BeePre 2 voltage problem

[PeterG]

I have completed the wiring on the BeePre 2 preamp except for the selector switch and connections to the RCA inputs.  Running voltage tests, I'm showing 6.36 DCV at both tube sockets, but when I insert the 300B tubes, the filaments light up but after about a minute they both go dark.  Is something in the circuit causing a voltage drop?  Whatever it is, any ideas about how to track it down/fix it?  Thanks.

[Paul Birkeland]

You shouldn't have 6.3V DC at both sockets with the 300B tubes installed.  Can you post some build photos?  Are you 100% sure that the sockets are installed in the correct orientation?