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| previous: M Cook I've been wrestling with this for t... -- 8/3/2000 4:54 PM |  |
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Re: cathode caps and resistors
 8/3/2000 6:30 PM |
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Reverb | Re: cathode caps and resistors Greetings, In your message you used the correct formula, but your reasoning was not straight. As always, V = I x R You say you have 2.5V (call this Vold) measured across 820 ohms (call this Rold), which does give you 3mA (call this Iold) according to V = I x R. Now, you want to split the current evenly between two separated triode stages. This means you want 1.5mA per stage (call this Inew), with the voltage to remain at 2.5V bias level per stage (same Vold as before). Now take a look at the equations: V = Inew x Rnew = Iold x Rold Inew = 1/2Iold, so: V = 1/2Iold x Rnew Rearranging, you get: Rnew = V/(1/2Iold) = 2 x V/Iold Substitute in know values: Rnew = 2 x (2.5V/3mA) = 1.66k (double 820) As you know, 1.5k is used since it is a standard value and gets you close enough. Hope this helps and doesn't confuse, Reverb |
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| M Cook Thanks Reverb! :) |