How to get a 'vintage sound' in your recordings
If you run a few recordings of varying vintages through an audio spectrum analyzer (also known as an audio spectrograph) you will notice that modern recordings tend to have more bass and more top end.
The reason for this is that in the era that we consider vintage - the 1950s and 60s - few people had a listening system that could reproduce much in the way of highs and lows. The photo above shows an example.
Engineers and producers therefore concentrated on what people would actually hear when they bought the record, and of course how the record sounded on radio.
It is worth considering therefore when putting your sounds together that if you monitor on loudspeakers that have the vintage sound, then your attention will be concentrated on the 'vintage frequencies'. (By which I mean the frequencies that were important to listeners in the vintage era.)
Note that I am not only talking about mixing and mastering, I am talking about the whole process of recording from beginning to end.
In fact I would go so far as to say that it doesn't matter how much vintage and retro equipment you have, you are never going to achieve a convincing vintage sound unless you go through the entire recording process this way.
Having said all of that, it is of course well worth bearing in mind that today's listeners very often do have the benefit of playback equipment that is capable of a full frequency range, and your eventual mix and master should please them too.
But if you have put all of your powers of mental concentration into the all-important midrange, you should be able to achieve a mix that would satisfy any lover of vintage sounds.