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Biasing The Dt50 212 Combo


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Hey Guys,


I've been searching high and low for a proper step by step,instructional kinda video/manual,  for biasing the tube power section for the Line 6 DT50, but to no avail.


I think it's high time, the forum have something like this in place so we can do the maintenance ourselves. Last i check, it cost nearly the price of a single tube to send it to the amp tech for biasing...



Hope any guru out there can help? =)

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google is your friend. took less than 10 seconds to locate the following...


I replaced the tubes in my DT25 a few months back and found the biasing procedure to be fairly straightforward, completing the process in about 30 minutes. the hardest part was removing the amp from the cabinet so I could reach the bias pots and measurement contacts.



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The voltages in these amplifiers can kill you joke...If you are not sure how to do this or experienced working around hot current, take it to a tech...If you go for it, always adjust with one hand and the other hand behind your back...really, I am not kidding about that.

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Thanks for the tip guys. Appreciate it much. I did come across that thread mention, but i am thinking of something somewhere along the line of a video tutorial, or something with pictures, indicating step by step, what to do, what to touch, and what NOT to touch. As mention by spaceatl, it can really kill is precious...and i don't wanna loose mine just =P


That thread also did mention of using a Dual Bias Tester. Is there anyway to bias the amp without needed to purchase the tester? 

Just wondering if anyone has done it with just a screwdriver to adjust the pot and also plus with just a multimeter... ?

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The thing is, adjust bias properly means using an O-scope and a tone generator...The whole point of adjusting the fixed bias mode of the amp (Class AB) is to minimize the notch of the sine across the x-axis in order to minimize x-over distortion...One thing to keep in mind is that if you always run the amp Class A, there is no need to adjust the bias...


Line 6 provides test points and pots on the board usually...I can't really comment on the DT25 combo as I have the head version...But I have an SV MK1 and MK2 which are similar in terms of requiring the chassis to be pulled....I modified both of my SVs to have rear panel test points and basically you just use a multi-meter and never have to open the amp...It's about $7 in parts from Weber and any solid tech should be able to do the mod for you for the bench fee (usually 1 hour of labor)...To me that is money better spent...just modify the amp so you can do it yourself safely and on a gig...


So I dug this old thread up about the SV mod...A DT-25 mod would be very similar...

Edited by spaceatl
Added Old Bias Mod Link
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