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This data sheet applies for the 5Z3-Mesh and 5U4G-Mesh, which are electrically identical, apart from the sockets. 5U4G-Mesh uses as Octal Socket socket, of which only five pins are used (and one of those is electrically not connected). 5Z3-Mesh uses a four Pin UX4 socket.
These are direct replacements for the historical 5U4G or 5Z3. They can not replace 5U4GA or 5U4GB which are different tubes. See Note 4
Note that the Emission Labs® tube is somewhat larger size than the historical tubes. Check below at mechanical data, for details. Like most NOS rectifiers, also the EML rectifiers are Slow-Start tubes, protecting the power supply and the whole amplifier to some degree. The delay time for first function is 2 seconds, and the delay for full current is 7 seconds.
Read More Here: http://www.emissionlabs.com/datasheets/EML5U4G.htm