mtreehugger

The problem with that is that he doesn't tell you when to put the tubes back in. This occurs sometime before "let 'em cook," obviously. I think even in the original thread, which wouldn't be too hard to find as it was only a few days ago, that wasn't clear. You didn't say, but what follows is assuming that you were in Class AB and will continue in class AB. Thing is, the bias is supposed to remain the same (in Class AB, natch) no matter which voice you are in (at least, that's what I read here in these pages). When you went to V3 something happened. Was it just a fluke, or was it something else? For example, is it possible to have a bad board that causes your tubes to red plate in voice 3 or something along those lines? For you, the thing would be to power up with the bias pot turned all the way down and no tubes in. Then at that point--assuming that you are a certified electronics technician and are trained so that you aren't putting your life in peril (or your amp), you would probably want to compare those voltages in voice I and in voice III. If the bias voltage isn't constant, then based on what I've read, I'd say there must be something wrong with your electronics. If you're at all unsure about what you're doing, you should take it in to a Line 6 service center. If it's under warranty, then absolutely don't mess around or you could void your warranty. Also, ONLY USE A MATCHED PAIR OF ELECTRO-HARMONIX TUBES IN THE POWER SLOTS!!! It has been well-stated here that any other brand of tube may lead to problems. I'd recommend searching out the recent threads about tubes and reading the warnings.

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

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.

Great post! Just looking at it, I'm guessing your noise got cut in half or better. I'm hoping I get my amp back next week (miss it dearly), but whenever I do finally get my hands on it I think I'll give those tubes a try!

Is that voicing II? Most folks, myself included, report the most noise in voice III, which also (not coincidentally) has the highest negative feedback. (Voice IV is a "modern feedback" which means something along the lines of certain frequencies getting more negative feedback than others, but don't quote me).

Ahhhh... Thanks! It's unlikely that I'll want to be that technical in my approach. Although... I do have an oscilloscope that I "stole" from the auction back when I was in electronics school that seldom gets used... So after you arrive at your starting point--which could also be taken from the Line 6 specs (25mv & 36 mv, respectively), then do you go to the scope to dial out the notch? Or could a person just kinda tweak the bias to their own liking based on their own ears, providing that they ensure that the bias voltage never exceeds the Line 6 spec? Can a bias that's too low hurt anything other than your tone? I guess I'm also asking, as I have no knowledge, what's the deal with the notch? When I first read about it, getting rid of it seemed to be the primary thing, but most of what I'm reading in these forums lately is absent any discussion of that. I would think that if the bias were on the low side your tone would be cleaner with more headroom, and the amp would run cooler. If the bias was dead-on, you'd have exactly what Bogner wants you to have. If the bias is high, now you're melting tubes, boards, etc. Is any part of that true, or am I way out in left field?

I love what happens when Marty strums his first chord! I think it's in every guitarist's DNA, a kind of racial memory peculiar to six-string slingers to be blown backwards by the blast of your amp, so seeing it with my own eyes on the silver screen was enormously gratifying--and riotously funny!

It's very confusing. And I still don't follow the math: "414 volt plate; 70% of 12 watts = 20.4mv bias target" Okay, you measured 414V, and 70% is a target. I get that. But where does the 12 watts come from, and how can you take 70% of watts and come up in millivolts? Isn't that like saying Jethro dated his grandma so his neighbor gave birth to a pig? It doesn't compute.

so Bogner got these amp's mojo from the non-linear regions?

Innovine, did you find that the JJs had a better noise floor than the EH power tubes? Have you ever tried a different tube in the inverter slot, and if so, did that help with the noise?

You're saying this about the DT25 and not the DT50?

innovine, you got your amp up and running yet?

I had been wondering that myself, until I read your post in the other thread, where you printed that Bogner amps are now using Chinese 12AX7's, and also the piece about their characteristics differing from other tubes. After reading that, my guess now is that due to the slight differences in the amps (EL34s vs EL84s for one), the chinese tube either sounded better or was a better fit in the DT25 architecture than EH or others. The DT50 is an older design, so it could also be that Chinese 12AX7s were not reliable enough at that time for serious consideration, so they tweaked it around the EHs. O'course I could be wrong on both theories...

I filed a support ticket with Line 6. I was asked for and provided a recording of the excessive noise floor and was told it "might be a little high." I called and asked about the ground buzz and was told it was probably tubes. My power is CLEAN. I bought a power conditioner anyway, out of desperation, and this actually produced power that was dirtier than what's at the outlet because the buzz got louder. I took it back and the amp got quieter again. Perhaps you don't realize this, but these symptoms are present in all amps, it's just a question of degree, and with the DT we are told it's high gain so it will be noisey. (which mine definitely is/was) My amp is now in the shop awaiting service due to the above and the fact that it's in the series where it may have the bad transformers. I believe I forgot to mention excessive heat here, but it's on the list to be looked at as well. The reason I wrote what I wrote was to give Psarkissian a chance to correct me if I was wrong. If those symptoms do not lead to amp breakdowns--and I hope they don't--then we don't have to chase ghosts, wonder where to draw the line between normal and abnormal, or wonder if we're damaging our amps by just using them.

Spaceatl, I thought I read that Class A amps burn through tubes very quickly compared to Class AB. Is that true? Sorry, but I don't follow your percentage calculations--was this info meant only for people who are well versed in tube amplifier theory? You've most likely seen the strong advocacy here in this forum for using only the spec bias and EH tubes and such. However, you've been running yours much cooler (@ 20.29 mv?). If all a person has is a voltmeter, will the tubes last longer at a lower bias voltage? Are these hybrid amps, with ICs and PCBs, more or less likely to fail and need repair if they bias their tubes to a lower voltage than spec?

Well that seems simple enough. So I'll play my heart until until such time as I hear volume cut-outs or crackling noises, and when that happens I'll have the tubes swapped with only EH and make sure they bias a DT50 at 36mv or a DT25 at 25mv. I will not worry if I get white noise, high noise floor, or a ground buzz with no guitar cord plugged in. That takes a load off my mind. THANKS!

Spaceatl, thank you so much!!! Question: Line 6 warranty info states that an amp that has been repaired or has had a repair attempted by anyone other than a Line 6 authorized service center will not be covered under the warranty. So if a person wants to put in their own tubes, did they just void their warranty? If a person biases their power tubes, is the warranty voided? If a person measures their bias voltage, is that an "attempted repair," and thus their warranty is void? I have come very close to doing these things but do not want to void my warranty.

Holey moley! I bought an 8-month-old DT50-112 3 weeks ago. First time I played it at home I determined that I should have bought one when they first came out, and that I'll never be without one ever again--the tone is that good! Not good, sublime. The next day I started noticing symptoms like over-heating, excessive noise floor, ground buzz (even with no cord plugged in), and learned that my amp is part of the series of amps that are implicated under TSB 059. And it's now been in the shop for one week. After reading your saga and that you just got your amp back, my mind is blown, and my heart sunk. What have I gotten myself into??? I had reservations about modern tube amps (having owned a Dual Showman Reverb for over 35 years with absolutely no issues other than dirty pots), but this is worse by far than any worst-case scenario I could previously have imagined. Thanks for sharing your experiences. I SURE HOPE YOUR LUCK IMPROVES... ...AND THAT I'M LUCKIER THAN YOU WERE!!!

Thanks again! We really appreciate your info! You're our only source for this kind of knowledge, it seems. Being that tube life seems to vary so dramatically, the advice to change them out "regularly" seems too open to interpretation for my comfort level. I hope it's okay to ask just a few more questions! 1) How safe are our amps if we only use EH tubes biased to the Line 6 voltage spec? 2) What is at risk during normal operation and ownership (i.e. what can still go wrong related to tube failure--using EH tubes, of course)? 3) What are the warning signs that a problem might be developing (i.e. how do we know when our tubes MUST be replaced or bad things will happen)?

This is really helpful information--THANKS! Looking at the other side of the equation, what can go wrong if only EH tubes are used? Folks report that EH tubes can expire anywhere from 3 months to 2 years, some have actually melted glass, and I believe I read that some have red plated as well. Information like this suggests that it would be folly to assume that EH tubes are rock-solid, that nothing can go wrong as long as these are being used. Rather, it would appear that as tubes break in after initial biasing, and as they age, the potential for resulting damage to a DT from what would seem to most guitar players as normal usage is very real. Can you tell us, how safe are our amps if we only use EH tubes biased to the Line 6 voltage spec? What is at risk during normal operation and ownership? What are the warning signs that a problem might be developing? What precautions can we take to ensure that our amps don't wind up on your bench? THANKS!

THANKS FOR THE INFO!! Just to be sure I understand your answer... Can damage to the printed circuit boards and/or their components occur without the tubes red-plating?

Psarkissian, could you please expound a bit about what goes wrong when other tubes are installed to the EH spec? I follow you when you say that they wind up on your bench, but what is it that specifically goes wrong? Do the tubes get too hot and cause the board to melt? If not that, what? THANKS!

The more I hear, more inconsistencies crop up about going strictly with EH tubes.

Geez--all the chewing out we get about not using EH tubes and/or having a Line 6 authorized service center bias them for us... And this happened to you? Wow! No wonder they're so willing to give you a price break, they shoulda known about the Line 6 party "Line" (no pun intended).

awesome! can't wait to hear.