• 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.

Universal tube preamp PCB, ECC99/6N6P/ECC88/ECC85/6922/6DJ8 etc. MU follower or SRPP

If there is no hum. The powersupply is good enough.

You must look at the grounding between source and preamp or preamp and housing. Better is no connection between input plug and chassis and/or connection between preamp ground and housing.

How looks the source/volumecontrol you use?
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