Hey-Hey!!!,
I think that GK71 is closest to the 813. not that I have used either yet. I am leaning towards lower voltage filaments. the ratio of filament AC over DC g1 bias looks like an important one to make small...The 813 is a DH valve with a 10V/5A filament. The Russians did seem to go for 20V filaments for some reason. The 4E27 I am experimenting with is a 5V/7A filament. I think it's a worthwhile valve to play with. I did not turn up any detailed info on the GU13
and now for the SE thing....I have not yet built a SE power stage. No plans to do SE either.
regards,
Douglas