Bad Orchestra in Böhm's 1966 Tristan

A couple of months ago, I bought Karl Böhm's oft-recommended 1966
recording of Tristan and Isolde. However, I couldn't help but notice
that the orchestra screws up badly during the prelude. For example,
the violins are too loud, and there is way too much vibrato. I haven't
read anything about this, but the Penguin Guide hinted at it by saying
that the orchestra "isn't always immaculate."

However, I'm wondering if there was just something wrong with the CD.
The recording I own is the 1992 Philips, not the more commonly owned
1997 DG. Is there a difference?