This months tube is a wide band output pentode. The industrial tube type 8233 with the european designation E55L.
Looks very good to me! The first two grid lines are a bit closer to each other which indicates that it is better to stay clear of the 0V grid voltage. I anyways always insist on a large headroom and try to avoid that the grid gets more negative than -1V even when driven at full signal. The grid lines in the screen shot are spaced apart in 1V steps. I also noticed a good sample to sample consistency. It is fairly easy to find closely matching tubes. And this is matching plate curves not just matching at a single operating point.
The photo above shows a currently produced socket from China on the left and an old production one on the right.
As mentioned above, this tube was made by various manufacturers. The Philips E55L shown on the right has the exact same internal structure as the Amperex tubes shown above. So they were probably made in the same factory. This tube prominently displays a SQ logo on the other side which stands for special quality. The datasheet states a life time of 10.000 hrs for these tubes. Definitely a tube just waiting to be used for audio applications. I'm looking forward to give this very special tube a try. Most likely I'll first use it in a LCR phonostage. I will report about this in future posts. Stay tuned!