I have heard that equipment manufacturers use JJ's because they last longer. I am not sure if its's true but my Luxman had JJ's with the Luxman branding. I will have to say that they do not sound good. I replaced them and it was a huge upgrade. You should try some RCA clear tops (12AU7) (low cost) or some Mullard or Telefunken (12AX7 OR 12AT7) if you don't mind paying more. Some of the new ones are pretty good and cheaper Than NOS.
JJ preamp tubes - repeated problems
I purchased an amplifier that came with stock tubes made by JJ. There were problems with the amplifier so I replaced some tubes and then figured out it was the pre-amplifier tubes and small tubes. The manufacturer in this case who is McIntosh did send me replacement tubes and they worked for a month or so and then began to crackle. Now I have to figure out which of the six small tubes is creating a problem.
I'm curious to know if manufacturers test the tubes that they use in the amplifiers before they ship them out? Maybe they test fine and then go bad within a month. I'm very suspicious they don't bother testing their tubes.
Judging by the process to test individual tubes and when you have 24 tubes on an amplifier I can understand them not giving them much attention during the manufacturing process. Maybe they expect people to replace all the tubes just like the power cords they send out.
.Many replace the stock tubes immediately with gold lions which seems like an easy choice. Maybe manufactures do test their tubes and they're just using a poor manufacturer.
Do others have tube problems with McIntosh amplifiers?