Is it a OK to leave tube pre-amps powede up 24/7

I don't think there's any one right answer to this question.  It depends on how hard the component is on tubes, how long the component takes to "gel" from a cold start, time between listening sessions, how unpalatable (or conversely, inconsequential) re-tubing is to the owner, etc.

For example, my tube preamp (with internal phono stage) sounds great after a couple hours of warm-up. My tubed DAC, on the other hand, doesn't start to sing until it's been on at least 24 hours.  As I'm primarily a weekend listener, I power things up on Friday morning before I go to work, ready for listening Saturday morning, and then turn things off Sunday evening.  The DAC doesn't sound terrible after it's been on for an hour or so, but doesn't get the goosebumps going at that point.  Neither piece is hard on tubes (a long time ago I had an Audible Illusions preamp that ate tubes for breakfast), and if either of these components were tube eaters my approach would change as I'm using some pricey NOS tubes.  Finding out how long the tubes last in your pieces will take....well, will take until you need to buy new ones. :) 

From a safety/power consumption standpoint there's nothing to worry about with a preamp or phono stage if left on 24/7.  If I could listen every day as you do, I'd just leave mine on.

@czarivey

Please detail how it's unsafe with all tube preamps (beyond the ultimate safety practice of just never turning it on at all).

@czarivey 

1. tubes dissipate heat that dries out electrolytic caps.
2. occasionally blown tube can blow other circuit components or even set circuit board on fire.

1. So do transistors
2. I've owned tube equipment for 25 years and have never had a tube "blow."  I've never even seen one on TV.  And should a tube go into thermal or current runaway, there are fuses or sacrificial resistors to shut off the juice, at least in modern and properly designed units (in which category both of the OP's components fall).

Any component can fail, and I'm sure there are cases of spectacular failure.  But that goes for both tube and solid state and is the exception.  Cars can catch on fire too.  Most don't.