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Old 12th January 2013, 06:39 PM   #1
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Default Bias mods

Hi,
I will build soon my vavle preamp. Before begining my construct i would like to add an adjustable bias. Indeed, in order to change voltage i have to change two resistors : one of 660R/20W(It's expensive) and one of 4K7/11w... the process is not very convenient...
I try to discover how i can add 2 pots bias instead of the two resistors ?


Thank you in advance for your help.

ps: i have found this schematic on the web, do you think it is possible to adapt it to resolve my problem ?
http://home.comcast.net/~jbjdav26/in...ual%20bias.jpg
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Old 12th January 2013, 08:42 PM   #2
DF96 is offline DF96  England
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Why do you want to adjust the bias on your preamp? Do you mean the DC power supply voltage B+/HT?

What problem are you trying to solve?
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Old 12th January 2013, 09:10 PM   #3
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Looks to me that the power supply you posted is intended for a power amplifier, rather than a preamp.
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Old 13th January 2013, 02:03 AM   #4
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A pre amp will not need 20W resistors.

Bias is not done at the power supply, it's typically done at the cathodes.
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