kawititnow Posted December 14, 2016 Share Posted December 14, 2016 Hey everyone, This is my first time swapping out tubes. I ordered a matched set of EL34's with 24-hour burn in. I put the new tubes in, let it sit in standby for a few minutes, took it off of standby. I measured the bias on V2 and adjusted to 25 mV, I then measured V3 and was reading 35mV. I adjusted it to 25mV and then measured V2 again and it was 15mV. So basically I have a 10mV difference between the 2. I assume this is not normal. Any way to adjust them independently? Quote Link to comment Share on other sites More sharing options...
psarkissian Posted December 15, 2016 Share Posted December 15, 2016 Are you using the specified Electro-Harmonix versions of the tubes? It's not an all analog tube amp, so using the specified tubes are recommended. Also check with the Knowledge Base here on the Forum regarding bias voltages. Quote Link to comment Share on other sites More sharing options...
kawititnow Posted December 15, 2016 Author Share Posted December 15, 2016 Are you using the specified Electro-Harmonix versions of the tubes? It's not an all analog tube amp, so using the specified tubes are recommended. Also check with the Knowledge Base here on the Forum regarding bias voltages. Yes Electro Harmonix brand Quote Link to comment Share on other sites More sharing options...
kawititnow Posted December 15, 2016 Author Share Posted December 15, 2016 I just looked at my receipt and thought that I had purchased a matched set. Turns out they weren't a matched set. Quote Link to comment Share on other sites More sharing options...
Brazzy Posted December 15, 2016 Share Posted December 15, 2016 Hey everyone, This is my first time swapping out tubes. I ordered a matched set of EL34's with 24-hour burn in. I put the new tubes in, let it sit in standby for a few minutes, took it off of standby. I measured the bias on V2 and adjusted to 25 mV, I then measured V3 and was reading 35mV. I adjusted it to 25mV and then measured V2 again and it was 15mV. So basically I have a 10mV difference between the 2. I assume this is not normal. Any way to adjust them independently? As far as I know there is no way to adjust them independently. I did the same thing you did when I had an issue with sound fading off after 15 minutes of play which culminated into no sound all together. All the fuses checked good so I ordered an ultra matched set of EH's and after making the bias setting had 4mV difference and I thought that was abnormal. I was thinking the tubes should read the same but I suppose they don't most of the time. I'm not sure what the bias was new since I wasn't equipped to check it. I had another problem anyway which Line 6 fixed. Quote Link to comment Share on other sites More sharing options...
psarkissian Posted December 15, 2016 Share Posted December 15, 2016 Matched set is a must. And be certain you have a stable AC main voltage when doing bias on a tube amp. 10mV difference is a bit too much. From the Knowledge Base--- DT25 bias is 25 mV +/- 3 mV. Quote Link to comment Share on other sites More sharing options...
Brazzy Posted December 15, 2016 Share Posted December 15, 2016 I just looked at my receipt and thought that I had purchased a matched set. Turns out they weren't a matched set. That sucks. Quote Link to comment Share on other sites More sharing options...
psarkissian Posted December 15, 2016 Share Posted December 15, 2016 Yeah, sucks. Take them back, see if they'll exchange it or something. Not having a matched set would be too unstable, like running a hot rod car at near red line,... with a mal-adjusted timing belt. 1 Quote Link to comment Share on other sites More sharing options...
kawititnow Posted December 19, 2016 Author Share Posted December 19, 2016 So I got a new set of MATCHED EL84's from Tubedepot.com (I highly recommend them) They are cheap and reasonable!! Nonetheless, I put them in and they each biased to 25 mV +/- 0.5 mV. Quote Link to comment Share on other sites More sharing options...
psarkissian Posted December 19, 2016 Share Posted December 19, 2016 I hope they are EH brand EL84's. These amps are not forgiving of modifications. They might come highly recommended for general use, but are they, when it comes to a DT amp? These are hybrid amps (analog and digital sections), so you can't do tube swaps like we use to do in the 1960's and 70's, on an all analog tube amp. Quote Link to comment Share on other sites More sharing options...
kawititnow Posted December 20, 2016 Author Share Posted December 20, 2016 I hope they are EH brand EL84's. Yes, they are matched Electro-Harmonix EL84's. Quote Link to comment Share on other sites More sharing options...
psarkissian Posted December 20, 2016 Share Posted December 20, 2016 :) Quote Link to comment Share on other sites More sharing options...
CraigGT Posted January 22, 2017 Share Posted January 22, 2017 So just for future reference, how do you check the bias voltages on a DT25? Craig Quote Link to comment Share on other sites More sharing options...
psarkissian Posted January 23, 2017 Share Posted January 23, 2017 Best to have an authorized service center do it, as they will have a VariAC and service info to properly calibrate and bias with. Quote Link to comment Share on other sites More sharing options...
radatats Posted January 24, 2017 Share Posted January 24, 2017 So just for future reference, how do you check the bias voltages on a DT25? Craig If and ONLY if you have previous experience and skills working on tube amps you might find this link helpful. Voltages in there can kill you so be careful. http://line6.com/supportarchivenew/thread/75238/ Quote Link to comment Share on other sites More sharing options...
psarkissian Posted January 24, 2017 Share Posted January 24, 2017 Most definitely radatats. I've been dealing with tubes (valves) since my teens, 40+ years,... ... I still get zapped from time to time. And it hurts. Can't emphasize that enough. Quote Link to comment Share on other sites More sharing options...
CraigGT Posted January 29, 2017 Share Posted January 29, 2017 Thanks, it was more curiosity than anything else. I am an engineer by trade and I know that valve amps can bite very hard. I have a Burman 502 combo which is in need of some tlc but it's far too scary for me :-) Craig Quote Link to comment Share on other sites More sharing options...
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