The capacitance of the grid condenser is chosen to be around ten times the grid input capacitance and is typically 100 to 300 picofarads (pF), with the smaller value for screen grid and pentode tubes. The resistance and electrical connection of the grid leak along with the grid current determine the grid bias. For operation of the detector at maximum sensitivity, the bias is placed near the point on the grid current versus grid voltage curve where maximum rectification effect occurs, which is the point of maximum rate of change of slope of the curve. If a dc path is provided from the grid leak to an indirectly heated cathode or to the negative end of a directly heated cathode, negative initial velocity grid bias is produced relative to the cathode determined by the product of the grid leak resistance and the grid current. For certain directly heated cathode tubes, the optimum grid bias is at a positive voltage relative to the negative end of the cathode. For these tubes, a dc path is provided from the grid leak to the positive side of the cathode or the positive side of the "A" battery; providing a positive fixed bias voltage at the grid determined by the dc grid current and the resistance of the grid leak. As the resistance of the grid leak is increased, the grid resistance increases and the audio frequency bandwidth at the grid decreases, for a given grid condenser capacitance. For triode tubes, the dc voltage at the plate is chosen for operation of the tube at the same plate current usually used in amplifier operation and is typically less than 100 volts. For pentode and tetrode tubes, the screen grid voltage is chosen or made adjustable to permit the desired plate current and amplification with the chosen plate load impedance. For grid leak power detection, the time constant of the grid leak and condenser must be shorter than the period of the highest audio frequency to be reproduced. A grid leak of around 250,000 to 500,000 ohms is suitable with a condenser of 100 pF. The grid leak resistance for grid leak power detection can be determined by where is the highest audio frequency to be reproduced and is the grid condenser capacitance. A tube requiring comparatively large grid voltage for plate current cutoff is of advantage (usually a low amplification factor triode). The peak