DL93 must be replaced by DL94 on previous post

At your risk. It is a typo but the same schematic can be used for all sort of different electron tubes. EL94 is also a possibility as the input transformer can bring the volatge up to the same level (say 4V) as needed by DL type electron tubes. In fact the schematic is very similar to the Pleiades V6 battery powered electron tube low noise mic booster. The only difference is that the power amplifier does not need the high Megohm contact potential compensating resistor from anode to control grid (Pleiades bias) that makes the mic booster amplifier operate at say 4V at the anode only. When the context is electron tubes by contact potential we mean the potential created by the electron cloud boiling electrons that makes it difficult for new electrons to escape cathode (when the anode potential is low). When the anode potential is high there is electric field penetration which reduces the negative potential at grid from the electron cloud. But a power amplifier as opposed to a very low noise pre preamplifier, needs higher powe,r hence the high anode voltage together with negative bias in order to keep the anode current reasonably low in order not to destoy the electron type. (The inventor of what is called here Pleiades bias seems to be the inventor of battery powered electron tube guitar pedals, see older posts). Anyway everything in euroelectron is open source, free to use provided other party rights are not infringed.