DH filament side matters?

[Seavan]

This is the first time I test directly heated tube, so probably a stupid question. I just tested 6C4C, a Russian analog of 6B4G. The plate current was changing from 37mA to 70mA depending on the filament side (contact 2 or 7) I used as a cathode. Does it make any sense?

http://www.goldenmiddle.com/files/6S4S.pdf

 

[Seavan]

I figured it out. I used DC for filament supply.

 

[euro21]

The plate current was changing from 37mA to 70mA depending on the filament side (contact 2 or 7) I used as a cathode.

Connect 100R to both pin (2 and 7) and connect other sides together. This will be the "centered cathode".