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Is It A Tube Problem?


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#1 cw0401

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Posted 01 October 2013 - 01:11 AM

Hi.

Every time I try to use external analog OD pedals with the DT, it get a high pitched whine at the same time as the pedal sound. The higher the gain the woes it gets.

Doesn't make any difference changing the cables or which pedal is used but it is worse on higher gain pedals. It is there whether going direct such as JTV59 - OD - DT25 or JTV59 - OD pedals - POD500 - L6 Link.

Changing the voicings on the DT again makes it worse the higher the gain.

Interestingly, when I just use the Dream Rig with no OD Analog pedals, there is no problem.

Could it be the tubes?

Thanks for any help.
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#2 shaker

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Posted 01 October 2013 - 03:04 AM

Could be the power supply to the OD causing it to whine, can you run it on a battery or another power supply to see if this alleviates the problem?


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#3 psarkissian

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Posted 01 October 2013 - 07:46 AM

Does it sound like a fax machine over a phone line, or a whistling kind of whine?


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#4 cw0401

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Posted 04 October 2013 - 02:18 AM

Does it sound like a fax machine over a phone line, or a whistling kind of whine?



Ummmmm.....more of a whistling whine perhaps like a TV when theres only the test pattern on or perhaps the sound of a hearing testing machine if you know what I mean.

I put my ODs on separate power cords instead of daisy chain and it was slightly better but still there on higher level gain
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#5 psarkissian

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Posted 04 October 2013 - 07:48 AM

Could be a slight ring,... do you use a high level of Reverb? Noise floor and a lot of Reverb, at high amplitude can do this.

 

Could be a tube going microphonic at high gains. The tubes in the DT Series of amps are chosen to be "low microphonic",

so that this won't happen. But maybe one is on the edge.

 

 


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#6 cw0401

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Posted 05 October 2013 - 01:16 AM

Could be a slight ring,... do you use a high level of Reverb? Noise floor and a lot of Reverb, at high amplitude can do this.

 

Could be a tube going microphonic at high gains. The tubes in the DT Series of amps are chosen to be "low microphonic",

so that this won't happen. But maybe one is on the edge.

No I wouldn't say I use a lot of reverb.  I like having some but not a great deal from the POD HD500.   With reverb in the amp, I just use the settings that are listed on the bit of cardboard on the top that comes with it.   Mainly use the British Crunch or Class A Chime.

 

I do have replacement tubes but I might try to test the old ones first before bunging them in.

 

Thanks for the advice


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#7 psarkissian

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Posted 07 October 2013 - 08:34 AM

Be sure that these tubes are Line 6 authorized Electro-Harmonix power tubes (and the pre-amp tubes as well),

and that the power tubes are matched pairs.

 

Have a Line 6 authorized service center install them, they will have to be properly biased and the unit signal tested.

There is a proper biased and signal test that always has to be done on a tube amp, it's not a swap-n-play sort of thing.

Incorrect bias leads to distortions, distortions lead to stressed tubes, stressed tubes lead to a failing amp and a trip

to a service tech.

 

The Electro-Harmonix power tubes are scrutinized more so for Line 6, than what you would get from a store.

 

These are Bogner designed tube amp stages and not very forgiving with anything other than the specified tube brand,

so don't try to hot rod these hot rods with Mesa or Groove Tube versions.

 

The characteristic curves of the Mesa or Groove Tube versions are different enough to make a difference in performance

and can stress the amp. After which, at that point, it might end up on my bench, or one of my lab mate's benches,... and we

don't want that, we want it to run well for you.

 

Depending on how much you play, a tube swap (the amp equivalent of a car tune-up and oil change) should be done

every 12 to 18 months if you're a gigging musician,... every 24-months if you play less.

 

Take good care of the amp and it will take care of you. Always take it to Line 6 authorized service center for checking out

and servicing.

 

In the meantime, lock-n-load the rock-n-roll!


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#8 stumblinman

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Posted 07 October 2013 - 08:57 AM

Be sure that these tubes are Line 6 authorized Electro-Harmonix power tubes (and the pre-amp tubes as well),
and that the power tubes are matched pairs.

Have a Line 6 authorized service center install them, they will have to be properly biased and the unit signal tested.
There is a proper biased and signal test that always has to be done on a tube amp, it's not a swap-n-play sort of thing.
Incorrect bias leads to distortions, distortions lead to stressed tubes, stressed tubes lead to a failing amp and a trip
to a service tech.

The Electro-Harmonix power tubes are scrutinized more so for Line 6, than what you would get from a store.

These are Bogner designed tube amp stages and not very forgiving with anything other than the specified tube brand,
so don't try to hot rod these hot rods with Mesa or Groove Tube versions.

The characteristic curves of the Mesa or Groove Tube versions are different enough to make a difference in performance
and can stress the amp. After which, at that point, it might end up on my bench, or one of my lab mate's benches,... and we
don't want that, we want it to run well for you.

Depending on how much you play, a tube swap (the amp equivalent of a car tune-up and oil change) should be done
every 12 to 18 months if you're a gigging musician,... every 24-months if you play less.

Take good care of the amp and it will take care of you. Always take it to Line 6 authorized service center for checking out
and servicing.

In the meantime, lock-n-load the rock-n-roll!


Holy crap, an actual Line 6 employee?
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#9 psarkissian

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Posted 07 October 2013 - 12:51 PM

Shhh,... don't let get around.

 

And I'm a forum moderator. Trolling the forums is okay with my bosses,

so long as it doesn't take too much time away from me fixing stuff. A two

cents here, a two cents there,...

 

... oh, and being a moderator, maybe c#%*p would be a more netiquette way of saying it,

though it's probably okay here for now. I typically use "holy moly" or "mola mola". ;)

 

Rock on!


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#10 geppert

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Posted 07 October 2013 - 01:25 PM

Shhh,... don't let get around.

 

 

You participation here is greatly appreciated.

 

Now .... I want to do some mods on my DT25 (tech humour) ...


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#11 psarkissian

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Posted 07 October 2013 - 01:31 PM

I grok.   :)


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#12 geppert

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Posted 07 October 2013 - 01:43 PM

I grok.   :)

 

Ah good ... we grok each other ... this is a good beginning ....


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#13 stumblinman

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Posted 08 October 2013 - 07:13 AM

Shhh,... don't let get around.

And I'm a forum moderator. Trolling the forums is okay with my bosses,
so long as it doesn't take too much time away from me fixing stuff. A two
cents here, a two cents there,...

... oh, and being a moderator, maybe c#%*p would be a more netiquette way of saying it,
though it's probably okay here for now. It typically use "holy moly" or "mola mola". ;)

Rock on!


I figured crap was ok since it didn't get changed to lollipop.
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#14 toneman2121

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Posted 08 October 2013 - 04:16 PM

Be sure that these tubes are Line 6 authorized Electro-Harmonix power tubes (and the pre-amp tubes as well),

 

why?


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I'M SO HAPPY!


#15 stumblinman

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Posted 09 October 2013 - 08:04 AM

Be sure that these tubes are Line 6 authorized Electro-Harmonix power tubes (and the pre-amp tubes as well),

why?


Because L6 must get a cut of them or something. EH tubes are about my last resort.
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#16 psarkissian

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Posted 09 October 2013 - 08:49 AM

No extra cut that I'm aware of.

 

The Electro-Harmonix (EH) power tubes get extra scrutiny for Line 6, than what you would get from a store,

as far as I'm aware. Had a chat with Mike Matthews (the founder/owner of EH) about their tubes at NAMM

earlier this year.

 

EH bought a tube factory in Russia, it's theirs, they scrutinize the tubes really well. From others there can

be inconsistent batches of tubes.

 

Some of these inconsistencies go to the characteristic curves on the data spec sheets. These differences

can have an effect on performance or lifespan of the tube, as does correct biasing of the tube. And it's

even more crucial when it comes to Matched Pairs.

 

I know people like to use tubes versions from other tube companies in Line 6 amps. Not a good idea. I see

too many come back for problems, with these other tubes inside.

 

These other tubes are fine,... just don't put them in Line 6 tube amps. Bogner designed the tube stages of

our amps to use what we use, biased to what they're biased to,.... and these amps are not forgiving of

alterations, deviations or modifications.

 

It's like trying to over hot rod a hot rod, give it too much and you throw a rod or blow an engine,... and that's

never a pretty sight.

 

We recommend coming to us for tubes for Line 6, Bogner designed Spider Valve, Alchemist and DT Series

tube amps because, we can't vouch for other tube sources. Besides,... we have a 90 day warranty on our

tubes when you go to an authorized service center for amp servicing our tube amps.

 

 

Enjoy the tube sound. Rock-On!


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#17 daddydoodles

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Posted 14 October 2013 - 10:12 AM

I too have a HD500 running into a DT25. Intermittantly, there will suddenly be NO sound except a low volume high pitched squeal. The only way to resolve it to shut the amp off and turn it back on (presumably rebooting the amp). This is unacceptable since I might be playing along live and suddenly have no sound. Advice? Suggestions? I have only had the amp about 4 months. I have retubed it thinking that it might fix the problem. It does it even with the new tubes.


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#18 psarkissian

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Posted 15 October 2013 - 07:16 AM

Microphonics in the tubes,... but since you've swapped them out, that's not the case.

 

Digital clock bleeding into the audio from either the HD500 or the DT25 digital board.

 

Are you using the Line6 Link?

If so, are you using "Link 6 Link Cable" or a standard XLR mic cable?

 

 


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#19 mtreehugger

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Posted 12 February 2015 - 04:30 PM

No extra cut that I'm aware of.

 

The Electro-Harmonix (EH) power tubes get extra scrutiny for Line 6, than what you would get from a store,

as far as I'm aware. Had a chat with Mike Matthews (the founder/owner of EH) about their tubes at NAMM

earlier this year.

 

EH bought a tube factory in Russia, it's theirs, they scrutinize the tubes really well. From others there can

be inconsistent batches of tubes.

 

Some of these inconsistencies go to the characteristic curves on the data spec sheets. These differences

can have an effect on performance or lifespan of the tube, as does correct biasing of the tube. And it's

even more crucial when it comes to Matched Pairs.

 

I know people like to use tubes versions from other tube companies in Line 6 amps. Not a good idea. I see

too many come back for problems, with these other tubes inside.

 

These other tubes are fine,... just don't put them in Line 6 tube amps. Bogner designed the tube stages of

our amps to use what we use, biased to what they're biased to,.... and these amps are not forgiving of

alterations, deviations or modifications.

 

It's like trying to over hot rod a hot rod, give it too much and you throw a rod or blow an engine,... and that's

never a pretty sight.

 

We recommend coming to us for tubes for Line 6, Bogner designed Spider Valve, Alchemist and DT Series

tube amps because, we can't vouch for other tube sources. Besides,... we have a 90 day warranty on our

tubes when you go to an authorized service center for amp servicing our tube amps.

 

 

Enjoy the tube sound. Rock-On!

 

Question:  you're talking about the DT50 only, right?  DT25 ships with Sovtek power tubes, correct?  Can you tell me which of the available 3 "flavors" that the Electro-Harmonix EL34 tubes come in--soft, medium, and hard--are shipped in the DT50?  Can we use any of these 3 choices, or are we limited, and to which "flavor?"

 

THANKS!


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#20 ColonelForbin

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Posted 13 February 2015 - 06:56 AM

+1 to some clarification for the guidelines on tube options for us DT25'ers~!

As in, cool to use JJ's?


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#21 psarkissian

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Posted 13 February 2015 - 08:40 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 DT amp

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

come across my bench just because of that. It's a hybrid and a hot rod,...

best don't mess with it.

 

Stick with the specified EH's. 


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#22 psarkissian

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Posted 13 February 2015 - 08:46 AM

BTW,... EH owns the factory in Russia.


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#23 mtreehugger

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Posted 13 February 2015 - 09:53 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 DT amp

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

come across my bench just because of that. It's a hybrid and a hot rod,...

best don't mess with it.

 

Stick with the specified EH's. 

Thanks for the prompt reply!

 

There is a Q&A in the Knowledge Base by Line 6 Tony (http://line6.com/sup...50dt25-faq-r144) where he says that the DT25 ships from the factory with Sovtek, not EH, power tubes.  Another owner, inovine, reports that his DT25 was originally equipped with EH Tubes. (http://line6.com/support/topic/12006-dt-tubes-is-there-only-one-choice/)  Your assertion that only EH tubes can be used, does that pertain only to the DT50, or are you referring to both DT50 and DT25?  (Did Tony make a boo boo?)

 

Also, the EH EL34 comes in soft, medium, and hard matched pairs, with soft saturating the earliest, hard the latest, etc.  From your perspective, are these 3 "flavors" essentially the same thing?  Do they all meet spec, or is only one flavor recommended?  If so, which?  Finally, do you know which flavor ships from the factory?  (I would assume medium, but we all know what happens when one assumes, as is evidenced when we phonetically dissect the word into its components for analysis...)

 

: )

 

THANKS!!!!


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#24 psarkissian

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Posted 13 February 2015 - 11:18 AM

Flavors never mattered to me. some people are into that.

 

What we get from EH (matched pairs) has been extra tested saying that

they passed our requirements. They also have the crucial Plate Current

and Transconductance marked on them. What flavor they are, I don't

recall, they are what they are, fitted spec'ed for this group of amps. They

all meet the spec.

 

Mike Matthews of EH is an old school circuit geek (like me), so we always have

much to talk about when I see him at trade shows. As well as my trade show

chats with Aspen Pittman of Groove Tubes.

 

Tony, boo boo? Not really.

Sovtek, EH,...  same factory, and the factory is owned by EH.

EH marked tubes go through extra scrutiny.


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#25 psarkissian

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Posted 13 February 2015 - 11:28 AM

DT series likes EH's, never seen any China tubes in them from the factory.

 

Spider Valve uses 12AX7B (China) for preamps and Sovtek 5881WXT,...

should use the WXT versions especially a must if the tube retainers are

the "bear trap" type.

 

Alchemist amps are another story altogether and specified tubes are even

more crucial and specific.

 

These are hybrid amps with some complex gain loops, so using specified

tubes is a must.

 


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#26 mtreehugger

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Posted 13 February 2015 - 11:54 AM

Flavors never mattered to me. some people are into that.

 

What we get from EH (matched pairs) has been extra tested saying that

they passed our requirements. They also have the crucial Plate Current

and Transconductance marked on them. What flavor they are, I don't

recall, they are what they are, fitted spec'ed for this group of amps. They

all meet the spec.

 

Mike Matthews of EH is an old school circuit geek (like me), so we always have

much to talk about when I see him at trade shows. As well as my trade show

chats with Aspen Pittman of Groove Tubes.

 

Tony, boo boo? Not really.

Sovtek, EH,...  same factory, and the factory is owned by EH.

EH marked tubes go through extra scrutiny.

You almost make it sound as though the EH EL34 pair I ordered from MF would not meet the same requirements that the OEM tubes meet.  That can't possibly be, can it?


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#27 psarkissian

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Posted 13 February 2015 - 12:08 PM

"You almost make it sound as though the EH EL34 pair I ordered from MF

would not meet the same requirements that the OEM tubes meet"---

 

I guess the operative word is "almost".

EH matched pairs should have a spec marked on it (Plate Current and Transconductance).

If it's EH and they're matched they would fine. From MF or whoever has them is fine.


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#28 ColonelForbin

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Posted 13 February 2015 - 02:28 PM

Well, I will be worried now every time I use my DT25! Oh well, I am the guinea pig experiment; I guess I should have read more before I took my amps to get retubed. 

 

I can confirm that both of my DT25's had Electro-Harmonix EL84's, and 'Chinese' 12AX7B. (they just say China on them, no brand indicated)

 

I will save the EH tubes for just in case, but if the JJ's give me any problems, I will probably redo the whole process... 


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#29 mtreehugger

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Posted 13 February 2015 - 04:03 PM

Well, I will be worried now every time I use my DT25! Oh well, I am the guinea pig experiment; I guess I should have read more before I took my amps to get retubed. 

 

I can confirm that both of my DT25's had Electro-Harmonix EL84's, and 'Chinese' 12AX7B. (they just say China on them, no brand indicated)

 

I will save the EH tubes for just in case, but if the JJ's give me any problems, I will probably redo the whole process... 

 

i think some have had success with the jj's.  

 

i spose the operative insight here from l6 psarkissian is "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 DT amp specified bias. That does not work."

 

notice that he doesn't say "never," he says the EH spec doesn't work for other tubes.  (he strictly non-recommends other tubes in general too, as a general rule...) From another post in an other thread, spaceatl said that the proper way to bias is with a signal generator and an ocilloscope, adjusting the bias to remove the "notch" you see on the scope.  if i were you, i'd verify that your tech did this, and ask him what the bias voltage he arrived at was.  if he didn't do this, i.e. if he merely set the bias to the spec given by line 6 for eh tubes only, and all he used was a voltmeter, then he didn't do your tube install properly, and you could very well just give him back the tubes and refuse to pay.  if you supplied the tubes, refuse to pay and take it somewhere else.

 

well, that's my 2 cents after taking all of this in.  okay, i'm not a guitar amp service tech, but i did graduate top of my class at electronics school and learned gobs of junk that i still kinda remember.


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#30 mtreehugger

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Posted 13 February 2015 - 04:04 PM

"You almost make it sound as though the EH EL34 pair I ordered from MF

would not meet the same requirements that the OEM tubes meet"---

 

I guess the operative word is "almost".

EH matched pairs should have a spec marked on it (Plate Current and Transconductance).

If it's EH and they're matched they would fine. From MF or whoever has them is fine.

 

Thank you so much for unraveling this mystery for us!!!


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#31 spaceatl

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Posted 13 February 2015 - 05:34 PM

I guess I will say something since I got called out here...Please keep in mind that what I post on these boards is my opinion based on my own experience. I have been working on and using tube amps for little while and I have my own strong opinons and know what I like and how I like my amps to operate...I have been using Mesa tubes in my DT50 for about 4 years now...same thing in my DT-25....I do use a GTSAGAX7 for my inverter...I have had no issues, my amps have lower noisefloors than they did with the stock tubes and sound fantastic...Same with my SVMK1 and SVMK2...anyhoo...take that with a grain of salt...what works for me, may not work for you...

 

Here is a really great article written by Randall Smith that really explains fixed bias tube amps in a way that most people can understand...Back when tube amps were common, this is how you designed them...Fixed bias means fixed bias...adjustment is needed now because we just cannot get tubes as well matched as they were 40 years ago when you could trace test your tubes at the local drug store...

 

http://mesaboogie.co...rk1 Reissue.pdf

 

He does have some very strong opinions, but it still a good read...Here's link to the Mark 1 Re-issue manual (The article is at the back of the manual)....copied below.

 

Bias Adjustment - Randall Smith

 

Here’s a question we often hear: “Why doesn’t Mesa put bias adjustments in their amplifiers?”

 

Well, there’s a short answer and a long answer to this question. The short answer is that during my 12 years of repairing Fenders, one of the most frequent problems I saw was bias controls that were either set wrong or that had wandered out of adjustment due to vibration. As any honest tech will tell you, there’s lot’s of easy money to be made by sprinkling “holy water” on amplifiers ... uh, what I meant to say is “Your amp needed biasing.” See what I mean? What customer is going to argue with that? It only takes a moment and a volt meter: The Fender diagram shows how: “Adjust this trim pot for - 52 volts.” That’s it. Nothing more. Now don’t be fooled into thinking that tubes “draw” more or less bias, they don’t. The way a bias supply is connected to a tube is akin to a dead end road, it just trails off to nowhere without really completing a circuit. It’s a static voltage and regardless of what tube is in the socket — or even if the tubes aren’t plugged in at all, it doesn’t change the bias voltage a bit. So the end of the short answer is this: Since a bias supply needs to put out the right voltage and never vary, I wanted to build amplifiers that were individually hard wired to the correct values and NEVER needed adjustment. And for 25 years, that’s how Mesa/ Boogies have been built. Time to change tubes? Just plug our tubes into any one of our amps and you’re DONE. No tech needed. NO bills and no BS about biasing. And most important: The bias is RIGHT because it can’t change! Now, you want the long answer? Here’s more information on how our hard-wired bias avoids trouble. Please read on. But first, let’s make an important distinction. Our business is designing and building high performance amplifiers. And for this we need tubes whose variance is within a narrow range. Our warehouse is full of rejects ...oh, they work — they just don’t perform within our tolerance range. We have a very sophisticated computer - based tube testing system (nicknamed “Robotube”) that matches and measures tubes over seven important parameters. It can even predict which tubes are likely to have a shortened lifetime — even though they work perfectly during the test. Because our business is building quality amps, we can afford to reject a lot of wayward tubes. The guys you hear complaining because Boogies don’t have bias adjusters are primarily in the business of selling tubes - not amps. They don’t want to throw away 30 percent of their inventory, so they promote the idea that tubes outside our parameters can be used to “customize” amplifiers and they criticize us because our amps can’t be adjusted to accommodate their out-of-Mesa tolerance tubes. Now you might be thinking, “But I thought you just said that tubes don’t “draw” bias, therefore they don’t effect the bias supply and thus it doesn’t need to be adjustable.” And that’s right. Tubes don’t effect the bias setting, but the bias setting does effect how the tubes work. But how it effects the tubes is difficult to measure. . . . . . . . .. ... .... .. ... .. .. ... .. .. ... .. .. ... .. ( ) ( ) ( ) , ( , ) ( ) Structure of a 6L6 / 5881 Beam Power Pentode. PLATE BEAMCONFINING ELECTRODE SCREEN GRID GRID CATHODEPAGE 19 BIAS ADJUSTMENT: When you set the bias (whether it’s by selecting the right resistors, as we do, or adjusting a trimmer — which is quicker) what you are doing is establishing the correct amount of idle CURRENT that flows through the power tubes. But you can’t adjust the current directly, you can only change it by adjusting the amount of bias VOLTAGE that goes onto the tubes’ control grids. Voltage and current are NOT the same. Current is the AMOUNT of electricity, the “quantity” — and is measured in amperes. Voltage is the degree of electric charge — like the “pressure” to use the old water analogy. Let me illustrate how different voltage and current are: When you scrape your feet across a carpetted floor in dry, wintery conditions, your body can become charged with 50,000 to 100,000 volts of static electricity. And when you reach for the door knob, a spark jumps and you feel it! The voltage is super high but the current (measured in micro-amps) is tiny - otherwise you would die from electrocution. Contrast this with your car battery, which puts out a mere 12 volts. You can lay your hands right across the terminals and not feel a thing. Yet the amount of current available can run to several hundred amperes .. enough to turn over a cold engine and get it started. So current and voltage are two totally separate electrical parameters — though when you multiply them together, you get POWER, which is measured in watts. When you set the bias of an amplifier, you are adjusting the static VOLTAGE at the control grid of the tube in order to produce a desired amount of idle CURRENT flowing to the tube’s plate. A small change in grid voltage, produces a large change in the amount of current flowing — and that’s basically how a tube works. Say that again because it’s super important: A small change in voltage at the grid causes a large change in current flowing to the plate. See, that’s the essence of amplification: A small change causing a large change. And here it’s a small voltage change causing a large current change. The bias conditions are what determines how much current flows through the big power tubes when you’re not playing. And what drives your speakers is flucuations in that current flow when are ARE playing. If the amount of current increases and decreases 440 times per second, then you’ll hear an A note. If the fluctions in current flow are large and still at 440 per second, you’ll hear an A that is LOUD! But for purposes of biasing, it’s the amount of “plate current” flowing with no signal applied that’s important. Unfortunately current is hard to measure because the circuit must be interuppted — as in “cut the wire” — and the meter spliced “in series” with the broken circuit. But measuring VOLTAGE is easy. It is not necessary to interrupt the circuit because a voltage reading can be taken in PARALLEL with the circuit intact. Thus, as a matter of convenience, most bias settings are given in volts at the grid ... even though current through the plate is the important factor. In fact plate current is so inconvenient (and dangerous) to measure that Fender doesn’t even state what the correct value should be. They only give the grid voltage that will produce that current. (That’s the minus 52.) But that only happens if the tubes being used are “in spec.” As long as the tubes ARE “in spec”, the right bias voltage will always give the correct plate “CURRENT” — but then there’s no need for the bias voltage to be adjustable! If the tubes are NOT in spec, then the only proper way to re-set the bias is to cut the circuit and measure the current while adjusting the bias ... but no manufacturer I know even STATES the desired current value! Be that as it may, when the original bias voltage is altered far enough, it will compensate for the tube’s abnormal performance and the correct amount of idle current flow may then be restored. Clearly this is something most repair techs should not attempt. Some newer amps have LED indicators connected to the circuit which will turn on when the right threshold of current flow has been reached. This is an improvement, and almost worthy if you’re willing to except resistors and lights added into your amplifier’s audio path — which we aren’t. The other “advantage” of this system is that it allows some amp manufacturers to avoid matching their power tubes. The thinking is that adjusting the bias to each tube separately eradicates the inherent differences between the tubes by insuring that the same current flows through each one.PAGE 20 BIAS ADJUSTMENT: (Continued) Again, this has some merit .. but it’s still not as good as using tubes that are matched in the first place because compensating for the mis-match causes the push-pull circuit itself to become unbalanced. Two wrongs don’t really make a right. Some of the other recommended biasing, “methods” — such as -”.. tubes running red hot, increase the bias .. sounds harsh and runs too cool, turn it down ...” are guesswork at best. Luckily, one of the great things about tube amps is that they can usually stand some abuse without causing any real harm ... at least not immediately. But don’t these alterations imply that you are second-guessing the amp designer and that there’s a better set of operating conditions that the designer missed but the tube sellers have discovered? Now some players may like the sound of their amp altered by tubes with extreme characteristics and with the bias set to help compensate. But often it is the mere novelty of change that they’re really responding to and when the amp goes back to the proper original way, we’ve seen them be far happier still! Because every part in every one of our designs has been meticulously evaluated, compared and stressed over — no matter how seemingly insignificant it might be. And with every design we look for a “sweet spot” where all the parameters — including the bias — come together to give the best sonic performance, consistently and reliably. Every part and voltage is important — yet no one complains that these other parameters aren’t available for tinkering. Consider our patented Simul-Class circuitry where there are two different bias voltages used for separate pairs of power tubes ... and changing one voltage also changes the other. Great care goes into getting this just right and we think we’d be asking for trouble to have it adjustable for the world to play with ... unless you like paying to have your amp messed up. Sorry, I meant to say, “Uh, ... your amp needed biasing.” If that doesn’t appeal to you, then merely plug a matched set of Mesa tubes into one of our amps and you’re ready for tone. Guaranteed. You’d be amazed at the number of service calls we field every day that lead to a diagnosis of out-of-tolerance, non-spec tube problems. To think these would be prevented by including a bias adjustment is something of an insult to you and us. If you put the wrong size tires on your car, do you think changing the pressure will make them right? Please, don’t think this is a blanket indictment of the other guys selling tubes — it isn’t. And their tubes aren’t all bad either. It just doesn’t make sense to pay more of your hard earned cash for tubes that were probably made in the same Russian or Chinese factory and which have the possibility of being outside the performance window we select for your amp. And it pains us to hear the hype and mystique built up around biasing when twenty-five years of evidence affirms our decision to make bias circuits that “never need adjustment”. How much money and trouble that has saved Mesa/Boogie players you couldn’t estimate. Our rigorously tested and hand selected tubes are available at your nearest Mesa/Boogie Pro Center or from us directly. Nobody offers better price, quality or warranty than we do ... so why swerve? Next time we’ll talk about our part in developing the great Sylvania STR 415 type 6L6 and how we’re on the verge of seeing something fairly close reappear on the market. Remember, we still have some of these super rugged mondo-bottles available for older amps — Boogies only please! Until then, Relax, Breathe and Nourish your soul! Cheers! Mesa/Boogie Ltd. Randall Smith Designer and President


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#32 mtreehugger

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Posted 13 February 2015 - 06:21 PM

I guess I will say something since I got called out here...Please keep in mind that what I post on these boards is my opinion based on my own experience. I have been working on and using tube amps for little while and I have my own strong opinons and know what I like and how I like my amps to operate...I have been using Mesa tubes in my DT50 for about 4 years now...same thing in my DT-25....I do use a GTSAGAX7 for my inverter...I have had no issues, my amps have lower noisefloors than they did with the stock tubes and sound fantastic...Same with my SVMK1 and SVMK2...anyhoo...take that with a grain of salt...what works for me, may not work for you...

 

 

 

Thanks for the post!  You know that when I "called <you> out" that I did it in a deferential, admiring way, right?

 

Okay, so this guy and psarkissian are both saying to stick with the original tubes and don't mess with the bias (ceptin ya kaint bias a boogie).  And they're both saying that messing with these things can put your amp on a tech's bench.  But you aren't following that advice.  Care to divulge the bias voltage in your DT50?


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#33 spaceatl

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Posted 13 February 2015 - 07:29 PM

You are most welcome and thank you...I do not mind being called out for what I post here. I will always do my best to try can clarify my opinions as best I can in text. Sometimes it's really difficult to get the context across.

 

I think the Line 6 Service Tech's general advice is extremely sound. Stick to the production design...A user that is really new to tube amps is probably better off sticking to the recommended valves...Odds are they are going to get something close to what RB/Line6 intended and their amp should sound like RB/Line 6 intend the production DT50 to sound.

 

If the specially marked EH valves are traced as tightly as they are indicating, then switching them out and setting the bias to around 35-37 mv with multi-meter should work just great 99% of the time...

 

hmmm, my DT-50....Well, I have only done a few things to my DT-50 thus far...Mounted an NL4 speakon for my cabinets, changed the tubes and changed the speaker. V30s are really a speaker that I love to hate...I think I have 4 of them sitting around. They just are not a good fit for me...I don't like Celestions for my tone...I totally enjoy listening to other players that use them...just not my cup of tea. My first amp was a Mesa SOB loaded with an EV12L....That basically must have imprinted on my DNA and I have always gravitated towards high rated PA type speakers ever since (circa 1982)...

 

I have some prized Madison Minstrels in 212 cabs that I adore and are still in good shape...they work very nicely for extension cabs in combos which what I dig for my rig...however, for the DT50 I went a different route on its internal speaker...I found a new favorite...Jenson Jet Tornado 16 ohm...I tried a bunch of speakers with the DT50 and this speaker is just perfect I think...Not only sounds great...but it weighs 4.5 lbs and does not sound like a neo at all to my ears...There is something really cool about running this amp at 16 ohms that I prefer...

 

...Bias...hmmmm...It has been some years since I checked...I think it was around 497 volts on the plates and I think I ended up at 35mv...Not really any different than what it was...I do plan to do a rear bias adjust and test points mod on this amp on the next tube change...Which is really kinda overdue...But I have gotten some really good life out of these...not mushy yet...


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#34 radatats

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Posted 13 February 2015 - 08:45 PM

Here is the bias info from the old forums...

https://www.myflare....e Bias Tips.pdf


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Quit complaining and DO something or help somebody with their issues...


#35 mtreehugger

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Posted 15 February 2015 - 08:31 AM

You are most welcome and thank you...I do not mind being called out for what I post here. I will always do my best to try can clarify my opinions as best I can in text. Sometimes it's really difficult to get the context across.

 

I think the Line 6 Service Tech's general advice is extremely sound. Stick to the production design...A user that is really new to tube amps is probably better off sticking to the recommended valves...Odds are they are going to get something close to what RB/Line6 intended and their amp should sound like RB/Line 6 intend the production DT50 to sound.

 

If the specially marked EH valves are traced as tightly as they are indicating, then switching them out and setting the bias to around 35-37 mv with multi-meter should work just great 99% of the time...

 

hmmm, my DT-50....Well, I have only done a few things to my DT-50 thus far...Mounted an NL4 speakon for my cabinets, changed the tubes and changed the speaker. V30s are really a speaker that I love to hate...I think I have 4 of them sitting around. They just are not a good fit for me...I don't like Celestions for my tone...I totally enjoy listening to other players that use them...just not my cup of tea. My first amp was a Mesa SOB loaded with an EV12L....That basically must have imprinted on my DNA and I have always gravitated towards high rated PA type speakers ever since (circa 1982)...

 

I have some prized Madison Minstrels in 212 cabs that I adore and are still in good shape...they work very nicely for extension cabs in combos which what I dig for my rig...however, for the DT50 I went a different route on its internal speaker...I found a new favorite...Jenson Jet Tornado 16 ohm...I tried a bunch of speakers with the DT50 and this speaker is just perfect I think...Not only sounds great...but it weighs 4.5 lbs and does not sound like a neo at all to my ears...There is something really cool about running this amp at 16 ohms that I prefer...

 

...Bias...hmmmm...It has been some years since I checked...I think it was around 497 volts on the plates and I think I ended up at 35mv...Not really any different than what it was...I do plan to do a rear bias adjust and test points mod on this amp on the next tube change...Which is really kinda overdue...But I have gotten some really good life out of these...not mushy yet...

 

"I don't like Celestions for my tone...I totally enjoy listening to other players that use them..."

 

I often wonder why what sounds great with other players doesn't work the same for me.  Is it because we expect a certain type or velocity of response based on what we heard earlier, and then when we're actually playing we experience something a bit removed...?  Or am I just a bit eccentric as a player?  Hmmm... more on that later, perhaps in another life.

 

With different speakers one might expect different tubes too.  You're a tweaker, that's for sure!

 

So this mod you speak of, I saw some posting on it in other thread(s).  Once completed, are you simply connecting a voltmeter to the test points?  And then there's the question of why:  Do you test and adjust the bias regularly during the life of the power tubes?

 

THANKS!


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#36 spaceatl

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Posted 15 February 2015 - 05:55 PM

Being able to check the bias without having to pull the chassis out of the box means I will check it more often....That is generally the first 8 or so hours on new tubes as they burn in....things can change a little bit...basically, it more of a convenience mod.

 

The metal chassis mount bias pot is less prone to drift than the typical plastic PCB types...The Weber pots are nice and tight...

 

Basically, tubes can go at any time and I like to be prepared for changing them out without have to take the chassis out...


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#37 talwilkins

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Posted 16 February 2015 - 12:35 AM

Being able to check the bias without having to pull the chassis out of the box means I will check it more often....That is generally the first 8 or so hours on new tubes as they burn in....things can change a little bit...basically, it more of a convenience mod.

 

The metal chassis mount bias pot is less prone to drift than the typical plastic PCB types...The Weber pots are nice and tight...

 

Basically, tubes can go at any time and I like to be prepared for changing them out without have to take the chassis out...

That's interesting. Can you show us exactly how you will do this and what bias pot you will be using? I might consider doing this mod on my DT25


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#38 mtreehugger

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Posted 16 February 2015 - 07:11 AM

Being able to check the bias without having to pull the chassis out of the box means I will check it more often....That is generally the first 8 or so hours on new tubes as they burn in....things can change a little bit...basically, it more of a convenience mod.

 

The metal chassis mount bias pot is less prone to drift than the typical plastic PCB types...The Weber pots are nice and tight...

 

Basically, tubes can go at any time and I like to be prepared for changing them out without have to take the chassis out...

What will you check the bias with--a voltmeter?


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#39 spaceatl

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Posted 16 February 2015 - 10:28 AM

right, just moves the stock test points to the back of the amp...

 

here is a thread I did in the old forum regarding my MK1 mods....I don't think the pics are there...I will see if I can dig those up...The hardest part is desolding the pots...But I guess it's a little easier in the DT50 as there is only 1...but this might translated into two pots as the DT's are a balance type single pot...

 

http://line6.com/sup...w/thread/24828/


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#40 Brazzy

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Posted 16 February 2015 - 11:04 AM

What I did was just go with the AMP Heads Bias probe tester which makes it possible to see what both tubes are doing while your turning the bias pot. It's so easy to take the chassis out of the DT50 Head it's pointless for me to modify it.

 

The most important thing is to put "Line 6 Approved Tubes" in it, IMO. This morning I've been playing with the head on Low Volume Mode to check that it works to my expectations as I've spent 4 hours on the High Volume Mode and am happy with it thus far. So far the LVM is working great and as expected. I've been using my noisey strat going right into the front Low and High inputs. I don't even need a noise gate.I've tried all of my other guitars with the good results too.


Edited by Brazzy, 16 February 2015 - 12:13 PM.

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