Question

The figure shows two identical triode tubes connected in parallel. The anodes are connected together and the cathodes are connected together. Show that the equivalent plate resistance is half the individual plate resistance, the equivalent mutual conductance is double the individual mutual conductance and the equivalent amplification factor is the same as the individual amplification factor.
Figure

Answer 1

The equivalent plate resistance is half the individual plate resistance, the equivalent mutual conductance is double the individual mutual conductance and the equivalent amplification factor is the same as the individual amplification factor

• Both the triodes from the circuit have the cathodes that are linked to a common point.
• They have anodes that are linked together. So, two triodes linked in parallel.
• The plate resistance is attained from noticing the plate voltage’s variation when there is constant grid voltage. So, the plate has equivalent resistance,  

• Rp = rP1 × rP2 + rP2rP1
• When equal plate resistance is found in the triodes, that is, rP1 = rPRP = rP2 = rP2
• For finding the equivalent transconductance
• We should observe the current’s variation with regard to grid voltage when the plate voltage is constant.
• With reference to the grid voltage, now two triodes are in series.
• So, there will be equal transconductance.
• Gm = 2gm
• When there is equal transconductance in two triodes, that is, gm2 = gm = gm1.
• Now the factor of equivalent amplification is,
• μequivalent = RPμequivalent x Gm  
• = 2gm × rP2μequivalent = μ