I have, in my Wyetech Opal. They work beautifully, a large improvement. Make sure they are genuine though. I bought mine from a gentleman named Paul Lindeman, who has been very reliable.
I have 3 pair of 1578 stamp .
I placed 1 pair in front of Cary SLP-98 and pair of GTB at back.
The result was very musical...too bad I sold my slp-98 and rest of my tube amps.
But now eyeeing for another SLp-98 to match my newly acquired vintage Threshold 4000amp.
Again it will work better than others 6sn7.