WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
also, not sure if this helps or which 5687 you're using but .. from hearsay,.. I believe the philips 5687 are bright and worse tubes than the GE versions