From a Collins Radio customer:

Just wanted to mention that sometime ago I purchased a set of tubes from you for the 75A-2. The receiver had no audio or reception to speak of. I decided to replace all of the tubes at once. What a difference! All the ones you sent must have been pretty good because the receiver is hearing like a champ! Keep providing these tube sets. They are filling a void. Thanks for a fine product. I'll be a future customer for other rigs I'm sure.
73, Joe