help with tube amps please!

Hi, Im currently looking at certain tube amps to buy. but im still learning and a few things keep cropping up which i dont what they do! firstly some tube amps have Fx loops whats does this do? and secondly and what do you gain by having midi on your amp? Hope these are direct adn clear enough!
Thanks again!
Jk

An FX loop is just a different way of getting the fx into the signal chain. As opposed to plugging your guitar into each effect, you run the fx into a different set of plugs (the fx loop). There are to camps as to whether or not an fx loop is really a good thing.

Midi for a tube amp will allow you to alter certain parameters of the amp such as channel etc. There are many midi pedal boards that you could then use.

FX Loop:
This allows effect pedals to be patched into the amp between the preamp and the power amp, instead of connecting them between the guitar and the preamp input. The FX loop is a good place for time-based effects like reverb, delay, echo, and flanging. Distortion and wha-wah still sound best between the guitar and the amp.

MIDI:
Musical Instrument Digital Interface circuits allow for computer-controlled switching of effects patches, equalizer settings, channel selection, samples, or anything else that has a MIDI control feature. Often used to switch pre-sets on complicated multi-FX units or modelling amplifiers.