Years ago Audio Research had a similar problem with the 6DJ8s in the SP-10 (when you tried to use a low output MC cartridge). The tubes would only last about 2 weeks. Higher output cartridges allowed you to run the tubes *a lot* longer.
If the 6DJ8/6922 is not set up right, there are a number of design parameters that can cause it to go noisy prematurely:
* the tube requires a thorough warmup without B+, so you need a time delay circuit
* its possible to 'starve' the plate, and while you get good gain, the grid will eventually get contaminated, so
* its better to run the tube hot and get less gain.
It was the experience with the SP-10 that made us realize that when we did our preamp that it would probably be a good move to avoid 6DJ8 family tubes. They are not intended for audio, so low noise and low microphonics are challenging (although they are quite linear).
If the 6DJ8/6922 is not set up right, there are a number of design parameters that can cause it to go noisy prematurely:
* the tube requires a thorough warmup without B+, so you need a time delay circuit
* its possible to 'starve' the plate, and while you get good gain, the grid will eventually get contaminated, so
* its better to run the tube hot and get less gain.
It was the experience with the SP-10 that made us realize that when we did our preamp that it would probably be a good move to avoid 6DJ8 family tubes. They are not intended for audio, so low noise and low microphonics are challenging (although they are quite linear).