Uses German Steel 10-pin (Y10A / Stahl 10 / G10A) base, which is not a standard octal, noval, or magnoval socket. Requires a dedicated Y10 socket.
A Magnoval-based variant also exists (EL156 Magnoval) but is not pin-compatible with the original Y10A version.
Max anode dissipation differs by bias type: 50W with cathode (auto) bias, 40W with fixed bias.
Screen grid dissipation limit depends on drive level: 8W at Ug1eff=0, but 12W permissible with speech and music signals.
In triode connection, max combined screen voltage is 500V (vs 450V in pentode mode). Telefunken recommends keeping combined anode+screen dissipation below 35W in triode mode.
A 100 Ohm screen stopper resistor is required before the screen grid in push-pull AB operation.
Pins 3 and 4 are internal connections (beam plates) and must not be connected externally.