My first problems with 12AX7 failing as CF started 10 years ago. The funny thing is they started exactly with EH. Some of them were dying after the first power up. Some of them later. Interestingly pieces from the previous batch were OK. Go figure. So after some digging in the net I learned that the problem was not specific to the EHs only and other brands would also fail as CF. After that I started raising the heaters to 70-80V just to be on the safe side and that cured the problem permanently.On the other hand I read somewhere that the Electro-Harmonix version was especially suitable for this task.
Then I asked myself the question how come Mesa DR is running the CF tube crazy voltages where the cathode to heater difference is more than 200V and I found out that they were using predominantly chinese tubes. I noticed the same thing with other companies as well. So if you need a tube that can withstand the abuse it looks like the chinese 12AX7 can handle it well.
Concerning the protection I'm using the technique described here:
The Valve Wizard