I'm using it in my SE300b amp. Before I had 6sn7 in a "classic" arrangement with 2 capacitor coupled common cathode stages and it was already very good. Then I tried Thorsten-suggested pentode single stage drive, but didn't like it at all - it sounded agressive although it had better THD specs. Finally, last year, a friend gave me 2 ecc99's to try. I made 2 DC coupled common cathode stages and it really was singing! Great sound and excellent specs. I'm listening to it ever since. 
hi konstantin,
I can't give the exact schematic (couldn't find it anymore) but as I remember -
first triode has 22k anode resistor, 180R cathode resistor, 100k input resistor and 330R gridstopper.
Grid of the second triode is via 330R gridstopper resistor connected to the anode of the first triode and that triode has 6k8 resistors on anode and cathode. 6k8 cathode resistor is bypassed with 10uF capacitor. Second triode's anode is via 0.22uF cap and 820R gridstopper connected to 300B's grid and there is 180k input resistor connected between cap/gridstopper junction and ground. 300B's cathode resistor is 1k and is bypassed with 100uF.
B+ is 450V for 300B and ca. 350V for ECC99. Both tubes are DC heated.
I can't give the exact schematic (couldn't find it anymore) but as I remember -
first triode has 22k anode resistor, 180R cathode resistor, 100k input resistor and 330R gridstopper.
Grid of the second triode is via 330R gridstopper resistor connected to the anode of the first triode and that triode has 6k8 resistors on anode and cathode. 6k8 cathode resistor is bypassed with 10uF capacitor. Second triode's anode is via 0.22uF cap and 820R gridstopper connected to 300B's grid and there is 180k input resistor connected between cap/gridstopper junction and ground. 300B's cathode resistor is 1k and is bypassed with 100uF.
B+ is 450V for 300B and ca. 350V for ECC99. Both tubes are DC heated.
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