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K&K Audio / Lundahl Transformers Welcome! Need support, you got it. Or share youe ideas and experiences. |
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K&K Audio / Lundahl Transformers Welcome! Need support, you got it. Or share youe ideas and experiences. |
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In Reply to: Re: Grid resistors would ruin the source impedance? (nt) posted by Tre' on September 1, 2003 at 10:03:27:
Tre,The source impedance "seen" by the grid of the output tube is essentially that of the driver tube plate impedance reflected through the transformer ratio. The grid leak resistance has nothing to do with this. If the driving tube has a plate impedance of 10K and the transformer ratio is 1:1, then the grid "sees" a source impedance of 10K. If the transformer ratio were 1:2, then the source impedance is 40K (the impedance ratio is the square of the voltage (turns) ratio.
However, you are right about the grid leak resistance being the load for the driver stage (at frequencies below which the Miller effect is significant). One of the good things about coupling driver to output with a transformer is that the output grid sees a very low DC resistance (good for tube runaway prevention), but the driver doesn't have to drive that nasty grid leak resistor, because there isn't one! With cathode biasing, the other end of the IT secondary goes to ground and with "fixed" bias it goes to the negative bias supply; no resistors are necessary.
Hope that this helped.
Kevin Carter
K&K Audio
www.kandkaudio.com
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Follow Ups
- Re: Grid resistors would ruin the source impedance? - KevinC 12:38:29 09/01/03 (0)
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