• 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.

Interstage coupling cap replace or bypass?

If you look for dirt under the rug, you will find it, even if you have to use a magnifying lens.
Yeah. The problem is given how good we are getting with low distortion and noise, that stuff under the rug is not so well hidden anymore. Add some very good ESL speakers (say, recent generation Sound Lab) and the dirt is all the more plain to see.

Regarding phase noise in dac clocks, here is a plot from one of my clocks in use today:
1709255848758.png