Reason I ask ... Usual routine is to turn the amp on early afternoon for a listening session, then it'll sit until late evening before I spin another disk. Eight hours is too long probably to just leave it on, but maybe not long enough to turn it off and then back on again? In a perfect world, I could just have the heaters idling away so it's ready to go and doesn't have to go thru an unnecessary hot/cold cycle.
Seems like it'd be simple enough to mod a TDR board to use a manual switch instead of tripping automatically after a time delay ... or better yet ... both? In a perfect world, the TDR would work as intended to soft start the amp automatically, but I could manually switch to standby between sessions, then just turn the amp off at the end of the day.
I also found this ...
http://www.singlecoil.com/docs/standby.pdf
That circuit uses one DPDT to allow either just the AC heater circuits or full power to the amp. I've done similar with ham amps and radios ... some have expressed concern about transients as you flip the switch, but I don't expect it'd be any harder on the amp than a relay, unless you're a really sloooooooow flipper ...