Just to be clear; although I've found I can tell by ear if my A string is in tune, I always check with my tuner as well. I don't trust my ear that much!
In both my orchestras we tune to the oboe. However, when the oboist plays their A, they always have an electronic tuner on their stand to make sure they're right on pitch. lol
IMO every violinist should practice tuning their violins without a tuner. Not necessary tuning in fifths from only the A, but to try to tune each and every string to a played note. It's a excellent aural practice and good for your intonation. If you can hit a right fingered note, you should be able to do the same thing while tuning the violin. It's pretty much the same. A lot of tuning apps have a feature that allows you to play the open notes. This is a great way to start.
'Armed with theory, practice becomes meaningful. Through practice, theory becomes fulfilled.' - Egon von Neindorff.
The strange thing is an oboe's pitch is not fixed at all - when you get tired and your embouchure gets more relaxed, you can end up pretty flat. And if you've already over-compensated at the tuning-up, then it's not funny! It doesn't worry you when you are inexperienced, but then when you become aware of it, it's quite scary. With hindsight, if I could go back, I'd tell myself to think about the difficulties and practise them at home!
Remember.... it is still critical to tune to the orchestra, whether everyone is precisely at A 440 Hz is not quite as important as being in tune together.
Tuning by ear is a very good skill and will serve you well, especially in orchestra. The violin Section Leader will generally give the A that the strings will tune to. So listening and hearing this and tuning to it will be important. The conductor will sometimes ask you to change a specific player's tune as well.
I constantly work on my ear. Not only to tune the strings beginning each practice, but also to hear my intonation while I play. The tuner does not decide what note I play... I do.
It's awesome that you are listening for the correct note! You are training your ear. And that will continue throughout your entire playing life.
- Pete -