Specification of 5U4C and 5Z4GT

I thought I got 5Z4G tubes from E-bay auction but the seller keep sending 5U4C from Russia. I am not sure that I can use these tubes to replace my pre-amp 5Z4GT tubes. What is difference between 5Z4G and 5Z4GT(original tube on the pre-amp)? Pls advise. Many thanks in advanced.
The difference between a 5Z4G and a 5Z4GT is the shape of the tube, they have the same specs.

My tube manual does not list a 5U4C, only a 5U4G. If it is a 5U4G, then the specs are quite a bit different than the 5Z4G. The 5U4G draws 1.5 times more filament current, drops twice as much voltage, and can supply about twice as much current. If I was stuck on Gilligan's Island and needed this to get my radio working I would use it. The pins are the same so it will plug into the same socket and work provided your amp can supply the extra filament current it will draw. My tube substitution guide does not list it as a match so it doesn't look like a good substitute to me.
thanks Herman