I still haven't bought any tube preamp but I did some tests with a setting inspired by what you all recommanded: Shure 55sh (basically a shure sm57, nothing fancy) into preamp/delay pedal into germanium overdrive into small vox amp (30 years old, the only controls are Tone and Volume, and I'm not even sure about the wattage but I think it's something like 15 watts).
IT SOUNDED GREAT! I used a 50ms delay, the echo having less volume than the dry signal, so you almost can't hear it in normal conditions, but when you turn on the overdrive you start noticing it, it gives a very good rockabilly vibe! It's the first time that I'm using an OD on a mike, but I instantly thought of this one: the Germanium OD by Electro Harmonix, I often use it in guitar because with an other OD before, and the nice setting of course, you can get a Sonics like sound (yes, it sounds like a cranked amp with a pierced speaker, just like the sound of Louie Louie, that made me fall in love with garage instantly). This OD doesn't have a lot of gain, and a very unique texture, very warm (like all effects equipped with germanium transistors), that's why it's perfect for vocals! I'm actually really impressed by this pedal, I usually don't trust big brands when it comes to effects, nothing sounds worse than Boss to my ears for exemple, but Ehx seems to manage to make great sounding pedals with a low cost.
I don't know what this setting will be like without a small amp, because I can't really bring the amp during rehearsals every week, but I'll try it straight into the console, if it doesn't sound well, I'll try to use a tube preamp to see if it helps.
I would recommand to anyone into garage to test the od I talked about, or at least to listen to some demo on youtube, because I've never been that much impressed by a pedal, considering it's price, and I own quite a few boutique pedals!
And no I'm not paid by ehx to do advertising (Though that would be a sweet job for a 18 years old like I am), I'm just very much in love with the sound I got :), I'll try to record something when I have some time so you can judge by yourself the tone you can get this way.