Minimum filament/heater voltage for Valve/Tube amplifiers
The RCA receiving tube manual RC-23 is quite vague about the amount of permissible variations, however it does warn that insufficient filament voltage can lead to degraded performance and reduced tube life. Of course excessive filament voltage can also shorten tube life. 

Since tubes were normally operated from unregulated mains transformers, I would think your -11% would be acceptable, but perhaps not if that nominal voltage also has a large tolerance and/or you're working the tube close to the maximum ratings.