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In Reply to: Silly bias question posted by Todd A. on December 13, 2003 at 11:32:03:
Not so silly -What you really want to know is the "bias current" thru the tube. As a way of assessing this current you can measure the voltage this current produces across a known resistor.
For example the Dynaco ST70 uses a 15.6 ohm cathode resistor. Since the intended bias current for a pair of output tubes is 100ma, using V=IR, 100ma = 0.1 amps across 15.6 ohms will produce 1.56 volts at the bias measurement jack.
Lastly, some schematics include the measured voltage at the grid as a "bias setting". In the case of the Dynaco ST70 example, this would be a measurement of -32v. This unfortunately varies with individual output tubes.
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Follow Ups
- Re: Silly bias question - Gary Kaufman 12/13/0312:00:51 12/13/03 (1)
- Re: Silly bias question - Todd A. 13:10:24 12/13/03 (0)