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Post subject: Rebiasing necessary?
Posted: Sat Sep 24, 2011 5:35 pm
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Do I have to re-bias the power amp if I am replacing with the same type of tubes that my amp came with?


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Post subject: Re: Rebiasing necessary?
Posted: Sat Sep 24, 2011 7:15 pm
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No tubes are exactly alike regardless of what the manufacturers claim. You should always check the bias and adjust it if necessary.

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Post subject: Re: Rebiasing necessary?
Posted: Sat Sep 24, 2011 7:25 pm
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Hi nyaben,

Depends on the amp, and the type of output tubes, preamp tubes need no adjustment. Some amps have no adjustment, or are Cathode biased and don't need adjustment. If the bias is correct to begin with, and you use the exact same replacements, the bias will likely be the same, no adjustment necessary. Depending on the tubes that you use, getting exact replacements may be hit or miss, so it's always a good idea to check the bias whenever output tubes are changed. With GT tubes, you can get an exact replacement using the number and color code of the existing tubes, guaranteed. Tubes from TheTubeStore, and others, also have a number rating, meaning if you use the same number as the existing tubes, the bias should be very close.

Best practice is to always check the bias with new output tubes to be sure. Hard to know where it is set to begin with unless you actually check it (even new tubes can have problems).

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Post subject: Re: Rebiasing necessary?
Posted: Sun Sep 25, 2011 2:36 am
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Yes


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Post subject: Re: Rebiasing necessary?
Posted: Sun Sep 25, 2011 6:20 am
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Thanks...I have a MIA Blues Deluxe and will probably go with the GTs. I suppose I will try to replace all of them (2 6L6s and the 3 12AX7 tubes). I don't have any idea how to re-bias so I may end up taking it somewhere. Any videos, sites worth looking at for a novice like me? Have also heard it can be a little dangerous to attempt if you're not really sure how to do the re-biasing.

I just read that my amp has no bias adjustment pot. I believe the reissue of this amp does.

Also found the following site but I don't see any mention of whether this is for the original or the re-issue:

http://www.electric-guitar-info.com/tub ... asing.html


Last edited by nyaben on Sun Sep 25, 2011 6:31 am, edited 1 time in total.

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Post subject: Re: Rebiasing necessary?
Posted: Sun Sep 25, 2011 6:31 am
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Blues DeLuxe don't have any user adjustments potentiometre. Better find a good tech to bias your new tubes. Only go to a recommended tech .


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Post subject: Re: Rebiasing necessary?
Posted: Sun Sep 25, 2011 7:16 am
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Yep the bias should be checked. The longevity of the power tubes rely on it. Too cold and you'll get the icepick in the forehead tone but the tubes will last a long time, too hot and you'll get pretty early breakup and shorten the tubes lifespan.

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Post subject: Re: Rebiasing necessary?
Posted: Sun Sep 25, 2011 7:33 am
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nyaben,

That website author doesn't know what the heII he is talking about, maybe he should stick to guitars and forget about amps. The BDlx is NOT Cathode biased, it never has been. And Cathode biased amps DO NOT have a bias adjust pot. Also, he says that the tube manufacturer recommends a certain bias current for their tube, this is also BS because the idle current setting for any output tube depends on the Plate voltage of the amp. You set the bias to a percentage of the tubes Plate wattage rating, typically 50% to 70%, so you must consider the Plate voltage AND tube wattage rating.

The BDRI added an adjustment pot, but it is still what is referred to as a "fixed bias" amp, NOT Cathode biased.

I would delete that link and never visit that site again, it is idiotic nonsense mixed with a little bit of fact. :idea:

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Post subject: Re: Rebiasing necessary?
Posted: Sun Sep 25, 2011 7:51 am
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+1 Shimmilou.

This shows us again that we must be wary of what is written on the web


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Post subject: Re: Rebiasing necessary?
Posted: Sun Sep 25, 2011 7:54 am
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So, I could either buy the GTs, replace the tubes and cross my fingers...or pay a tech check/adjust the bias. I was hoping it wouldn't cost much to do this but it looks like it may cost a little more than I had thought to get it right and I do want it done right of course.

Thanks very much for all of your help.


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Post subject: Re: Rebiasing necessary?
Posted: Sun Sep 25, 2011 8:09 am
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If you have a tube amp is because you want a good tone that only tube have. And for having a good tone ( and not only to save your tubes ) you need the good bias.

One thing is sure ; Soon or later you'll need a good tech for your amp, better to search now than when you'll be in a hurry. And you'll play with the best tone right now.
With a bias check you could have the best tone you never hear before with the same amp. I often see wrong bias on brand new amps.

Ask to your friend or other gigging guitarist if they know sa good tech.


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Post subject: Re: Rebiasing necessary?
Posted: Sun Sep 25, 2011 8:11 am
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nyaben wrote:
So, I could either buy the GTs, replace the tubes and cross my fingers...or pay a tech check/adjust the bias. I was hoping it wouldn't cost much to do this but it looks like it may cost a little more than I had thought to get it right and I do want it done right of course.

Thanks very much for all of your help.


Since you need to go to a tech to have an original Blues Deluxe biased, you might want to pick up something like this and have it installed at the same time.

http://torresengineering.stores.yahoo.n ... sdevn.html

However, don't forget that bias can encompass a range of settings which is why some amps work just fine with tubes that are matched to the amp. You just don't want to go too hot or too cold.

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Post subject: Re: Rebiasing necessary?
Posted: Sun Sep 25, 2011 1:36 pm
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Thanks so much for the great suggestions. I think I'll try to find a reputable tech and that kit looks like it would be well worth the money to have that installed at the same time.


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Post subject: Re: Rebiasing necessary?
Posted: Mon Sep 26, 2011 7:02 am
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No way No how...running to a a tech everytime you replace tubes is fanatical :lol:
Replace with the same spec tubes and you are fine...the tubes come pckged in sets and if they are off a little..no harm done. Bias is more tone taste then the damn amp blowing up :lol: So your natural breakup is a little sooner or even a little later...most of us will never notice the slight difference unless they are WAY off...and that is highly unlikely
8)

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Post subject: Re: Rebiasing necessary?
Posted: Mon Sep 26, 2011 7:30 am
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musicmatty wrote:
...Bias is more tone taste then the damn amp blowing up...


Bias is about the tubes life firstly, and must be set within specs to prevent the tubes from red-plating, which could then cause harm to the amp. Breakup is secondary, the bias still must be within a certain range, and there is room within that range for breakup considerations.

So, yes, if your bias is set too high, the amp can indeed "blow up". Ideally, if the bias is correct to begin with, you can replace the tubes with exact replacements and your bias will be very close. But, as has already been explained before, knowing that the bias is correct requires that it is checked, and depending on the type of tubes that are used, getting an exact replacement might be difficult.

And what kind of tube amp do you have musicmatty?

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