About 10 years ago I used this tetrode driver which I loved. The 24a. It has hungry filaments, albeit a lovely sound. I probably lost a few readers by now, but don’t care. The 24a into the 45 Single ended, was a great choice, no wonder why Torsten praised this valve.
I settled with the following driver which worked well for me. The 24a is carefully operated at 8mA and 80V on the screen to minimise distortion. This way you can get about 35.5dB (x60) gain stage with about 160Vpp output at 0.5% THD. Yes, more H3 component than a triode, but sounds really nice:
Simple and effective gain stage for a 2-stage amplifier. The output valve could be anything of your choice: 2A3, 45 or even 300B.
The hybrid mu-follower use R1 to set the gain of the tetrode stage (I covered this before many times) and the stable mu-output also feed the screen regulator (Reg 1). I made also a PCB for this regulator, so the driver footprint is very small.