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Biasing a VTL amplifier

Posted by Luke Manley (M) on July 6, 2009 at 12:10:11

In Reply to: RE: 12AU7 Tubes for VTL ST-85, also Bias Drifts? posted by Jim McShane on July 6, 2009 at 08:15:50:

You are correct Jim,

The instructions (including Ohms law and what is being measured) are fairly extensively described on our website at http://www.vtl.com/pages/bias.html - the cathode resistor in that model is 10 ohms.

I believe the OP mentions that the slight fluctuation happens whenever his AC turns on, and this would be consistent with the fact that the voltages in that amp are unregulated, so there will be some degree of drift with changes in AC voltage, tube temperature, etc.

The subbing of the 12AU7 for the 12AT7 is another matter, and is not recommended.

• VTL Bias Instructions   (Open in New Window)

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