[bradpdx]

In Standby there is no B+ applied and so no power dissipation beyond the heater filaments. Any tube wear would be minimal at best.

If it helps, consider that back in the day of all-tube recording studios much gear was left in standby forever - filaments were never turned off in order to maintain a consistent temperature and thus reduce noise (no temperature changes to generate noise).

There is even an old-school of thought that believes that tubes are generally happier when the filaments are always on. I won't go into a technical definition of "happy" here, but I think you get the drift.

So, no worries.