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> Pre Amp Tubes, need to know
skulptor
post Jan 7 2008, 08:43 AM
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If I want to experiment with different preamp tubes do I still need to rebias the amp or is that only for power tubes?

and can I swap say a ecc83 for a 12ax7, is there any difference?

Does anyone have their own tube prefernces?
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Skewlbuzz
post Jan 7 2008, 09:21 AM
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According to this article http://en.wikipedia.org/wiki/12AX7 the ECC83 and 12AX7 are one and the same. ECC83 is made in Europe and the 12AX7 in the states or something.. This is as much as I can help, dunno much about amps or tubes, so can't tell if they would sound different :s


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USAMAN
post Jan 7 2008, 12:14 PM
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Preamp tube replacement does not require rebias...swap away.

This post has been edited by USAMAN: Jan 7 2008, 12:14 PM


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Ivan Milenkovic
post Jan 7 2008, 12:18 PM
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I don't think you have to rebias the amp if you change one tube in the preamp. Try to google around to see what character other preamp tube models have.


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KloCkWorXx
post Jan 7 2008, 12:42 PM
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QUOTE (skulptor @ Jan 7 2008, 02:43 AM) *
If I want to experiment with different preamp tubes do I still need to rebias the amp or is that only for power tubes?

and can I swap say a ecc83 for a 12ax7, is there any difference?

Does anyone have their own tube prefernces?


u dont need to re bais your pre amp tubes, and if your amp has a fixed bias u dont need to bias it w/ power tubes just get a matched quad... i have a 5150 with JJ power tubes and tung sol 12ax7 n sound really good, im going for the ruby 6l6gc next cause they are only usd $50 for a matched quad compared to 120 for the JJs.. a good website to get tubes is (thetubestore.com) and groove tubes are just relabeled tubes waste of money..


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Andrew Cockburn
post Jan 7 2008, 01:52 PM
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But you have to be careful just dropping in different preamp tubes ...

Some are interchangeable, for instance a 12AU7 is a lower gain version of a 12AX7, but you have to make sure that the voltages are within range for the new tubes etc, which takes some knowledge of the circuits and tube specs.

Most preamp tubes are self biased, which means they are preset by a resistor value built into the board, so rebiasing would require you to unsolder and resolder a different resistor in any case.

However, in general correct biasing is much more important for power tubes.

And another great tube store is tubedepot.com


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Joe Kataldo
post Jan 7 2008, 05:14 PM
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QUOTE (skulptor @ Jan 7 2008, 08:43 AM) *
If I want to experiment with different preamp tubes do I still need to rebias the amp or is that only for power tubes?

and can I swap say a ecc83 for a 12ax7, is there any difference?

Does anyone have their own tube prefernces?


What amp do you have? If is something I've tried I may suggest shortcut to great tone

This post has been edited by Joe Kataldo: Jan 7 2008, 05:16 PM


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Muris Varajic
post Jan 7 2008, 05:27 PM
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Rebias is usually needed for power tubes but NOT always,
as Andrew said,some preamp tubes use different voltage,
it's not huge difference in voltage tho but still enough to make small issues.
I'm I correct here Andrew?Tony?


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ace_frehely
post Jan 7 2008, 05:31 PM
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You dont need it. smile.gif


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Andrew Cockburn
post Jan 7 2008, 06:20 PM
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QUOTE (Muris @ Jan 7 2008, 11:27 AM) *
Rebias is usually needed for power tubes but NOT always,
as Andrew said,some preamp tubes use different voltage,
it's not huge difference in voltage tho but still enough to make small issues.
I'm I correct here Andrew?Tony?


Exactly! Its usually close enough that you will get away with it for preamp tubes, but it isn't 100% certain smile.gif

You need to be more careful with power tubes as they handle some serious power and voltage and things can go wrong quickly if you run them out of spec.


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Saoirse O'Shea
post Jan 7 2008, 06:59 PM
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Spot on as far as I know Muris smile.gif .


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Muris Varajic
post Jan 7 2008, 07:57 PM
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QUOTE (Andrew Cockburn @ Jan 7 2008, 06:20 PM) *
Exactly! Its usually close enough that you will get away with it for preamp tubes, but it isn't 100% certain smile.gif


So what damage can we expect if there's some larger voltage difference?

Every preamp I've had so far is filled with 12ax7 so I'm not of great experience here...

This post has been edited by Muris: Jan 7 2008, 07:59 PM


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Sabbz
post Jan 7 2008, 08:33 PM
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As everyone's said, you don't need to adjust the bias when switching out preamp tubes, just make sure they're the right voltage and whatnot. Go to www.eurotubes.com and send Bob an email with ANY tube/amp questions you may have. He'll answer them within 24 hours and if you need more help, he'll actually walk you through the process.


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Joe Kataldo
post Jan 7 2008, 09:32 PM
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www.eurotubes.com is a really good source for tubes and help


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skulptor
post Jan 7 2008, 09:57 PM
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QUOTE (Joe Kataldo @ Jan 7 2008, 08:14 AM) *
What amp do you have? If is something I've tried I may suggest shortcut to great tone



the amp im referring to here is a Marshall AVT150. I also have a Crate Palomino v16 tube amp, a v8, and an Ampeg vintage club 5212 is all I have for Tube amps. The marshall is just a hybrid though, it has 1 preamp 12ax7 and solid state output and it now has a GrooveTube 12ax7r (2 hardness)
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Andrew Cockburn
post Jan 7 2008, 10:17 PM
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Worst case you will overheat and destroy the tube, that should be the only damage. You will notice the whole top plate glow red, then there will be no more sound smile.gif


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skulptor
post Jan 7 2008, 11:28 PM
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QUOTE (Andrew Cockburn @ Jan 7 2008, 01:17 PM) *
Worst case you will overheat and destroy the tube, that should be the only damage. You will notice the whole top plate glow red, then there will be no more sound smile.gif


How do you like the epi amp? I have been eyeing that one from musians Frnd magazine but havnt been able to find one to play on. I have really been attracted to low watt tube amps lately.
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Andrew Cockburn
post Jan 8 2008, 12:00 AM
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QUOTE (skulptor @ Jan 7 2008, 05:28 PM) *
How do you like the epi amp? I have been eyeing that one from musians Frnd magazine but havnt been able to find one to play on. I have really been attracted to low watt tube amps lately.


Its great for the money - tonewise you don't get a super amount of distortion, but it is good for a clean bluesy kind of sound.


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Muris Varajic
post Jan 8 2008, 01:53 AM
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QUOTE (Andrew Cockburn @ Jan 8 2008, 12:00 AM) *
Its great for the money - tonewise you don't get a super amount of distortion, but it is good for a clean bluesy kind of sound.


Then add some dist pedal and ROCK the house biggrin.gif

Did I say I don't have any combo amp atm???
Must get some,soon dry.gif


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Andrew Cockburn
post Jan 8 2008, 02:02 AM
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QUOTE (Muris @ Jan 7 2008, 07:53 PM) *
Then add some dist pedal and ROCK the house biggrin.gif

Did I say I don't have any combo amp atm???
Must get some,soon dry.gif


I've got one - a Cockburn A.C.1 smile.gif

Did I mention that last night I tried to record Bb Beginner with it ? Didn't quite get a sound I liked yet, it was still too clean, but starting to sound cool smile.gif Think I'll try and add a distortion pedal short term, and redesign the preamp a little longer term.


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