08-20-2013, 11:27 PM
Scott, I am not sure where you are getting your tube data, but you need the characteristics under class A conditions, which is how the 45's operate in your radio. Average plate current only increases when in AB mode where the grids are actually driven positive.
In true class A, the average plate current remains constant, the instantaneous current of each tube varying from zero to twice the average value when driven to full output. So in your case, each tube draws an average of 30 mA, or 60 mA total for two tubes.
If Philco specifies a load resistance of 6700 ohms, then this is the value I would use as it is the one found to be optimum under the actual operating conditions of the tubes.
In true class A, the average plate current remains constant, the instantaneous current of each tube varying from zero to twice the average value when driven to full output. So in your case, each tube draws an average of 30 mA, or 60 mA total for two tubes.
If Philco specifies a load resistance of 6700 ohms, then this is the value I would use as it is the one found to be optimum under the actual operating conditions of the tubes.
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