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Post subject: Custom Vibrolux Biasing question
Posted: Tue Jul 17, 2012 1:25 am
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Today while putting one of the 6L6's back in my CVR,I damaged one of the valves.
I had a set of matched Groove tube 6L6's and slotted them in to replace the original set.
The amp came fitted with Groove tubes rated white 5 and my replacement set is rated white 4 (or the other way around...I can't recall which).
I put them in,fired up the amp and it sounds fine.
With the valves being that closely rated,will I need to have the amp rebiased?


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Post subject: Re: Custom Vibrolux Biasing question
Posted: Tue Jul 17, 2012 5:56 am
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Yes always check bias with new valves , production of valves is not always standard.


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Post subject: Re: Custom Vibrolux Biasing question
Posted: Tue Jul 17, 2012 2:57 pm
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To be safe I will order valves of the same value from my Fender guy...there will get me through the weekend as the amp is fixed bias


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Post subject: Re: Custom Vibrolux Biasing question
Posted: Tue Jul 17, 2012 6:11 pm
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boofhead61 wrote:
To be safe I will order valves of the same value from my Fender guy...there will get me through the weekend as the amp is fixed bias


Yes, the amp is fixed bias, but there is no bias adjustment pot. You can check the bias, but actually changing the bias would require changing parts in the bias circuit. Ontop of that, the vibrato works using bias modulation of the power tubes. Your best bet is to continue to use the same value tubes that came in it originally. You should be safe given the design of the amp.

http://support.fender.com/schematics/gu ... ematic.pdf

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Post subject: Re: Custom Vibrolux Biasing question
Posted: Tue Jul 17, 2012 8:36 pm
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Thanks guys...I spoke to the tech at Fender Australia today and he told me that the White Groove Tubes rated 4 and 5 are very close to the point where it will be fine.
I have ordered the 4's in any case.
The pair I put in a re also a matched pair from the same pack of two.


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Post subject: Re: Custom Vibrolux Biasing question
Posted: Tue Jul 17, 2012 9:05 pm
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boofhead61 wrote:
Thanks guys...I spoke to the tech at Fender Australia today and he told me that the White Groove Tubes rated 4 and 5 are very close to the point where it will be fine.
I have ordered the 4's in any case.
The pair I put in a re also a matched pair from the same pack of two.


A summary of the GT rating system is right here on their home page:

http://www.groovetubes.com/

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Post subject: Re: Custom Vibrolux Biasing question
Posted: Wed Jul 18, 2012 4:31 pm
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Thanks for helping everyone...I really appreciate it...cheers


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