Genz Benz: red or black?

[mindismoving]

i just opened up my genz benz el diablo 100 to clear some dust before i change the tubes (came with svetlanas.. i thought it was supposed to have ruby tubes?) and without thinking i disconnected the red and black input/output jacks and now i'm not sure which is which. any help is greatly appreciated!

[MJN]

Looking at the amp from the back, red cable plugs into left side of reverb tank, white on the right.