Can anyone tell me when XLR connections were first used on stereo equipment. (what years)?

Thanks audioquest4life, that was informative. But they didn't name any stereo brands that used balanced XLR cables for their components other than speakers and microphones. I'm interested in the earliest use of XLR connectors for amps, preamps and receivers.

Thanks jwei. I'm going to surmise XLR connections were mostly limited to units that fell in the mid to upper levels of hifi. I'll look into components manufactured in the 90's and after.

Thank you all for your input. XLR has quite an interesting history. Can anyone recommend other stereo brands that used XLR in and out connections? Mid-fi  and no tubes is preferred. Thanks.