Presented are two new equations for three-halves-power law vacuum tube models fitted to actual devices. First, an equation involving the vacuum tube’s electrode voltages used as the variable of a polynomial that is fitted to tube amplification factor characteristics is presented. Second, a current division equation that combines grid current calculation of existing empirical formulae and caters for screen grid current at low plate voltages, a situation not handled by these, is presented. Included is an exponential function to smooth the discontinuity in plate current due to the model’s conditional treatment of grid current when tube operation moves between negative and positive control grid regions, to aid computation of derivative based tube properties such as transconductance.
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