Who and what are BEL/Bell Labs amplifiers

I have noted several times the existence of a company called BEL or BELL Labs and their amps seem to be geared towards the high end market, and yet, I cannot find any sort of information about them, just the fact that they sometimes appear in the used market. What sort of company is or was BEL/BELL and what is the typical sound and look of their units. Are they simply a relic or are they just some very well kept secret. Is there are website with detail description of them?
I just purchased a v3. Anybody know what the vintage of a v3 would be?  It works fine, but I'm wondering about replacing the caps at some point.  Thanks, Peter
I sold a MKII in 2011. As far as possessions go, it was prized. Just hooked a MKV, which I feel lucky to have found. To paraphrase aahmed, I’m going to keep this one.

Interestingly, this one has a silver faceplate. It appears to be stainless steel, and not aluminum... Interesting.
Dick Brown helped me repair my original MKII, over a couple of phone calls, way back when.  He said to pull out the soldering iron and not to be scared.   What a wonderful guy.   
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