Hi Patrick,
But no manufacturer who made large numbers of amps ever put a pentode CCS in any
home audio gear because it was never ever thought to improve the
sound or
lessen the overall THD measurements of the amp.
Just for your records,
Cary mades a such differential power amp with tube CCS & without zero NFB:
http://www.caryaudio.com/products/classic/CAD211FE.html
Hp