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psarkissian

Tubes

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Thank you very much for this answer. Understood, at least partially.

 

Not quite sure whether I do understand the part of the 'nice talk between the analog and the digital section' and the 'bad things that can happen'. As an electrical engineer who spent his whole career in R&D departments developing electronic instruments in EU as well as in the US, I would say it would not speak for a robust design if the 'curves of the tubes' would influence the digital part so that 'bad things can happen'...  Nevertheless, there's too little robust information/data available - and I guess that's the plan and I understand this in terms of intellectual property. I was just hoping to get a little more background information...

 

I folllowed one of the links in earlier posts of this thread an ordered the EH version of the EL84 in Germany.

 

https://www.banzaimusic.com/EL84-EH-Platinum-Matched.html

 

Price for a matched pair is just 25,22 Euros - which looks very reasonable to me if I compare it to other flavors of the EL84 mentioned above and been given the information that this is a premium version of the SOVTEK tube.

 

So, I do hope they will do it!

 

Thanks again and best wishes from Germany.

 

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" Not quite sure whether I do understand the part of the 'nice talk between the analog and the digital section' and the 'bad things that can happen'. " ---

 

There is a digital processor board for effects and aspects of the "Topology" settings along with digital circuits on the amp board.

The digital half has expectations from the analog half, and the analog half expects certain things from the digital half. Anything outside of that,

and it can go too nonlinear, too soon and easily. That distorts, and distortion of that kind is bad. There's good distortions and bad distortions

in tube amps, so one has to be careful.

 

Also, they have to be matched pairs, and should be biased by a Line 6 authorized service center, as this amp series has not just a bias,

but also tests and checks to be done to check bias and gain transfer functions. Spider Valves don't require all that, but the DT Series does.

And if a service center needs to consult me, they can through normal service center channels.

 

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Thx, again. But more answers -> more questions ;-)

 

Tubes have to be matched pairs - that's clear. I am curious though, what these additional tests and checks would be beside biasing - can you shine a little more light on this? Looking at the amp, I do see the testing points for bias and also I see the 'bias adjustment hole', assuming there's a potentiometer behind it. I can't see anything more. So, does that mean you would perform some kind of digital / software checks and adjustments, probably through midi ports (since there is no other digital interface available)?

 

Please understand that taking the amp to a service center is not trivial for your customers. There is only one center in Germany. Driving 400km to drop the amp there, 400km back home again, and two weeks later the same to get the amp back means travelling 1600km's. Shipment is also difficult and expensive due to the necessary packaging and the weight of the instrument. And this is the same in the US, by the way, as several posts in this forum pointed out already. Having to do this once a year to get the tubes changed is not customer-friendly at all, and, honestly, if I had known this before, would have prevented me from buying this amp.

 

Why does line6 not open up this book of secrets to let more technical experts get the ability to do this job like other companies do?

If pure safety issues are line6's concerns - it is clear and understood that only experts w/ electrical background may do the job - but this is true for many repair and service jobs and a safety hint in the manual is enough to put you on the safe side.

 

Don't get me wrong - I like the amp, it sounds really awesome, I do like line6, I have several instruments in the meantime. But if it turns out that after-purchasing-costs become infinite that's a good reason to look for alternatives...

 

Regards

Wilfried

 

 

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"... what these additional tests and checks would be beside biasing - can you shine a little more light on this? " ---

There are multiple topologies (I, II, III, IV), as well as amp class (A, A/B) and whether running in triode or pentode modes.

These all have to be checked, and when done, the bias has to be checked again after warm-up and tests. It's an all around performance check thing.

 

Second question about tests,... no. That's as deep as I 'm allowed to say about that.

 

Service centers,... wish there were more. It's not just the distance, out of warranty units means a repair cost. Those who

get the sound they are going for tend to find it worth it to them to get it repaired right by the right people to do the job.

 

" Having to do this once a year to get the tubes changed is not customer-friendly at all, and, honestly, if I had known this before, would have prevented me from buying this amp. " ---

I get that. Some can stretch it out to between 18-24 months, depending on  how much and how hard they use it. It's the nature of tube amps in general.

Like tape recorders back in the day, they all need their periodical maintenance and calibrations to run well (serviced thousands of those over the last five decades).

Something like the Spider Valve (112, 212 and HD-100) don't require the same post bias tests because there's no topology or amp class to test for. Bias, check

functions and gains, then let it sit for an hour with signal going thru it. With those, the same tube replacement intervals still apply,... it's a tube amp.

 

Going through the bias and test procedures on a DT amp is to also insure good performance, and that the tubes don't wear too soon.

 

" Why does line6 not open up this book of secrets to let more technical experts get the ability to do this job like other companies do? " ---

Too much proprietary and intellectual property (IP) in this stuff. I know, all those other tube amp companies of old have the schematics out there,

but then, their patents have probably already run their course and are now considered public domain.

 

" If pure safety issues are line6's concerns - it is clear and understood that only experts w/ electrical background may do the job " --- There's that too.

Tubes amps are a big shock hazard. I still get zapped every now and then if I slip and touch the wrong thing, even after five decades.

 

" but this is true for many repair and service jobs and a safety hint in the manual is enough to put you on the safe side. " --- Unfortunately not enough.

And there are a number of people out there who tell me what techs or engineers they are (which we have no way to vouch for), who get in too deep,

then their gear ends up on my bench two weeks later,... sometimes worse off than it was originally.

 

So between the IP issues and safety issues, we always recommend using authorized service centers. In the end it ends up being worth it.

You wouldn't have a janitor with no medical experience do brain surgery on you, you get someone trained and with lots of surgeries and experience

behind them. Same here. Besides,... getting zapped by a tube amp hurts. 

 

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Thx again for the comprehensive answer - this helps a little ;-)

 

Another thing that crossed my mind is, when I am using the amp in A modes (since I do like the AC15/30 sounds very much), doesn't that mean that I run it in single-ended mode and consequently am wearing out one of the tubes sooner than the other? Would it make sense to swap them from time to time (of course with necessary biasing and testing)?

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Class-A can be single ended, but not necessarily. I tend to do single end Class-A in some of my own circuit designs.

When I want good dynamics and good linearity, I go to a double end mode, and have circuit that nulls any DC offsets.

It's more work, but the results are worth it for something beyond guitar amps that require top notch SNR and dynamic range.

 

Can't really say how we're doing it here. Between modeling and the analog amp sections, it will be a hybrid model.

 

I talk about it here somewhere, about how often tubes should be replaced, and that's dependent on play hours and how hard one plays.

 

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Hi there,

long time tube amp user, modeller user (currently Kemper , Atomic Amplifire, Boss GT 1000). Recently purchased a DT50 112 (currently in the shop getting repaired - refer "Whisper Quiet" thread).

 

For over twenty years, I have changed my own tubes and re-biased amps. I am a bit of a tube 'cork sniffer' and have my own tube testing gear and a fair supply of tubes of multiple brands.

 

I am not a tech and would always bow to Psarkassian's greater knowledge on this topic. However .....

 

My experience over time is that all tube brands (except maybe Mesa & Groove tubes) can vary significantly within classes, particularly the cheapies. 

 

I find it hard to believe that a fairly generic 'Chinese preamp' tube or Chinese manufactured EHX 6L6 could be the difference between an amp failing or working properly. (If this is the case, isn't this an amp design issue?).

 

Have these Chinese preamp tubes and EHX 6L6's been unwavering in their specifications and performance over the past 10 years - Based on my personal experience, this is not the case.

 

I could understand it if tube specifications or tolerances were published or if Line 6 tested, branded and sold 'recommended' tubes, but blind faith in fairly low budget tubes seems a long stretch.

 

Call me cynical, but it sounds like marketing hokum.

 

Cheers!

Paul

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leperclown,...

 

It has to do with the modeling and how it is treated by the tube section, and how the tube section

talks back to the processor board, as well as biasing correctly. Also using the correct soft/medium/ hard

is also essential. Because of modeling and the need to stay within performance parameters, specified

brand and type are necessary. These amps are very unforgiving of deviation and modifications.

 

Seen too many of these come across my bench because of that,...  blown amp and processor boards,

red plated tubes, fuses and the like. Not a pleasant sight.

 

Not hokum, just they way it was designed. If it were all analog, it would be different, like swapping out

tubes in Marshall's and Ampeg's, like we used to do in the 1970's. Since the 70's, I guess I really am an old guy.

 

These are a different animal, got to cuddle them under the chin a little different.

 

 

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Hey Psarkassian,

many thanks for the response. I absolutely get the points you make (and have previously made) about the link between the tube characteristics, biasing and the modelling. My point (poorly expressed) was that for this relationship to be optimised (or indeed not cause damage to the amp) then the characteristics/specs of the nominated tubes would have to hold absolutely constant across manufacturing batches over many years. It's the tube manufacturing quality and standards (Chinese 12AX7's & EHX 6L6's) that I am skeptical of.

 

I believe that the most optimal combination is a modelling preamp mated to a tube power amp + guitar cabs. I have previously had a SpiderValve 100 (MKii) and that got awfully close. I am hoping that the DT amp closes that gap even further.

 

Cheers & thanks!

Paul

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Yes, EH premium tubes go thru another set of tests for us. 

 

The Chinese 12AX7's are used in Spider Valve, though one can also EH low microphonics.

Even the Spider Valve, can't use a 6L6 because the characteristic curve isn't close enough to a 5881.

Bogner chose the 5881 because it was easy to design with, perform they way he wanted, easy

to get at good price. DT series is a bit more of a different side of Valve amps.

 

DT series amps are also more particular and finicky, because there are four topologies,

and so four gain loops, as well as the amp class switch.

 

Closing the gap,... Roland Orzabal (Tears For Fears) and Steve Howe (Yes, Asia, GTR) must think so,

as the both have two DT50-212's. Had the honor and pleasure of servicing all four amps.

 

 

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On 2/2/2021 at 3:09 PM, psarkissian said:

:)

Anytime, it's what I'm here for.

 Hey psark I'm gonna buy an extra set of tubes for my dt50 I don't have a line6 service center anywhere remotely close to me at all so I want to make sure I have the correct ones for the local amp guy in town when I do need them changed.  https://tubedepot.com/tubes_by_amp/DT50?utm_source=google&utm_medium=cpc&adpos=&scid=scplp361standard_tube_set&sc_intid=361standard_tube_set&gclid=CjwKCAjw07qDBhBxEiwA6pPbHi8N-8ElCCCJk4-AXRV8KXWy0qH2GyImsAX6cSChmOQEloOVhGoKghoCOv8QAvD_BwE

 

I was gonna order from here and they let you choose whether tubes you want however I noticed when I pick electharm12ax7eh and elctroharmEL34eh they don't have an option for medium....... Is that usually a spec I need to watch out for, or as long as I pick the eh tubes they are speced correctly?

 

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Yes, have to be mediums.

DO NOT use JJ's,... I have had problems with those in the past. Luv 'em,.... just NOT in these amps.

 

Because of the four topologies, there is a bias/burn-in procedure that MUST be done, and only a Line 6 service center can do that.

Also, your serial#, it needs to go into an authorized service center to check for a service bulletin. Need to make certain it's been done.

The amp depends on it.

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Do you know or have any suggestions for where to go? I live in knoxville tn ... And do they make the eh tubes in anything other than medium as long as I get the eh 12ax7eh and eh el34eh am I in the clear

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Noted looks like I have one about 3 hours away that isn't too bad....... But honestly I want everything to be done right..... I'd rather put in alittle extra to know I'm good for sure

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