AH Njoe Tjoeb CD player, valve Compatibility

[emperor]

have a AH NJoe tjoeb 4000 CD player, and running it are a lovely pair of old, (now even older) at the time new stock, Telefunken EC88/6DJ8,s.

Im cringing and waiting for them to give up the ghost, as it has been 4 years since i bought them.

They have been used many times, and they sound beautiful. So, I searched on the web for some info, on compatible tubes, one guy quoted on a post , "you can try any tube with the AH, as the Tubes only add colour to the sound, and do not have a major functional role. any valves with a 9 pin, will work!.

So, looking for some fun I bought a cheap pair of ECC83/12ax7 JJ /Tesla Amplifier Valves. just as a standby, and tryout pair, until i can afford some better ones.

On power up, there was a mush of muffled fluttering distorted sound, and i switched it off sharply. I have some stock philips tubes, Jan 9772. They and the Telefunkens work perfectly.

Were the tubes incompatible?, are or the tubes a crock of ****, or have i been told the wrong advice?.

Any comments would be greatly appreciated, i am just happy that my Cd player still works, but googling has not been to fruitful, for the 3 hours i have searched for a list of compatible valves

thanks for any answers