[Amps] Warm up and on time question...

[Dave Cole]

Hello,

I have an AL-82, my habit is to turn it on, allow it to warm for about 5
minutes prior to use, use the amp, then turn it back off.  Sometimes I
find that I will be using the amp again within 10 or 15 minutes, maybe
30 minutes.  Is it better to leave it on for the half hour, or turn it
off then re power it 30 minutes later.  

Does this cause any issues over the long term?  Should I just leave it
on for the half hour?  Worried about repeated heating and cooling of the
tubes.

Dave
NK7Z