psarkissian

And as far as tubes for DT series amps go,... stick with the EH version from Electro-Harmonix. And before someone says that all an EH is, is a Sovtek with EH painted on it,... EH owns the Sovtek factory in Russia. The EH's are further scrutinized premium versions for clients like us who want a level of reliability in the tubes we get. I pushed for better QC in tubes a few years ago with the Spider Valve series, and that's carried on to through to the DT series. Mike Matthews (owner of Electro-Harmonix) sees to it that QC is top notch with the EH series tubes. I talk with him about this every year at the trade show. He's quite the gadget geek.

The specified bias is what's optimal, that's why it was set as the bias. It has nothing to do with running cooler. Bias is used to keep the signal and the transfer function within linear regions to prevent non-linear distortion. Under biasing is just as bad as over biasing. Under bias can also lead to drop-outs at certain frequencies at certain power levels. Not to mention the non-linear distortions. The 70% solution is useful in 1960's analog tube system with one gain topology. This is a hybrid system with four topologies, and can not be treated the same way. Use the specified tubes at the specified bias and everything runs well. Bogner designs are very unforgiving when you try to go outside of the specs. I have these kinds of talks with all the tube people (Bogner, Pittman, Matthews, et al) at the trade show every year. My expertise,... this is not a 1960's one topology analog tube system. Don't mess with it, stick to the specs.

"From there, math and Ohm's law tells me where to set my 70% bias for my DT. Izzat about right?"---- Sort of,... at least for an analog tube circuit like the old Fender circuit schematic I saw in an earlier post. Can't treat a hybrid like this with a mix of analog and digital, in quite the same way as the old 1960's/70's amps. It's an assumption that gets people in trouble, and gets their amp onto my bench. It's an amp, play some rock music thru it,... don't mess with it.

If I recall, there should be a value in the Line 6 Knowledge Base for the bias, so that there won't be a need to mess with the plate voltage. http://line6.com/support/page/kb/_/amplifiers/dt50dt25/dt50dt25-faq-r144

Smashcraaft,... China Variax 600??? You sure it's China? The one we use for testing, in our repair lab, says Korea.

"I'm guessing you're probably under corporate obligation to dissuade modifications for liability purposes"---- No. I'm under no obligation to be here at all. I'm a tech,... here on the forums as a courtesy. I'm trying to keep everyone's gear from ending up on my bench. I've been dealing with tube electronics since the 1970's. There are those out there who may know a thing or two. There are also those who don't, and they are the ones I worry about. Trying to keep your product experience a positive one. I see too many tube amps end up on my bench because someone didn't take my advice. Just trying to keep everyone's gear from ending up on my bench. I don't need the extra job security (for anyone wondering).

After all is said and done - that's really the only way to buy. Thanks for the comment. TW ================================================= I don't know if it's the only way to buy, but it's how I've done it, and been satisfied. None of my guitars were brand new when I got them,... including the four JTV's I have. I played them, spent time with them, got to know the in's and out's before I got them. Never had a problem with any of them. But then, I've been repairing, rebuilding and maintaining guitars since I was fourteen. Studied music, electronics, physics and acoustics,... so it comes natural to me.

TW: "... maybe they will resurrect the JTV as some have alluded to"--- Not gone yet. There's a run of 2016's out there. Regarding buying,... I play it. If I like it, that's the one I buy,... not the one fresh out of the box from the back, but the one I'm playing that I like.

Yes,... what spaceatl said. As soon as you put a power tube in and power up, there is a current running thru the primary side of the transformer. If the secondary isn't correctly loaded on the output, the transformer fails at the primary. I've seen red plating, blown impedance matching and power tube plate resistors burned. Best leave it to the pros. Would hate to see someone void their warranty 'cause they got curious or wanted to hot rod an already hot rod. And these are hybrid amps, not like the analog tube amps of the 1960's. These Bogner designs are not forgiving when it comes to mods or hot rodding, like tube amps of the 1960's. And Rheinhold Bogner is already a hot rod master of tube amps. So stick to specified tubes. For those unaware of the source of the term "hot rod", it comes from the 1950's and 60's. Tricked out race cars had engines where the intake, exhaust and piston rod got hot when racing. To "throw a rod" is to have a rod break down in the engine, and sometimes blow thru the engine block (throw a rod), and "blow the engine" in the process. It's not pretty, and is very messy. So, please don't "throw a rod" in your Bogner design L6 tube amp. And don't void any warranties.

"The bridge plate on my 500 certainly is grounded"--- Wouldn't surprise me. Carlos Rios' Frankenstein SG copy has a 500 bridge going to some JTV electronics, that had to be grounded lead at the bridge plate. While Stevic McKay's custom guitar with JTV electronics had to pull the bridge post ground lead because it created a passive loop. Depends on the overall circuitry. All the grounds have to be grouped and tied off in the correct way. Very good Charlie.

"I would have thought that the bridge was earthed though"--- Only needed with guitars that have pick-ups. Piezos are usually grounded thru the saddles. So bridge plate on a 500 shouldn't need bridge grounding.

Don't recall us ever posting plate voltage info, since it's not something for end users to be messing with in the first place.

http://line6.com/software/

Can you upload a screen shot? The latest for JTV and Standard is v2.21 firmware. Is the icon on the left of the screen a Standard or JTV?

There is no user access through the ports to the plate voltage for good reason, it a High Voltage Shock Hazard. And there's no reason to be going to the plate voltage. In school, they teach us us to stay away from the plate voltage, it hurts when you get zapped. It's High Voltage, stay safe,... leave it alone. Been doing this this more than four decades, and was trained by top people in this profession. And if I slip, I still get zapped every now and then. It hurts, leave it alone. Don't do that.

With the DT25 there are ports for you to put your meter probes into for metering the voltages for biasing. DO NOT go directly to the sockets to take measurements. This is High Voltage stuff,... leave it to the pros.

Start by using the correct Line 6 power supply for that product, for your region. When that's done, if still has a problem, post a jpeg photo or a video of what the screen is doing.

Full Compass shows one for the JTV-59 and JTV-69, but none for the JTV-89. You may have to special request the 89 jack plate. The connectors may be the same, but the curvature of the plates and cable lengths are not the same. I've worked on hundreds of JTV's,... it will make a difference in regards to fit and function. Make sure you get the correct one from them,... 50-04-0079-2. It will make a difference.

"... when variax system turns on, mag pickups doesn't interrupt and affect"--- The pick-ups are not engaged in Modeling mode, but the magnetic field of the magnets is always there. It's what magnets do, there's no way to turn that off. The signal from the pick-ups may not be there, but the pull from the magnets always is there. Also there is intonation to consider, if it's not spot on, a number of frequency artifact can occur, and the Alt Tune will bring them out more,... including something called "dual tone effect". That occurs when you hear both the note coming from the string and through the amp at the same time. The strings are standard tuned, while the amp signal is Alt Tuned. The non-stock pick-ups just complicate things more. It needs to be dealt with by a factory authorized service center that knows the product. It's not the usual guitar that just any guitar repair person can deal with. Needs to be looked at by someone who knows the technology. And I'm available to those authorized techs to consult should they require it, since I have worked on hundreds of these. They will know how to contact me should they need it.

At this point I recommend logging a support ticket in your account.

Flash update was done, so that possibility is eliminated. One of the pick-ups is set too close to the strings. Magnet is then allowed to pull on the strings inducing a warble affect. This can be exaggerated in Model mode, and further exaggerated in Alt Tune. Pick-up height should be checked and adjusted. The set-up in general should be double checked and adjusted as needed. The audio suggests it’s on the edge of fret buzz, which can further complicate the warble effect. If a pick-up is not a stock pick-up, then this complicates it even more, and the usual height setting will have to be altered. Judging by the serial number, this is an older unit, so I don’t know when a full set-up was last checked or done to it. So far, from what I've heard in the audio, everything points to a set-up issue. That's where "warbling effect" usually comes from.

In a nutshell,... Using battery and VDI at the same time has been a problem on and off in the past. So,... don't do that. Use one or the other at any given time.

When the diode conducts and you have voltage build up coming the other way in a circuit, while the diode is on (conducting), as in volts from VDI one way and battery volts from the other,... there is an opportunity for the diode to fail. And it usually does. I've seen it happen. Used to do this in school as a test to see how diodes fail. It's why 700 Electric boards were later revised.

Some basic ones have 75V PIV. But that also assumes volts coming from one side of the diode at a time. Battery AND an XPS or VDI,... at the same time,... volts coming from both sides of the diode, while the diode is on,... poof! Failed diode. Even worse for Schottky and Germanium diodes. It's not going to handle volts from both sides at the same time. Same with the 700 Electric.

Diode is a one way valve. Peak Inverse Voltage (PIV) is the maximum voltage that can be sent in the inverse direction before the diode fails. Too much voltage beyond that, and it overwhelms and breaks down the volt barrier,... and the diode fails.