I bought one when it came out back in the 1970's and a part of me still misses it.
Always loved the sound and the switches and knobs had a strangely sensual feel.
As to leaving it on, sorry I can't help.
Sansui Au9500 - Leave it on?
Picked up a Sansui Au9500 with matching tuner a few days ago. I am dumbfounded at this thing! It's not been totally recapped but has been serviced with quite a few parts replaced and biased etc. Sounds huge detailed and warm. Sounds to me like a nice tube amp with Balls. Build quality is off the charts. What would the consensus be for longevity of the unit? Leave it powered all the time or turn it on and off? What would be less stress on the amp.