• 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.

Valve Pre Amp & Class D Power Amp

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Probably there is some dc leakage at the output of your tube pre that your tripath amplifier is not happy about. Try waiting a few minutes after you turn on the pre-amplifier before turning on the tripath, this is assuming that the output caps in your tube pre are ok.
 
Hmmmm. Sound peculiar, alright. You could post this to the ClassD forum, if you haven't already. DC on your valve preamp outputs is a possiblility, but I think that the T-amp should be immune to this, as it is AC coupled on the input. My best guess is that the T-amp is somehow sensitive to the grounding (earthing) arrangement. On my T-amps I make sure to isolate the RCA inputs from the chassis, as well as B-.

Try lifting the ground on your pre temporarily and see if that helps. If you have a multimeter, check for DC on the preamp outs. Maybe your preamp has some issues if that is the case.
 
My GG has DC at output when switch on (6th second) and then die down to normal afterward. My UcD has protection at the input. It cut the amp off when overloaded. However, I still force myself to observe the rule of power on sequence and delay. I am building a time delay in the GG output to cover the rare case of main power recovery after failure.
 
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