The ECC40 is a tube
with characteristics between the ECC82 and the ECC83. It has a Rimlock socket.
The genuine ECC40 tubes have
silver plated connectors (which usually look a little bit dirty).
The ECC40 can be found
in several Siemens power amps and preamps. In the later tube amps the ECC40
tubes were changed for ECC82s or ECC83s.
All ECC40s shown
were made by the Philips company.