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Post subject: Fender Blues Deluxe Reissue Rebias
Posted: Sat May 13, 2017 4:53 pm
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Yesterday I rebias my Blues Deluxe Reissue from 59mv factory settings to 68mv in order to have hotter sound. The problem is that after rebiasing the amp, now I have a white noise to the amp even when the guitar is not connected to the amp. Is that logical?


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Post subject: Re: Fender Blues Deluxe Reissue Rebias
Posted: Sat May 13, 2017 5:58 pm
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Perfectly logical. Tubes are designed to perform properly within a given range of parameters -- plate voltage, screen voltage, cathode current, idle bias, etc. Where these various values intersect is generally a tube's optimum environment, also known as the "envelope". It has a floor and a ceiling and if either is exceeded then problems often occur -- sterile amp tone, tubes red-plating, crappy S/N ratio (ie: the white noise you've described). If you want a hotter sound, try an outboard device such as a OD pedal. Abusing your tubes is not the best way to achieve it.

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Post subject: Re: Fender Blues Deluxe Reissue Rebias
Posted: Sat May 13, 2017 6:19 pm
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My new bias is on 68mv which is according to fender and the GT tube manufacturer in the safe side. GT gives up to 70mv. Should I return the bias to 60mv?


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Post subject: Re: Fender Blues Deluxe Reissue Rebias
Posted: Sat May 13, 2017 7:13 pm
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I believe you'll be fine at 68 mv.


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Post subject: Re: Fender Blues Deluxe Reissue Rebias
Posted: Sun May 14, 2017 2:17 am
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Schematic show 485 volts on 6L6GC plates
At 70% plate dissipation you can go to 86 mv / ma bias . 43 mv per tube. Did each tube drop 43mv ? You can't read it.

Other 6L6 need less than 86 mv
Your tubes are not 6L6GC or they are unbalanced, one is weak or one have small short ?


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Post subject: Re: Fender Blues Deluxe Reissue Rebias
Posted: Sun May 14, 2017 2:21 am
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Blue Notes wrote:
I believe you'll be fine at 68 mv.


Rodidie, I am at 68 mv now and I have white noise. This is my issue.


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Post subject: Re: Fender Blues Deluxe Reissue Rebias
Posted: Sun May 14, 2017 2:34 am
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Spy wrote:
Blue Notes wrote:
I believe you'll be fine at 68 mv.


Rodidie, I am at 68 mv now and I have white noise. This is my issue.


Go to 60 and report, nothing plug to amp when you do bias, vol to 0
And read my first answer


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Post subject: Re: Fender Blues Deluxe Reissue Rebias
Posted: Sun May 14, 2017 6:42 pm
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White noise is generated when electrons bounce off the plate instead of being absorbed by the carbon coatings. They hit, then leave with a pop
So turning up the bias will inevitably raise the white noise, relative to plate current..
Raising bias also increases the gain of the main stage. This amplifies the noise generated by the preamp stages more. So quiet tubes in the preamp is important.
White noise is only generated by tubes. The coatings on the plate are critical for quiet tube performance. If the GTs are only quiet up to 60, that's their personal limit of good sound. Other tubes can perform better. I use JJ power tubes.


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