[Amps] 3-1000Z - Filament Voltage

[rob]

Greetings,

I have a Harris RF-104 with a 3-1000Z tube.  I have several questions regarding the filament voltage.  

The Eimac spec. sheet that I have lists the filament voltage as a nominal value of 7.5 volts with no min or max values 
shown (unlike the 3-500Z spec. sheet which has min/max values).  The Harris RF-104 that houses and powers the 
tube has a spec. of 7.8 volts.  As I've had to adjust the filament transformer taps to achieve 7.8 volts (due to different 
line voltage here), I was wondering if:

1.  There a preferred voltage to run the filament at?

2.  There a loss of tube life running the filament voltage too low or high?

3.   There a practical tolerance for the filament voltage?

Any information would be appreciated.

... 73 

Rob Brennen VE6TR