Burn-in time for a Shuguang 845B tube?

In my experience, new 845 tubes take around 50-75hrs to open up. In the early burn in stage, you will find the dynamics restricted. Unlike some other power tubes, 845 tubes should not be left on unattended, therefore, the break in stage will generally take longer. Patience will be rewarded.

Chuckie, some will argue that no tube amplifier should be left unattended to avoid the risk of fire in the event of a catastrophic tube failure. 845, 805 and 211 based amplifiers have over 1000v applied to the tube’s grid, therefore, by the nature of their design, present a greater risk of fire in the event of a catastrophic tube failure.

Leaving an 845, 211 amplifiers on and unattended will not hurt the tubes and will accelerate the burn in process, but as a general rule, it is not a safe practice.

I forgot to mention that tubes have the greatest chance of failure in their first 25 hours of use. Even if you buy tubes used or have them burned in at the factory, tube internals can shift during shipping, and this is more true the larger the tube like an 845, 805 and 211 etc.

PS – don’t forget to check the bias during the tube’s burn in process.

My experience has been that the graphite plate 845 take less time to burn in than metal plate 845.