The final stage of the preamp is a cathode follower with an active pull-down, which is cap-coupled to the RCA output. The output is shunted by a large-value resistor to discharge the output cap. Don’t remember if there is a muting relay to mute the output during power-up or power-down. In the meantime:
1) ALWAYS power on the DS Preamp before activating your power amp. I’d give it a full minute to glow and stabilize operation before powering on the power amp. If any of the tubes do not light, do not use it. If the tubes make weird scratching or whirring noises, they need replacing.
2) When powering down, turn off the power amp FIRST, then power off the preamp about 10 seconds to a minute later. (You want the power amp fully discharged and providing no gain. No clicks should audible at all.)
I would definitely NOT power on or power off the full system on a common power outlet. If you are using a 12V relay system, you need to add logic to add the delays shown above.
This recommended power-on/power-off sequence applies to all mixed tube/transistor systems (with a few exceptions, noted below). The vast majority of tube preamps use cathode followers with the cathodes (the output node) at 100 to 150 volts DC. The coupling cap blocks the DC, but there can be transients when power goes on or off, as the cap charges or discharges.
The Raven preamp Don and I designed is an exception, because it is transformer coupled, not cap coupled, so on/off transients are far smaller (the transformer does not have a DC charge on it, and the preamp is internally balanced). The DS preamp you have is a superb preamp, but it is a more traditional design with cap coupling in the output section (there are no caps anywhere else, though).
All-transistor or all-tube systems can be switched on a common power switch, but it’s not good practice, since small DC transients can make it through the power amp, get amplified many times, and harm the loudspeaker (and startle the listener). The safest and least annoying approach is following the above sequence.
(Some manufacturers mitigate the problem with muting relays, but it is difficult to find relays that can switch 150 volts without developing contact deposits over time. A low voltage "dry circuit" which does not arc (typical input selecting relays or volume controls) is not a problem, but a high voltage relay that can tolerate a 150 volt arc is extremely difficult to work around. It makes no difference if a 120/240 volt light switch develops a little distortion, but the output of a preamp is one of the most critical nodes of the entire hifi system.)
