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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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