In the quest of refining the 6C4C push-pull design I started not long ago, it was suggested by 45 to try a different driver. The famous E180F russian equivalent with gold grid: 6J9P-E. So I went back at my design and replaced the 4P1L driver with the 6J9P-E. Instead of filament bias, the bias was provided by a pair of red LEDs. The low dynamic impedance of these avoid the use of a bypass capacitor. Setting the operating point with the existing supply is a bit tricky but I found that Va=210V / Ia=14mA provides good swing and minimum distortion. Biasing the valve at around -3.7V keeps the valve away from grid current which will increase the distortion unnecessarily. So here is the circuit: