I'd put only a minimum of 5 mA and a max of 25 mA based on the LED biasing scheme. I suggest more. Like 24.5 mA( or what ever the diodes and your PS are comfortable with ).
Going above 25 mA is going to make the turn-on conditions a bit more critical with the VR tubes. They can stand nearly 100 mA for a short period. Say, 20 mA for the VR string, and 20 each for the 12B4's and that is 60 mA at start going through the VR tubes. NO PROBLEM!
I am running 21-22 mA with the current 12B4 linestage and didn't see improvement above 25 when I tried it.. regards, Douglas
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