Can anyone tell me how to get into the preamp section of an altec M 30?
There are no screws on the 175 body, the cable goes in the back and that's it. The tube is in there so i know the guts can come out. My concern is doing damage to the amp just getting the thing apart.

Any suggections?

You can unscrew the entire body from the base of the mic (the piece where the cable comes in). The pipe like body and capsule will come off and you'll be able to get at the tube. The capsule also unscrews so you can replace it with another.
Good luck