Well the main weight in an SS poweramp is the power supply (transformer), so it would seem it has lots of gusto (9kg
, do you have enough power to feed it ?) Though a B200s is 7.25 kgs, but the G500s is 10.5kgs (and a tube amp would be even more).
Anyway that aside, how long warm up ??, if it's your preamp then it will be the same for all your amps, as you are saying this is unusual, then it seems something poweramp related ? Now maybe it's something related to building up the appropriate amount of herbivorous in the poweramp
, I think unlikely though but MJMP or others may be able to throw some light on it. One question, how many watts is it and how much power does it need (are you feeding it the amount of malted barley it wants and quickly enough ?, I suspect you are and there shouldn't be an issue but worth noting).
My (unfortunate) suspicion is there is something in the amp that is coming good when it gets warm, or it should be up to full vol very quickly (it doesn't have to warm up tubes...). With SS amps, you press the go button and they work..
Edit: What Harley is saying makes sense, give it a few goes, it may settle down, the good thing is you really like the tone (and that's the most important). You could also re-flow it (hey can't hurt).