[Milsurplus] GRC-9 question

[Hue Miller]

Say, a question on GRC-9 schematic.The pilot lamp circuit - why does it switch out 1/2 the 3V4 heaterwhen the pilot lamp is engaged? Only reason i can think of, is you're olusing a well-used receiver battery, and the voltage might go down( change ) when otherwise you push the lamp button - and the filament voltage of the whole receiver drops, and the frequencyof the weak CW signal you're searching for changes.....???What say?tnxHue Miller