[Al Skierkiewicz]

OK,
The old 883 and 884 may output 24 volts but they are not designed for that voltage. The breakdown on the FETs is too low. There are a few minor differences between the two. The 883 needs a transorb attached to the power input, the 884 has an internal one included. There was a production run of "blue" 883 which were the preproduction of the 884. I believe another significant difference is the inclusion of the dead-band in the 884 to quiet the output with noisy joysticks.
Please note that the IFI/VEX site has part numbers for the new 883, 884, and 885 controllers which are available in 24 volt versions and available with either 24 or 12 volt fans.