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Dt25 Tube Upgrade: Quick Review Of Jj's Tube Upgrade


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#41 Tboneous

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Posted 20 March 2014 - 02:37 PM

the DT50 does not have preamp tubes...

it has an inverter 12ax7 like the dt25

and a boost 12ax7 which the dt25 does solid state...

all pre-amps are entirely modeled.

I sent my DT50 2X12 in for repairs. Here is how the support ticket went:

 

*Can you tell me what the hell was up with my DT?

 

*Hi,
Looks like the tubes were going bad. Normally there's just a 90-day warranty on the tubes, however we replaced the preamp and power tubes on your amp and rebiased them.

 

*Preamp tubes? What you talkin' 'bout Willis? There aren't any Preamp tubes. Right? or am I totally out to lunch?

 

*Hi, yes there are preamp tubes, they're the 12AX7's.

 

 

There seems to be a bit of a disconnect. This Line 6 person says that indeed, the DT50 has preamp tubes. You are saying that it doesn't.

 

I think a comparative diagram would be helpful. One of a "normal" tube amp and one of a DT amp.


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#42 TheRealZap

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Posted 20 March 2014 - 02:50 PM

I'm sure he was referring to them in a more generic sense. (much the same way a tissue is a kleenex and a swab is a qtip)

I'm 100% confident in my statement, having been told by the product manager himself in the DT beta.

as an IT guy, there are times when i have to dumb it down just to get a basic concept across. 

you never know who you're dealing with, perhaps he gave you the dumbed down version.

 

 

I sent my DT50 2X12 in for repairs. Here is how the support ticket went:

 

*Can you tell me what the hell was up with my DT?

 

*Hi,
Looks like the tubes were going bad. Normally there's just a 90-day warranty on the tubes, however we replaced the preamp and power tubes on your amp and rebiased them.

 

*Preamp tubes? What you talkin' 'bout Willis? There aren't any Preamp tubes. Right? or am I totally out to lunch?

 

*Hi, yes there are preamp tubes, they're the 12AX7's.

 

 

There seems to be a bit of a disconnect. This Line 6 person says that indeed, the DT50 has preamp tubes. You are saying that it doesn't.

 

I think a comparative diagram would be helpful. One of a "normal" tube amp and one of a DT amp.


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#43 Tboneous

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Posted 20 March 2014 - 03:31 PM

I'm sure he was referring to them in a more generic sense. (much the same way a tissue is a kleenex and a swab is a qtip)
I'm 100% confident in my statement, having been told by the product manager himself in the DT beta.
as an IT guy, there are times when i have to dumb it down just to get a basic concept across. 
you never know who you're dealing with, perhaps he gave you the dumbed down version.

Well that's just great! I get the dumbed down version of my wife's doctor stuff, I get the dumbed down version of my kids hockey stuff and now I'm gettin' it here! I specifically stated that i knew the DT didn't have preamp tubes and he still felt it needed to be dumbed down? He couldn't just say "you are right, i was referrigng to the 12AX7's? That's not dumbing it down, that's pretty close to a fib. That's just wrong man and is really confusing!
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#44 TheRealZap

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Posted 20 March 2014 - 03:34 PM

I was only theorizing. No idea why he said anything. Maybe he just doesn't know.
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#45 Tboneous

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Posted 21 March 2014 - 09:07 AM

I was only theorizing. No idea why he said anything. Maybe he just doesn't know.

I knew where you were coming from. But it is interesting that the DT literature referres to "preamp tubes"

"Switchable analog components.
Each Voicing can become a classic powerhouse or totally customized thanks to tube amp guru Reinhold Bogner’s uniquely flexible design. The (2) 12AX7 preamp and 50W, (2) EL34 power section offer easy reconfiguration of operating class (Class A/Class AB) and power tube mode (Pentode/Triode) for a wide range of feels and tones that can be added to each Voicing: modern or vintage, tight or dynamic."

"What configurations do the amps come in?

DT50 112
50W/25W
(2) 12AX7 preamp tubes, (2) EL34 power tubes
1x12" Celestion® G12H90 speaker
DT50 212
50W/25W
(2) 12AX7 preamp tubes, (2) EL34 power tubes
1x12" Celestion® G12H90 speaker
1x12" Celestion® Vintage 30 speaker
DT50 Head
50W/25W
(2) 12AX7 preamp tubes, (2) EL34 power tubes"

And the spec page clearly talks about 12ax7 preamp tubes.

You have never given be bad info so I believe what you are saying, but you can see why there may be some confusion on this one.

Hey line 6, maybe you could do a walk through video about this pre amp thing. It would be great to get clear understanding of how this amp works.
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#46 TheRealZap

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Posted 21 March 2014 - 09:15 AM

perhaps 12ax7's are just always reffered to as preamp tubes, as that is their typical use or reason for being.

and perhaps my info only refers to what the tubes actually do. they may do those things within the confines of the preamp section.

just saying it's possible we are both right to some degree. i know what we call the pre-amp from a tone perspective is the digital model.


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#47 Tboneous

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Posted 21 March 2014 - 07:12 PM

Can you explain what the 12ax7's do  in the DT's that is different than what they do in a "traditional" valve amp?


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#48 radatats

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Posted 21 March 2014 - 07:29 PM

they are not gain stages as found in a normal tube preamp.  The DT25 and the 50 each use a 12ax7 as a phase inverter for the power tubes.  This is a standard configuration for a tube power section.  My all tube Crate has 4 12ax7s, 3 for gain stages in the preamp and 1 as phase inverter for the power tubes.   The DT50 has a second 12ax7 which is technically a gain stage but not in the traditional preamp sense.  It is used as a Boost when selected to add a little more juice to the signal feeding the power tubes but it is still not part of the preamp section (it has no tone shaping function).

 

I hope this makes sense...  :blink:

 

For better understanding try this link...  http://www.300guitar...phase-inverter/


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#49 boyce89976

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Posted 21 March 2014 - 07:31 PM

Can you explain what the 12ax7's do  in the DT's that is different than what they do in a "traditional" valve amp?

 

It performs the same function as in any other amp, only it's limited to the Phase Inverter position in the DT (at least in the 25, and likely the DT50 too).  The PI is the last tube before the power section, and could be included in what is normally called the "preamp" stage.   


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#50 radatats

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Posted 21 March 2014 - 07:45 PM

It performs  The PI is the last tube before the power section, and could be included in what is normally called the "preamp" stage.   

 

That is quite possibly exactly what the tech meant by calling it a preamp tube...  Its function is to split and mirror the signal and apply equal but opposite to each power tube so yes, you could call it the final part of the preamp...

 

This is confusing to the average player though who associates preamp tubes with gain staging and tone shaping...


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#51 Tboneous

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Posted 21 March 2014 - 10:35 PM

i think i understand. thanx for the lesson. A bit confusing but I can feel the fog starting to lift.


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#52 Brazzy

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Posted 22 March 2014 - 06:41 AM

i think i understand. thanx for the lesson. A bit confusing but I can feel the fog starting to lift.

 

I was reading the old forum when it was new and a conversation came up about this with Nick Mattocks so even before I bought a DT I knew about the preamp tubes. This must be one of those areas where Line 6 played with the guts to make the DT beast what it is. I like it though.

 

P.S.: I had some tube noise yesterday, after warming up the DT50 clicked the Standby to start playing and got some fizzly, crackly sound momentarily so I clicked the standby on for a few seconds and then clicked it back off and all was fine, played for 1.5 hrs. with good tone in Top II, Pent 50w mode. I suppose that took some life from the tubes (originals since Nov 2013).


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#53 MAP70

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Posted 22 March 2014 - 06:56 PM

Which tube is the inverter tube in the DT50 1x12?? I am going to be changing the 2 12ax7's... if looking from the back of the amp, which is the inverter??

 

Thanks!

 

Mark


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#54 boyce89976

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Posted 22 March 2014 - 08:02 PM

Which tube is the inverter tube in the DT50 1x12?? I am going to be changing the 2 12ax7's... if looking from the back of the amp, which is the inverter??

 

Thanks!

 

Mark

 

The 12AX7 closest to the power tubes is always the PI.  


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#55 MAP70

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Posted 23 March 2014 - 04:38 AM

Great Thanks!!

 

Mark


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#56 MAP70

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Posted 23 March 2014 - 04:46 AM

Well they both seem to be next to the power tubes they are side by side behind the power tubes...looking at the amp from the back right side up is it the left or right 12ax7?


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#57 MAP70

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Posted 23 March 2014 - 05:10 AM

Looks like I fond it here....http://line6.com/sup...ew/thread/64496


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#58 Lawless33

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Posted 26 March 2014 - 10:13 AM

I work with a guy who swears he never rebiases his tube amps.  I told him I was going to have the original tubes swapped out of my DT25 combo for some new JJ tubes and he believes it shouldn't need re-biased.  I'd be afraid I'd fry something if I didn't have that done, as I'm a complete newb with that stuff.

Any thoughts?

Wes


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#59 TheRealZap

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Posted 26 March 2014 - 10:28 AM

that works with preamp tubes....

maybe he gets lucky.... or likes the difference with cold/hot tubes... 

i personally wouldn't do this, or recommend that you do.

 

I work with a guy who swears he never rebiases his tube amps.  I told him I was going to have the original tubes swapped out of my DT25 combo for some new JJ tubes and he believes it shouldn't need re-biased.  I'd be afraid I'd fry something if I didn't have that done, as I'm a complete newb with that stuff.

Any thoughts?

Wes


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#60 Lawless33

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Posted 26 March 2014 - 12:07 PM

Thanks, Zap!


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