After the introduction of the 845 amplifiers with an indirectly heated driver, here is Thomas Mayer’s new top of the line single ended 845 mono amps with a directly heated driver. The Elrog ER887 is a completely new tube type especially developed for these amps by Deutsche Elektronenröhren Manfaktur GmbH.
As 845 requires a large voltage swing at its grid an amplifier with all directly heated tubes would normally require minimum stages due to the low amplification factor of directly heated triodes.
The all-new ER887 is a big directly heated triode with thoriated tungsten filaments. No similar tube type was ever made so far. It shares the identical glass bottle/Jumbo 4 pin base as the 845 and operates at similar plate voltages.
You can see in the photo, that power supply uses a hybrid bridge with two ELROG ER274A and two 6AU4 TV dampers for the rectification of the plate voltage. The complete set of four chassis takes a whole square meter of floor space.
Link: here.