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Can I use a class D amplifier with a Tube pre-amplifier?
Fundamentally there is no problem of course. However, most tube preamplifiers are designed alongside tube power amplifiers which are always AC coupled. As a result, many tube preamplifiers lack precautions against turn-on/turnoff transients. Some are liable to produce the full anode voltage at their outputs during turn-on and turn-off. We find that a large proportion of repairs are due to tube preamplifiers discharging their output caps into the UcD™ input circuit. Note that most solid-state amps dislike such treatment, not just UcD™ or NCORE® amplifiers.
https://www.hypex.nl/FAQ-Hypex/Cables-and-connections/Can-I-use-a-class-D-amplifier-with-a-Tube-pre-amplifier