Here's the National Video datasheet for the 10ADP4
https://frank.pocnet.net/sheets/201/1/10ADP4.pdf
They claim "The low filament current reduces the amount of heat produced and lends itself to a compact TV design."
Umm
Filament = 8.4 VAC @ 0.45A = 3.78W
compare that to the standard
6.3 VAC @ 0.6A = 3.78W
Yes, big savings
