Should Class A Amps be left on??

continuing this conversation after a time gap of roughly 19 years....

I recently acquired a Sumo nine class A power amp and Sumo Athena preamp. The preamp has a on/off switch that works but the powr amp on/off switch is broken. I currntly have them plugged into two independent surge protectors. I turn them on an hour or two before listening. 

These Sumo amps are 40 years old. I have no idea of their history.

I want to leave them on all the time, but of course they do not have standby mode.
I am afraid to leave them on while unattended.
But also worried about turning them on once every day, the sudden inrush current could damage the powr supply in the amps.

Any advise what to do in this sitatuion? Are there any reaaonably priced slow start/safe start for home audio? I only find lots of different options for surge protectors and power conditioners. Do these surge protectors and power conditioners protect against sudden spike in current while turning the switch on?
Thanks.

Thank you @jjss49 
@jasonbourne52 
@ebm 
@wrm57 
@georgehifi 
@gryphongryph
@jaytor 
@audiojan 

Thanks for the detailed replies.
As advised I will turn it on hour before listening and turn it off for the night.
The preamp I will keep it on 24/7, Sumo Athena preamp, also super old roughly 35-40 years old. Preamp does not have standby. But the user manual says "where possible keep it on all the time".

One day the setup sounds great, but the next day sounds little bit harsh. I am using JBL L5 floor standers.

Thanks @jjss49 
Sure I will do that.
Thanks.