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cyberspeedjunky

Pre-Amp Tubes

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Can anyone help me please? 

 

I noticed that when my DT50 212 heats up like after an hour of practice I lose distortion/gain if I crank it up, I wondered if I have blown a tube so I took a look through the back and my power tubes are lit up but my preamp tubes (which are located behind the power tubes) aren't.

does that mean they have blown?

 

I am assuming so but this my first tube amp so I am in unfamiliar territory learning as I go and I desperately need to find out if I need to replace them or not so I can sort out the problem and get back to jamming.

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Can anyone help me please? 

 

I noticed that when my DT50 212 heats up like after an hour of practice I lose distortion/gain if I crank it up, I wondered if I have blown a tube so I took a look through the back and my power tubes are lit up but my preamp tubes (which are located behind the power tubes) aren't.

does that mean they have blown?

 

I am assuming so but this my first tube amp so I am in unfamiliar territory learning as I go and I desperately need to find out if I need to replace them or not so I can sort out the problem and get back to jamming.

I'm not an expert, but I doubt there's a problem with your 12AX7's.  Those aren't actually providing any gain or distortion--that's all done digitally.  Your power tubes might be aging, though.  

 

There's mixed opinion on this, but I have a cooling fan pointed at the back of my DT50-112 because it just seemed to be getting too hot.  Might be worth a shot?  

 

Hang in there and I'm sure more definitive answers will arrive.  There are some genius amp gurus in this forum who no doubt will soon impart more technical knowledge than I can.

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Thanks for your suggestion and encouragement, I will get a fan for my amp actually it does seem to feel really hot if I crank it up and play for a couple of hrs., could I ask you a question? you ever had to replace your tubes?

 

I was doing some research on tubes in case I need to replace them at any stage in the future and discovered that there are loads of different brands at varying prices, top of the line on one site was priced at $119.00 each for preamp tubes I was wondering if they are like pc components - you get what you pay for?

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Thanks for your suggestion and encouragement, I will get a fan for my amp actually it does seem to feel really hot if I crank it up and play for a couple of hrs., could I ask you a question? you ever had to replace your tubes?

 

I was doing some research on tubes in case I need to replace them at any stage in the future and discovered that there are loads of different brands at varying prices, top of the line on one site was priced at $119.00 each for preamp tubes I was wondering if they are like pc components - you get what you pay for?

 

There are *extensive* threads on the subject of tube choice. I don't know enough on the technical specifics; but I know a Line6 employee weighed in on those threads, and specifically said "Only Use EH Tubes"....

 

For what it's worth, I had put JJ's in my two DT25's, then shortly after ended up swapping them back out for EH tubes.. I felt like an idiot, but didn't want to risk non-EH tubes causing me problems. Though, the 12AX7 does something different on the DT25 than it does on the DT50; I think the two (stock) 12AX7 tubes in the DT50's are also EH brand; they use some Chinese tubes for the single 12AX7 in the DT25.

 

http://line6.com/support/topic/2998-is-it-a-tube-problem/?hl=tubes&do=findComment&comment=83528

http://line6.com/support/topic/12006-dt-tubes-is-there-only-one-choice/?hl=tubes

 

response from Partev Sarkissian (Line6 tech):

 

Sent 13 February 2015 - 10:33 AM

Because of the way Bogner designs the tube portions of these amps,

and that this is a hybrid and not the usual bill-of-fare tube amp, you should

re-tube using the specified EH from Electro-Harmonix tubes.

 

You can't use the EH bias spec on other tubes. The spec is dialed in for

the EH's. All too often these come across our bench for no other reason

than having non-specified tube inside (JJ's, Mesa, Groove Tube), using the

specified bias. That does not work.

 

They (JJ's, Mesa, Groove Tube) would have to be bias slightly different,

because the characteristic curves from one to the other are not exact. That

little of difference, makes all the difference. I've seen too many blown amps

just because of that. It's a hybrid and a hot rod, don't mess with it.

 

Stick with the specified EH's.

 

Partev Sarkissian

Repair Technician, Repair Dept

Line 6, Inc.

26664 Agoura Rd

Calabasas, CA 91302

phone: 818-575-3600

web: www.line6.com

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Thanks for your suggestion and encouragement, I will get a fan for my amp actually it does seem to feel really hot if I crank it up and play for a couple of hrs., could I ask you a question? you ever had to replace your tubes?

 

I was doing some research on tubes in case I need to replace them at any stage in the future and discovered that there are loads of different brands at varying prices, top of the line on one site was priced at $119.00 each for preamp tubes I was wondering if they are like pc components - you get what you pay for?

 

Tubes can last anywhere from 3-6 months to several years.  The more volume and distortion, the more hours per week, the faster they go.

 

I bought my DT50-112 in February (used), and suspected that the tubes might need to be replaced so I bought a new set.  It turns out the tubes it came with are fine, but it doesn't hurt to have a 2nd set.

 

I would NOT say that you get what you pay for with tubes.  It's really more of a personal taste thing for some guitarists.  You MUST only use the Electro Harmonics (EH) tubes for the power tubes, and these must be biased to 36mv if you replace them (a matched set is required).  If you use other power tubes, then the bias setting is no longer valid, and if you don't know what you're doing you might have a meltdown on your hands.  Actually, if you don't know how to bias your amp you'd best take it to a pro because the high voltages in the amp can kill.  A matched pair of EH EL34's is $32-$40.  Your tech can sell them to you and bias them at the same time.

 

For the 12AX7's you can use any brand, and there's nothing to bias so you can swap these yourself.  I'm thinking of testing out a Mesa tube for the inverter position to see how I like it.  There's another thread in here where Spaceatl says which specific tube he's using--it's a balanced inverter so it's technically not a 12AX7.  (He is also not using the EH power tubes, but he's a guru, unlike us).

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Thank you for the info I played acoustic most of my life I've only been playing electric for about 2 years and my DT50 212 is my first tube amp. thank you for the specific info on the tubes I appreciate the support thanks! 

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Thanks for the support greatly appreciated, I am still learning about my DT50.

 

Just wondering if your amp still does that.  Yesterday I noticed that my dt50-112, after more than an hour of playing, wasn't giving me the same sustain.  Lack of distortion too, but I mostly noticed the lack of sustain.  I thought it might be the guitar strings or something, but then this morning I remembered your post, so I'm wondering if there's a connection.  I'm going to see if it happens again today, and spend more time on the symptoms if it does.

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I gotta say both my DT50's start to sound better after 30 minutes or so.  Either that or my ears get more forgiving.  I have the stock pre-amp tubes but have Svetlana E34L power tubes.  They were installed by a pro tech and have been in heavy use for about a year, no problems.

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yes still having this problem I setup channel 'A' on the 'American Clean' voicing settings and run my distortion pedal on - on my pedal board with the Master Volume knob turned up to about a quarter way I get plenty of sustain and distortion for about an hour too but when I crank it up to halfway to play with a backing track it goes clean on me with less sustain very frustrating.

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yes still having this problem I setup channel 'A' on the 'American Clean' voicing settings and run my distortion pedal on - on my pedal board with the Master Volume knob turned up to about a quarter way I get plenty of sustain and distortion for about an hour too but when I crank it up to halfway to play with a backing track it goes clean on me with less sustain very frustrating.

Is it possible it's your pedal board? Just kinda thinking out loud here. I don't use pedals anymore, just my HD500. Are you plugged into the Hi or the regular input jack? You might try switching just to see?

 

I'm stumped now. Saturday I started fiddling with the triode switch and class A--before it was always pentode and class AB. I was also exploring the differences between low power mode and regular. I went direct in and then via my POD and the L6 link. I was getting amazing tones anyway I set it, and was thinking I should buy more line 6 product. then after 90 minutes or so I started losing the sustain. I called it quits. Then yesterday I couldn't get a good tone for the life of me. Everything was all fizzy. Now wondering if it's LP Mode, tubes, or what? so frustrating!

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yes still having this problem I setup channel 'A' on the 'American Clean' voicing settings and run my distortion pedal on - on my pedal board with the Master Volume knob turned up to about a quarter way I get plenty of sustain and distortion for about an hour too but when I crank it up to halfway to play with a backing track it goes clean on me with less sustain very frustrating.

 

Okay, 2 days of playing and analyzing hence, and I'm unable to reproduce or experience either the sustain drop-off or that fizzy bummer.  Instead, I'm getting tones I want (or at least I'm getting what I'm asking for).  So I dunno--was what I was hearing me?  Was it my ear failing, or me building crappy patches that sound good with a backing track but lousy when isolated?  Or is there something intermittently wrong here?  I'm leaning toward the conclusion that all is as it's should be.

 

Part of that is because I've decided "to hell with my neighbors" and have opened up the volume a tad to get closer to the amp's sweet spot.  And one other thing I found--that I didn't know until this week--is that switching to "triode" reduces the noise.  It also reduces power by 50%.  I've found that this helps with some tones.  In triode function you lose attack, headroom, power, and the amp seems less lively.  But for crunchy tones at a lower volume, it seems to dramatically reduce any fizzies, it allows for more sustain and saturation, and it even mellows my lower string riffs and stuff while somehow making them stand out better.  (kinda like changing the laws of physics, that.)  So I'm thinking I'll go pentode for voice 1 and triode for most patches using voices 2-4.  When I play with drums, I'll probably go pentode for all, but for practicing I believe this is my ticket.

 

Another surprise was that low power mode can really alter how the gain setting interacts with the tone.  I was in voice 1 with LPM off and the gain up to 2:00, and I turned LPM on and all of a sudden I got crunch and saturation (after turning up the master, natch).  It was like going from the Bassman amp to Dr Z by simply pulling out the knob and turning up the volume to reach the same loudness.  That's huge to me, because it tells me that there are essentially 2 different amps for every amp, I just need to figure out when to switch power modes.  Unfortunately, this can't be saved to a patch--an option that as of today I'd really love!

 

Well, cyberspeedjunky, I hope you can solve your problem.  Maybe some of this stuff I threw out there helps?  If you uncover any more details, I encourage you to post them because the forum users are a helpful bunch, and resolutions (if not actual solutions) are often found here.  Some easier than others, though.

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