Bootstrap ohmic wattmeter

The multiplier of this wattmeter employs a vacuum triode as a linear conductance which, by Ohm´s law, generates a signal proportional to the product of two input voltages. The conductance offered by a triode to an incremental voltage at the anode over a direct voltage varies linear]y with the grid voltage; therefore, the incremental current through it is proportional to the product of its anode and grid voltages. Bootstrap circuits are used to maintain the direct voltage at the anode. It is a true multiplier and maintains its accuracy even for complex waveforms. The instrument developed has 10 power ranges ranging from 10 mW to 300 W and is suitable over the complete audio-frequency range. Its overall accuracy is better than ±7.5% and for current signals greater than a quarter of the range, it is better than ±5.0%.