Here's a recent video series I made while restoring one. Emerson 571 restorations:
https://www.youtube.com/playlist?lis...GgvlCTnETIpOJK
6.3 volts RMS or 6.3 volts DC. It's not critical. +/- 10% is fine. Don't expect your Sencore analog meter to be perfect unless you've recently calibrated it