Single Ended Stereo Preamp - Shared power supply

[Cqwet Dbdfte]

For a tube preamp, the channels need a much better decoupling each from the other. Do it with two chokes combined with electrolytic caps for each channel. Do not parallel caps without separation with a resistor or choke

Chokes are OK for low voltage loss, not needed for pre amps drawing a few mA. Resistors are better, smaller, cheaper, flatter freq response.
Cathode followers challenges the power supply's internal resistance, using this as its "plate load".
Some use the same resistor values for driving stage of cathode follower/buffer to keep load current near constant. Not always possible.
An active regulated power supply will have the lowest output impedance and have the lowest load induced voltage changes, even with a couple of different channels connected.
80 - 100 years ago this was not in the cards.