I have an original ZTPRE. I think my tubes are dead.  I am not sure what tubes are in this preamp.  Steve what tubes are in here?

After taking the lid off the preamp and the lid off the tube cage the tubes are hot!  And the sound came on.  Don't ask I don't know. I just know that I now have glorious sound!!!!!!

I hate it when I don't know what caused the problem!!