Valve question - difference between ECC83 and ECC83A (and can a 12AX7 be swapped in for the latter?)

Grangousier

So this is a question about valves - though not actually related to amps:

I have an SE Electronics Gemini V microphone, which is awesome, and has an ECC83A valve in it. Recently, when I plugged it in, there was a terrible hum on the valve channel (also a lot of noise on the FET channel, which runs parallel, but let's not worry about that for the moment). I've sent a message to their support desk, but while I'm waiting for a reply, I have the following questions, which will expose my ignorance as much as anything else:

1. Am I right in thinking that an ECC83 and a 12AX7 valve are exactly the same thing just with European and US numbers respectively?

2. Is the ECC83A different enough from the ECC83 that one couldn't be swapped for the other? More to the point if I did take out the ECC83A and replace it with a 12AX7 (because I have a spare one of those sitting here), is it possible to damage the microphone? 

I realise that I can get a Bugera ECC83A valve from Amazon at a very reasonable price, and may do that anyway, but wondered whether it was safe to do 12AX7 experiments today. 

jpfamps

They are all pretty much the same valve and and can be used interchangeably.