For example if a 2 volt heater Nuvistor electron tube is used, eg 2DV4, 2DS4, 2CW4:
It can be powered by an AA 1.2V with the additional benefit of underheating for better noise figure.
If 2 Bulgin AA battery holders as used then:
One can power the heater.
The 2 in series can power the anode to a healthy 2.6V. A Pleiades bias resitor can be found for optimum noise performance.
In case the heater battery is nearly discharged, the batteries can be swapped giving a doubling of operating time in case of emergency. The discharged battery will have no issue in supplying the tiny anode current. And the fresh battery will supply heater current.
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