matter where you go....... there you are" Buckaroo Bonsai
No matter which switch is thrown first... the filaments will come on FIRST ! Subsequently, when the second switch is thrown...
the B+ will come up.
When all is powered up.... the next switch (either) to be thrown will turn off the B+ before the filaments are turned off with the last switch operation.
source: 1941 "The Radio Handbook" 8th edition.