2.4ghz electronics is 3.3 or 5v. the radios have regulators in them to step down the 12v of the batteries to the voltage the transmitter part runs on
this mod for the DX6 (8xAA) shows it
http://www.dimensionengineering.com/...ektrum_mod.htm
so yes, they're designed to run on 12v but little cheap linear voltage regulators get really hot dissipating that much voltage (8.7v). They also waste a tremendous amount of power as heat - which means you get less runtime - and this is for a spektrum radio never mind a cheapie. these radios have closed cases and no heatsinks on the regulators which is a recipe for burned silicon.
What this means is you will be ok running the radio (this applies to all 8xAA radios not just the GT3B) as long as you dont run it for hours on end, you'll be giving the regulator cool down time before it gets into thermal runaway.. but i keep seeing threads "i left my radio on accidentally and now even with new batteries i have no range"
the reason they get no range is their regulator has partially burned out and no longer supplies the correct votage to the transmit part of the circuitry.
it's possible being a high end radio that the futaba 2pl has proper regulation. More likely you don't run it for hours and hours.
It's also very likely I am falling into the engineer's failing of overengineering everything. I have a habit of doing that. Thought it would be useful info for the folks here, especially those who (like me) do not like LiPo tech, or for one reason or another don't run it.. my electric cars run LiFe or NiMH batteries, i have Li-Ions in my nitro, soon to be upgraded when i can figure out where to fit them, to LiFe... i'm torn between using 3s LiFe or 9s NiMH (eneloop) for my GT3B.. will need the power saving of a proper regulator if i run LiFe as the cells that fit are only 1100mah and i do run for hours on end.. often running my electrics till all my packs are flat, then getting the nitro started
