI>PODHD500>L6>DT25combo

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I had been running all patches AB/pent, then I think in a post of yours I read  that if you have the DT running Class A all the time that the bias is irrelevant. You say it burns out the tubes faster, but if it saves the hassle of biasing everytime it'd kinda be worth it for a lazy sod like me, doncha think? Tubes are a constant money soak, but so is paying a tech, or buying measurement gear and the time you spend and....

 

as a guru/expert, could you give an estimate as to the wear ratio between A and A/B? like: A wears twice as fast, or 20 times as fast? or, hopefully, 1.1 times as fast.

 

I'm gonna switch a batch of patches to all class A and see if I like the sound, if so, would this be a harmless workaround of having to bias my power tubes at every swap? Would it put undue heat stress on the amp?

 

Do the pent/tri settings have any factor in the biasing/tube life?

 

I want to settle into a "routine" setup that ensures long life for my amp, with minimal screwdrivin on my part so I'm willing to try whatever. 

 

Ideally I could set all patches to class A, never touch the bias pot, buy an octet of matched el84's every year and just plunk 'em in a pair at a time. Please tell me that's an awesome idea. 

 

Thank you for your time, everyone.

 

JTV69>VDI>PODHD500>L6>DT25combo

 

I've been wondering the same thing.  (Not sure I like the tone though--to my ears it doesn't seem to match Vox)

 

I'd also like to know more about "if you are running ab mode loud then it doesn't make any difference."  Does "loud" mean high gain?  So would tubes burn out sooner in Class AB pentode voice III than Class AB pentode voice I?  Or does "loud" mean master and channel volumes up high.  What about low power mode--is that better?  Finally, If I use POD HD simulated distortion pedals, that kind of "saturation" would be irrelevant to tube life, right?  

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Surely it's not that bad to go forth with tubes that are a bit out of whack, yeah? What's the worst that can happen? Seriously, what is the worst that can happen?

I used a matched pair of jj's bihsed to 25mv and they lasted 3 months of mild use before one melted. Second matched pair lasted about the same. So, being in a pinch, I used the surviving tube from the first and second pairs together, totally unmatched and out by 15mv if I remember correctly. These have lasted muoh longer. There is a deep low humming from the amp which is the only issue I've noticed. I've heard rumours that running unmatched tubes can magnetize your output transformer, but others have said that this doesn't matter and is nothing to worry about.

 

You probably want to get the bias sorted tho. You don't need to disassemble the amp; you remove the two woooen slats from the back (the combo I presume) and stick a multimeter into the measuring holes. Its a bit fiddly, and a torch and mirror can help you at first, but when you know what you're trying to hit it's easy. I took my head out of the combo the first time, to get a better look at it, now I just poke around by feel till I get the reading.

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Here's an idea...

 

Pay a tech to mod your amp...Get test points mounted on the back with a bias pot...Then you can bias your own amp safely...It's literally about $5 worth in parts to do it...One hour of labor is all a mod like that costs...It's a common mod...Then you can change tubes all you like safely and keep your bias in check any time you feel like it...

After gathering u as much info as I could, I'm resigned to go ahead and bias my tubes after very change. but there's no tech guy in my town and so I guess I'll do it myself. Is there a thread on the forums that covers this mod in more detail? I searched but couldn't find anything. Thanks for your time 

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BTW this is from tech support

 

1) Keep it correctly bias anyway. The power tubes still have to be correctly referenced. 1a) When swapping tubes, they still have to be correctly biased, so that the reference points are correct. Non-linearity can/will occur, and that leads to a host of distortion related problems.

2) Class-A can "... burns out the tubes faster",... yes, if you drive it harder. In general tube wear is about 12-18 months if you're a continually gigging musician (Class-A or A/B). Class-A runs a little hotter,... has to do the thermal dynamic physics (I won't get into that here) of running signal 360-degrees, as opposed to 180-degrees at a time.

3)"Do the pent/tri settings have any factor in the biasing/tube life? either in A or A/B?"--- No, the switches just engage a different gain loop into the signal path for whatever is called for by those switches. So bias must be maintained for optimum performance.

These are hybrid amps, DSP with vacuum tubes amp stage,... they are not designed to be modified.

These aren't our grandfather's tube amps like the old days (1950's, 60's and 70's). Use the specified matched set tube types (no JJ's, Mesa's or Groove Tubes, they don't bias the same, they go non-linear too soon).

Bias will have to be checked and adjusted whenever you change out the tubes (even if you get a matched octets and change two at a time).

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After gathering u as much info as I could, I'm resigned to go ahead and bias my tubes after very change. but there's no tech guy in my town and so I guess I'll do it myself. Is there a thread on the forums that covers this mod in more detail? I searched but couldn't find anything. Thanks for your time 

 

I have not modified my DT-25 head because there is less point in doing that one since the test points and adjustment are fairly accessible...However, I will be modifying my DT-50112 on the next tube change which should be pretty soon as the Mesa tubes that are in there are several years old...

 

I will post a thread with pics and a parts list with what I find when I do my DT50. Basically, you move the points to the rear chassis of the amp and install some panel mount bias pots...It's not so much a modification, but rather a safety improvement to a cost cutting design...Rear points and adjustment pots have to be done by hand and it would add cost to making the amp...There is an improvement to bias stability in the installing superior bias pot(s) that have superior g-shock ratings as compared to the PCB trim pots...Just means they will not drift as easily and the current is more stable under vibration...

 

The only technical measurement that is needed is insuring that you get pots that have at least the same value pot as the PCB pot that is being replaced....The SV had an issue that the pots were a little undersized (5K)...I also had one on my MK1 that was out of tolerance and I could not get to a 70% bias as I needed 5K of resistance and one of the pots would only get down to 4.8K....In terms of test points and pots, this is not different than an SV, those were not designed to be modified either...

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I will post a thread with pics and a parts list with what I find when I do my DT50. Basically, you move the points to the rear chassis of the amp and install some panel mount bias pots...It's not so much a modification, but rather a safety improvement to a cost cutting design...

I'm assuming the procedure is the same for the dt-50 and the dt25 combo (like mine) Are the parts the same? I will be anxiously awaiting your post. Thanks for your time.

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The hardest parts on the SV were drilling the 5 holes in the chassis for the pots and points....The points are generally easy to wire...It's getting the pots off the PCB where some PCB experience is helpful...after that it soldering an dressing 7 wires and putting it back together...I am guessing the DT50 has more space in the chassis than a DT-25 combo...

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I totally overcame my fear and changed and biased my DT-25 amp. Piece of cake! I made a video and posted it.

 

Replacing and biasing tubes in the DT-25 combo amp. 

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