Preamp replacement

[Shevel]

Hi! I have an old 30w guitar amp with reverb and effect loop. i don't like his sound so much so i want to replace the original preamp by a diy preamp.

I now that i can put my output on power amp imput but if i do that, i will lost the reberb.

I can show you a layout of the original preamp without value. If i plug the input on the blue wire, i have a sound but the reverb won't work.

Please help me.