mtreehugger

So my tech calls me up and tells me that he observed the same voltage change that I did, however, he also observed that when switching to voice III my amp was also switching to Class A. And in class A, 18 volts at the bias test pins is normal. I had no idea my amp was doing this, but answers from another thread of mine by Phil (Phil_M I think) tell us that the FW 2.0 update changed it so that each voice will "remember" the Class and pentode/triode settings so that if you switch voices and then go back it's where you last left it. I familiarized myself with the amp under FW 1.x and was unaware of the functionality change that took place after I did the update. So I'm in there, measuring the voltage, completely oblivious to this, and unable to see the front of the amp. Dang good thing my tech spotted that--he's a keeper!

I checked it all out at v1.x, when I first got it, so I'm sure I noticed how it acted at that point, and never suspected it would act any differently after the FW update...

Great answer, Phil! Hope you don't mind my giving "credit" to Palico, who is less-recognized than you. Wish I could give it to you both! Thanks for the help!!!

This is a follow-up to my earlier post. Does anybody know--does the voicing switch remember other topology settings? What I mean is, do the voices act somewhat similar to the way the channels act in that when you switch out and then switch back in it remembers the last setting? So, for example, if you set voice II to class AB, then go to voice III and set that to Class A, then if you go back to voice II, will your DT automatically switch back to Class AB? My amp is in the shop and my tech is telling me this is what it does, which is news to me. He believes that each voice will remember the class switch and the pentode/triode switch settings. I re-read the quick start guide and it seems like maybe this is what it says too, but I'd really love to confirm it. THANKS!

I got ahold of the tech 1 hour after posting this. He said that according to the schematic, what I'm reporting is impossible without frying resistors and tubes and junk, which is pretty much what I'm afraid of. I'm bringing the amp back this afternoon and he'll verify my measurements. He'll expedite this to the best of his ability, and hopes that Line 6 is able to expedite whatever they may need to do as well.

Can anybody tell me if it's normal to have a radically different bias voltage for voice III. I'm in Class AB (of course) pentode mode, and in voices I, II, and IV both pins check in at 35mv ±1mv. But when in voice III, the voltage freaks out. I'm actually measuring 18 Volts, which is 500 times as much voltage as the other voices!!! I just got my amp back from the shop. I had asked the tech multiple times to check this but apparently he failed to do so. After replacing teh DSP board, he said he tested it thoroughly and gave it a clean bill of health. ??? It occurs to me that if voice III is actually Class A or somesuch that this condition could be normal, however, without any knowledge that it is normal I'm not going to operate the amp. Another possibility is that the voltage I'm seeing at the test pins with my voltmeter is not what the tubes are actually seeing in voice III. Neither of these notions seems likely, though. Can anybody check their amp in this regard? (remember, I'm checking at the test pins) THANKS!

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?

Thanks for the update, DarrellM5! So both fuses blew and you sent it in for warranty service. I'm curious, did you call and they suggested this, or was it your idea to get it checked out? Weird that they didn't send a note along with, I guess they want customers to call in. They have a good policy about that, even extending beyond the warranty period (although it takes time to get through).

After reading your thread, I now know that it's the "analog board" that has the tubes. I do suspect an issue there as well, so unfortunately I could be waiting, and waiting, and... But anyway, thanks for the excellent comment!!!!!!! ...ever thought of installing a small cooling fan inside the metal box of your combo amps? Seems ridiculous to me to have all that heat spewing off those tubes and rising right into those sophisticated electronics. Can't figure out why a fan isn't there already. Just sayin...

What a totally awesome post! Am I weird for enjoying the read? (I've got an AA in ET, so maybe that explains it?) You're right--you are lucky to have 2 DT50's! And while most of us won't be able to simply swap boards like you did, it's good to know that bad diodes can cause stuff like this. THANKS!!!! This is good stuff to be able to access when my warranty runs out!!!!

excessive heat to the point of stinking, excessive noise, ground buzz, and it's in the range of s/n's affected by tsb 059. apparently there was more wrong than i knew, as i didn;'t notice anhyting related to what the tech found.

I'm surprised to read that a firmware update is needed to enable the silent recording option! As for the need to have a POD HD, I suspect that this might not be needed. It would make more sense from a design standpoint to have this particular functionality be solely an amp thing. After all, the switches that pertain here are on the amp and not on the pod, so why would the designers require a POD be connected? I think it's just that the only place this functionality is documented is in the POD HD connectivity guide for DT, so it was written the way it was--but that's just my guess and I can't test it because my amp is also in the shop.

Got a voice mail from the shop today on my DT50-112 (after 2.5 weeks). He says my amp is "a pretty strange one there." Control signals are either getting mixed up by the DSP or they're coming out of the DSP wrong. Low power mode is sometimes more like high power mode, actually (depending on the topography is what I think he meant by "sometimes"). Line 6 advised him to replace the DSP board, which is on the way and should be here in a week. If that doesn't cure all my ills, then probably relays or...?, he said. That doesn't seem quite like the issue of TSB 059, does it?

Got a voice mail from the shop today on my DT50-112 (after 2.5 weeks). He says my amp is "a pretty strange one there." Control signals are either getting mixed up by the DSP or they're coming out of the DSP wrong. Low power mode is sometimes more like high power mode, actually (depending on the topography is what I think he meant by "sometimes"). Line 6 advised him to replace the DSP board, which is on the way and should be here in a week. If that doesn't cure all my ills, then probably relays or...?, he said.

You can totally do what you want if you have a POD HD and L6 LINK. From the DT50 L6 LINK Connectivity guide...: Direct Out The DT amplifier’s DIRECT OUT continues to function as an analog output with L6 LINK in use. Use of this XLR output is recommended to feed your “fully baked†POD HD + DT amp tone to an external recorder, mixing console, etc. Since the audio signal fed to the DT amp via L6 LINK is a mono signal, this Direct Out is a mono signal as well. Note that the Direct Out functionality differs based on the DT amp’s LOW VOLUME MODE (see page 4•3) and STANDBY switch settings: • Low Volume Mode Off, Amp in Standby = The DT amp’s Direct Out is disabled. • Low Volume Mode On, Amp in Standby = Direct Out signal consists of the “Full†(preamp + power amp) Amp Model with no analog amp. This is a handy option for “silent recording†while still providing the tone of a cranked amp. • Low Volume Mode Off, Amp On (not in Standby) = Direct Out signal consists of the “Preamp†Amp Model with the analog amp. • Low Volume Mode On, Amp On (not in Standby) = Direct Out signal consists of the “Full†Amp Model and the analog amp. My guess is that you can do a direct out even if you don't have a POD. Try putting it in standby and in low volume mode (Volume knob pulled out, I believe) and see what you get.

I have a full set of replacement tubes that I haven't installed. When I sent my amp to the shop, I decided to let them install their own tubes if that's what they found was needed. That way the tubes are covered for 90 days, which is about when the 1-year warranty runs out too. The shop charges about $10 more for each tube compared to online prices, which isn't easy to swallow if you're a bargain hunter like me, but this is the least complicated route right now. As for my DT50 in particular, I'm now even more convinced that it isn't just tubes, because as of Thursday they were supposed to call me Friday or yesterday and they did not. This leads me to assume that parts are being ordered. If they don't call me Monday, I'm calling them for another update. Will keep y'all posted!

Seems like they did a very quick turn on your amps! I believe that if a Line 6 authorized service center sells and installs your tubes, there's a 3 month warranty.

Wow! That certainly is useful! Thanks! Great job googling that tidbit!!! So then the relatively simple method involving a voltmeter would seem to be the only way to go. It's strange that actual Line 6 employees have stated that O'scopes must be used by Line 6 authorized service centers whenever tubes are to be replaced.

Something strange is going on then. That quote was taken from "L6 LINK Connectivity Guide for POD HD & DT Amplifiers v2.10." If I had my amp I could test it, but of course the shop is running behind...

If you run the L6 LINK, the POD HD master volume has no effect. From the connectivity guide pages 2-5 and 3-7: "The POD HD Master Volume has no effect on the signal fed to the DT amp. Simply use the amplifier’s Master Volume knob to control your overall volume." Further, while I can't explain why, the HD just plain sounds much better with the volume at max than it does at a lesser volume. I experienced this myself in studio/direct mode, and other have as well, some I believe were using the pre's. I would guess that the noticeable effect of turning up the master using some connection other than L6 LINK could seem like one was getting some preamp OD from the pod. Are you using the default doubled input or is it adjusted to provide just a single signal path? How is the HD hooked up? What mode is the POD in? There are so many variables here! When I record direct from my HD500, my Tascam US-800 likes it better if I turn down the master. I forgot to turn it back up once when I went back to my normal FRFR system and it took a few days to figure out why my guitar abruptly started to suck sound-wise! Personally, after having experimented a bit, I would never again use the HD without the L6 link. The tones are incredible, to heck with the master on the HD.

Whatever happened to the idea of adjusting bias using an O-scope to dial out the "notch?" Actually, spaceatl, you're the only source I've run across that specifically mentioned the notch (although my research has been anything but thorough). Is having a notch in your output sine wave maybe not so bad or even desirable to some? Please elaborate on this if possible. THANKS!

They have that already (computer-like circuits that emulate tubes). They call it POD HD, and it's fully compatible with your DT! (sorry, couldn't resist)

I really hope I didn't pass along faulty info!!! I inferred that it's possible check the bias voltage with no power tubes in the sockets. I wouldn't think that would be completely accurate, but I thought it might tell him if something is wrong with his electronics. What say you? (something happened when he changed from voice I to voice III) As for turning the bias down all the way, that doesn't hurt anything does it? (other than provide for a cold, sterile sound).

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).

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.