[Mondial]

You really do want to replace the 6L6 with the correct 6F6

At -14 V grid bias, the 6L6 will draw 72 mA from the power supply while the 6F6 at the same grid bias only draws 45 mA, so the 6L6 puts an additional load of 20 to 30 mA on the supply and power transformer. Not good for long term reliability and the extra current through the bias resistor will also throw off the other bias voltages.