Why High Plate Voltage in 2A3 AMP?

Thank you, Ed and Herman.
Having graduated from building a couple of kits. I feel that I am ready to build one from scratch. Researching schematics, gathering parts, etc. Hence the question. It will be a while for me to understand your insight completely, however from this thread I have learned several useful things.

Another way to do bias is with batteries (e.g. rechargable lead-acid usually). The positive side goes to the filament/cathode, neg to ground, and the current passing through it to ground keeps the batteries recharged. Sometimes people throw an LED in there too to adjust current draw.

Scratch-building is the way to go, btw. ;-) Stop over to TubeDIY on AA sometime for some real fun discussion on that.

-Ed

The reason you see 300B preamps and not 2A3 preamps, is that low voltage gain is considered optimum for a good preamp...?