I have and own one, as well as a few 7728. They are warmish, and decently detailed tubes, with good balance and punch. The earlier square getter versions of which are impossible to find have the magic mids and deeper bass. They have a unique stage presentation, which is more taller and deeper than wide, and have huge soaring vocals. They are not the last word in transparency/bandwidth and are more on the fun side with a bit of middbass bloom that can punch quite hard, and are a bit rolled off and smooth in the highs.
Bummer I’ll probably stick to the Siemens Halske then.