got a jcm 800 2204 recently and it sounded good but i sent it for a service since i didnt know when it last had one. when i got it back im finding it seems way louder than it should be and has lots of feedback even at low low volumes.

i know new valves might increase the volume slightly but it doesnt seem right. my amp is a 50w head and by comparison my 100w jcm 900 at volume 3 is same as jcm 800 at volume 1.

could amp have been biased too hot or something?
The tech probably biased it to run hotter.

Stock biasing is usually set on the cold side.
Did they replace the tubes? The old ones could've been worn out and the last time the bias was set, it could've been too low. You may have a microphonic preamp tube causing the feedback. Contact the service center for advice.
Being biased too hot won't make it louder. An amp can't really be 'louder than it should be.' If it's louder, it's because something was wrong before and it wasn't running as efficiently as it could be. If the bias is too hot the tubes will redplate and break up sooner, but a bias change wouldn't account for the volume increase you experienced.

That's assuming that your tech didn't screw with the volume pots or anything, but that would be unusual. It sounds like your old tubes were worn out, and now you're just hearing the amp as it's supposed to be.
Yeah,man. Where is this magical tech, and how much do I have to pay him to make my amps louder?
Sounds to me like you should just use the 100w here if you have a specific purpose in mind and consider this a gift
Grossly incorrect bias settings can reduce an amplifier's output. It's possible it was rectified.
Or not.