Recently, I had another minor issue with my Alpha 9500 amplifier. I had not used the amplifier in a few months, and it would not tune up, faulting with an error code that indicated "low gain." My first impression was the Chinese tube supplied by Alpha/RF Concepts had become defective. Therefore, I switched out the original tube with my spare 8877, this action restored the amplifier to its original working condition.
However, just to ensure the original tube was defective before it was discarded, I reinstalled that tube. The amplifier then began to work fine with the original tube. I can only assume that the tube was not making good contact in the tube socket, and reseating the tube resolved the issue.
Otherwise, I still enjoy using the amplifier from time to time, I believe it is one of the best legal limit amps you can own. Nevertheless, the main amplifier in use at AB4D is a Yaesu Quadra. IMO, using a Yaesu transceiver mated to a Quadra, is still one of the most seamless amplified stations you can run.